Autologous Schwann cells drive regeneration through a 6-cm autogenous venous nerve conduit

The effects of Garcinia kola and curcumin on the dorsal root ganglion of the diabetic rat after peripheral nerve transection injury

OBJECTIVE

To test the protective effects of Garcinia kola and curcumin on the ganglion tissues of diabetic rats following the use of autologous vein graft in peripheral nerve transection injury.

METHODS

The sciatic nerve on the right side was transected, and anastomosis was performed between the proximal and distal ends using an autologous vein graft. Curcumin and Garcinia kola seed extract were administered daily by oral gavage. The ganglion tissues were harvested after a 90-day waiting period. Sensory neurons in the dorsal root ganglion at the L4 and L5 levels were used for stereological evaluations. Mean sensory neuron numbers were analyzed using a stereological technique. The size of the light and dark neurons was also estimated, and ultrastructural and immunohistochemical evaluations were performed.

RESULTS

A statistically significant difference in sensory neuron numbers was observed between the groups with and without Garcinia kola and curcumin applications. The immunohistochemical results showed that the s-100 protein is expressed selectively between cell types.

CONCLUSION

The results of this study show that curcumin and Garicinia kola prevented sensory neuron loss in diabetic rats following transection injury to the sciatic nerve.

Regenerative Strategies in Treatment of Peripheral Nerve Injuries in Different Animal Models

BACKGROUND

Peripheral nerve damage mainly resulted from traumatic or infectious causes; the main signs of a damaged nerve are the loss of sensory and/or motor functions. The injured nerve has limited regenerative capacity and is recovered by the body itself, the recovery process depends on the severity of damage to the nerve, nowadays the use of stem cells is one of the new and advanced methods for treatment of these problems.

METHOD

Following our review, data are collected from different databases "Google scholar, Springer, Elsevier, Egyptian Knowledge Bank, and PubMed" using different keywords such as Peripheral nerve damage, Radial Nerve, Sciatic Nerve, Animals, Nerve regeneration, and Stem cell to investigate the different methods taken in consideration for regeneration of PNI.

RESULT

This review contains tables illustrating all forms and types of regenerative medicine used in treatment of peripheral nerve injuries (PNI) including different types of stem cells " adipose-derived stem cells, bone marrow stem cells, Human umbilical cord stem cells, embryonic stem cells" and their effect on re-constitution and functional recovery of the damaged nerve which evaluated by physical, histological, Immuno-histochemical, biochemical evaluation, and the review illuminated the best regenerative strategies help in rapid peripheral nerve regeneration in different animal models included horse, dog, cat, sheep, monkey, pig, mice and rat.

CONCLUSION

Old surgical attempts such as neurorrhaphy, autogenic nerve transplantation, and Schwann cell implantation have a limited power of recovery in cases of large nerve defects. Stem cell therapy including mesenchymal stromal cells has a high potential differentiation capacity to renew and form a new nerve and also restore its function.

Peripheral nerve defects repaired with autogenous vein grafts filled with platelet-rich plasma and active nerve microtissues and evaluated by novel multimodal ultrasound techniques

BACKGROUND

Developing biocompatible nerve conduits that accelerate peripheral nerve regeneration, lengthening and functional recovery remains a challenge. The combined application of nerve microtissues and platelet-rich plasma (PRP) provides abundant Schwann cells (SCs) and various natural growth factors and can compensate for the deficiency of SCs in the nerve bridge, as well as the limitations of applying a single type of growth factor. Multimodal ultrasound evaluation can provide additional information on the stiffness and microvascular flow perfusion of the tissue. This study was designed to investigate the effectiveness of a novel tissue-engineered nerve graft composed of an autogenous vein, nerve microtissues and PRP in reconstructing a 12-mm tibial nerve defect and to explore the value of multimodal ultrasound techniques in evaluating the prognosis of nerve repair.

METHODS

In vitro, nerve microtissue activity was first investigated, and the effects on SC proliferation, migration, factor secretion, and axonal regeneration of dorsal root ganglia (DRG) were evaluated by coculture with nerve microtissues and PRP. In vivo, seventy-five rabbits were equally and randomly divided into Hollow, PRP, Micro-T (Microtissues), Micro-T + PRP and Autograft groups. By analysing the neurological function, electrophysiological recovery, and the comparative results of multimodal ultrasound and histological evaluation, we investigated the effect of these new nerve grafts in repairing tibial nerve defects.

RESULTS

Our results showed that the combined application of nerve microtissues and PRP could significantly promote the proliferation, secretion and migration of SCs and the regeneration of axons in the early stage. The Micro-T + PRP group and Autograft groups exhibited the best nerve repair 12 weeks postoperatively. In addition, the changes in target tissue stiffness and microvascular perfusion on multimodal ultrasound (shear wave elastography; contrast-enhanced ultrasonography; Angio PlaneWave UltrasenSitive, AngioPLUS) were significantly correlated with the histological results, such as collagen area percentage and VEGF expression, respectively.

CONCLUSION

Our novel tissue-engineered nerve graft shows excellent efficacy in repairing 12-mm defects of the tibial nerve in rabbits. Moreover, multimodal ultrasound may provide a clinical reference for prognosis by quantitatively evaluating the stiffness and microvescular flow of nerve grafts and targeted muscles.

The Effect of Schwann Cells/Schwann Cell-Like Cells on Cell Therapy for Peripheral Neuropathy

Peripheral neuropathy is a common neurological issue that leads to sensory and motor disorders. Over time, the treatment for peripheral neuropathy has primarily focused on medications for specific symptoms and surgical techniques. Despite the different advantages of these treatments, functional recovery remains less than ideal. Schwann cells, as the primary glial cells in the peripheral nervous system, play crucial roles in physiological and pathological conditions by maintaining nerve structure and functions and secreting various signaling molecules and neurotrophic factors to support both axonal growth and myelination. In addition, stem cells, including mesenchymal stromal cells, skin precursor cells and neural stem cells, have the potential to differentiate into Schwann-like cells to perform similar functions as Schwann cells. Therefore, accumulating evidence indicates that Schwann cell transplantation plays a crucial role in the resolution of peripheral neuropathy. In this review, we summarize the literature regarding the use of Schwann cell/Schwann cell-like cell transplantation for different peripheral neuropathies and the potential role of promoting nerve repair and functional recovery. Finally, we discuss the limitations and challenges of Schwann cell/Schwann cell-like cell transplantation in future clinical applications. Together, these studies provide insights into the effect of Schwann cells/Schwann cell-like cells on cell therapy and uncover prospective therapeutic strategies for peripheral neuropathy.

A Rabbit Model for Peripheral Nerve Reconstruction Studies Avoiding Automutilation Behavior

Background  The rabbit sciatic nerve injury model may represent a valuable alternative for critical gap distance seen in humans but often leads to automutilation. In this study, we modified the complete sciatic nerve injury model for avoiding autophagy.

Materials and Methods  In 20 adult female New Zealand White rabbits, instead of transecting the complete sciatic nerve, we unilaterally transected the tibial portion and preserved the peroneal portion. Thereby loss of sensation in the dorsal aspect of the paw was avoided. The tibial portion was repaired in a reversed autograft approach in a length of 2.6 cm. In an alternative repair approach, a gap of 2.6 cm in length was repaired with a chitosan-based nerve guide.

Results  During the 6-month follow-up period, there were no incidents of autotomy. Nerve regeneration of the tibial portion of the sciatic nerve was evaluated histologically and morphometrically. A clear difference between the distal segments of the healthy contralateral and the repaired tibial portion of the sciatic nerve was detectable, validating the model.

Conclusion  By transecting the isolated tibial portion of the rabbit sciatic nerve and leaving the peroneal portion intact, it was possible to eliminate automutilation behavior.

Spider silk nerve graft promotes axonal regeneration on long distance nerve defect in a sheep model

Peripheral nerve injuries with substantial tissue loss require autologous nerve transplantation or alternatively reconstruction with nerve conduits. Axonal elongation after nerve transection is about 1 mm/day. The precise time course of axonal regeneration on an ultrastructural level in nerve gap repair using either autologous or artificial implants has not been described. As peripheral nerve regeneration is a highly time critical process due to deterioration of the neuromuscular junction, this in vivo examination in a large animal model was performed in order to investigate axonal elongation rates and spider silk material degradation in a narrowly delimited time series (20, 30, 40, 50, 90, 120, 150 and 180 days) by using a novel spider silk based artificial nerve graft as a critical prerequisite for clinical translation. Autologous nerves or artificial nerve conduits based on spider silk of the spider species Trichonephila edulis were transplanted in a 6.0 cm nerve defect model in the black headed mutton. At each of the post-implant time point, electrophysiology recordings were performed to assess functional reinnervation of axonal fibers into the implants. Samples were analyzed by histology and immunofluorescence in order to verify the timeline of axonal regeneration including axonal regeneration rates of the spider silk implant and the autologous transplant groups. Spider silk was degraded within 3 month by a light immune response mainly mediated by Langhans Giant cells. In conjunction with behavioral analysis and electrophysiological measurements, the results indicate that the spider silk nerve implant supported an axonal regeneration comparable to an autologous nerve graft which is the current gold standard in nerve repair surgery. These findings indicate that a biomaterial based spider silk nerve conduit is as effective as autologous nerve implants and may be an important approach for long nerve defects.

Adipose tissue stem cells in peripheral nerve regeneration-In vitro and in vivo

After peripheral nerve injury, Schwann cells (SCs) are crucially involved in several steps of the subsequent regenerative processes, such as the Wallerian degeneration. They promote lysis and phagocytosis of myelin, secrete numbers of neurotrophic factors and cytokines, and recruit macrophages for a biological debridement. However, nerve injuries with a defect size of >1 cm do not show proper tissue regeneration and require a surgical nerve gap reconstruction. To find a sufficient alternative to the current gold standard-the autologous nerve transplant-several cell-based therapies have been developed and were experimentally investigated. One approach aims on the use of adipose tissue stem cells (ASCs). These are multipotent mesenchymal stromal cells that can differentiate into multiple phenotypes along the mesodermal lineage, such as osteoblasts, chondrocytes, and myocytes. Furthermore, ASCs also possess neurotrophic features, that is, they secrete neurotrophic factors like the nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, ciliary neurotrophic factor, glial cell-derived neurotrophic factor, and artemin. They can also differentiate into the so-called Schwann cell-like cells (SCLCs). These cells share features with naturally occurring SCs, as they also promote nerve regeneration in the periphery. This review gives a comprehensive overview of the use of ASCs in peripheral nerve regeneration and peripheral nerve tissue engineering both in vitro and in vivo. While the sustainability of differentiation of ASCs to SCLCs in vivo is still questionable, ASCs used with different nerve conduits, such as hydrogels or silk fibers, have been shown to promote nerve regeneration.

Functionalized nerve conduits for peripheral nerve regeneration: A literature review

Functionalized neurotube are a third-generation of conduits with chemical or architectural bioactivity developed for axonal proliferation. The goal of this review is to provide a synopsis of the functionalized nerve conduits described in the literature according to their chemical and architectural properties and answer two questions: what are their mechanisms of action? Has their efficacy been proven compared to the autologous nerve graft? Our literature review relates all kind of conduits corresponding to functionalized neurotubes in peripheral nerve regeneration found in Medline and PubMed Central. Studies developing nerve gaps, chemotactic or structural features promoting each conduit, results, efficiency were selected. Fifty-five studies were selected and classified in: (a) intraluminal neurotrophic factors; (b) cell-based therapy (combined-in-vein muscles, amniotic membrane, Schwann cells, stem cells); (c) extracellular matrix proteins; (d) tissue engineering; (e) bioimplants. Functionalized neurotubes showed significantly better functional results than after end-to-end nerve suture. No studies can be able to show that neurotube results were better than autologous nerve graft results. We included all studies regardless of effectives to evaluate quality of reinnervation with modern tubulization. Functionalized neurotubes promote basic conduits for peripheral nerve regeneration. Thanks to bioengineering and microsurgery improvement, further neurotubes could promote best level of regeneration and functional recovery to successfully bridge a critical nerve gap.

An update on the management of nerve gaps

No abstract required

Application of stem cells in peripheral nerve regeneration

Traumatic peripheral nerve injury is a worldwide clinical issue with high morbidity. The severity of peripheral nerve injury can be classified as neurapraxia, axonotmesis or neurotmesis, according to Seddon's classification, or five different degrees according to Sunderland's classification. Patients with neurotmesis suffer from a complete transection of peripheral nerve stumps and are often in need of surgical repair of nerve defects. The applications of autologous nerve grafts as the golden standard for peripheral nerve transplantation meet some difficulties, including donor nerve sacrifice and nerve mismatch. Attempts have been made to construct tissue-engineered nerve grafts as supplements or even substitutes for autologous nerve grafts to bridge peripheral nerve defects. The incorporation of stem cells as seed cells into the biomaterial-based scaffolds increases the effectiveness of tissue-engineered nerve grafts and largely boosts the regenerative process. Numerous stem cells, including embryonic stem cells, neural stem cells, bone marrow mesenchymal stem cells, adipose stem cells, skin-derived precursor stem cells and induced pluripotent stem cells, have been used in neural tissue engineering. In the current review, recent trials of stem cell-based tissue-engineered nerve grafts have been summarized; potential concerns and perspectives of stem cell therapeutics have also been contemplated.

Therapeutic strategies for peripheral nerve injury: decellularized nerve conduits and Schwann cell transplantation

In recent years, the use of Schwann cell transplantation to repair peripheral nerve injury has attracted much attention. Animal-based studies show that the transplantation of Schwann cells in combination with nerve scaffolds promotes the repair of injured peripheral nerves. Autologous Schwann cell transplantation in humans has been reported recently. This article reviews current methods for removing the extracellular matrix and analyzes its composition and function. The development and secretory products of Schwann cells are also reviewed. The methods for the repair of peripheral nerve injuries that use myelin and Schwann cell transplantation are assessed. This survey of the literature data shows that using a decellularized nerve conduit combined with Schwann cells represents an effective strategy for the treatment of peripheral nerve injury. This analysis provides a comprehensive basis on which to make clinical decisions for the repair of peripheral nerve injury.

Nerve grafting for peripheral nerve injuries with extended defect sizes

Artificial and non-artificial nerve grafts are the gold standard in peripheral nerve reconstruction in cases with extensive loss of nerve tissue, particularly where a direct end-to-end suture or an autologous nerve graft is inauspicious. Different materials are marketed and approved by the US Food and Drug Administration (FDA) for peripheral nerve graft reconstruction. The most frequently used materials are collagen and poly(DL-lactide-ε-caprolactone). Only one human nerve allograft is listed for peripheral nerve reconstruction by the FDA. All marketed nerve grafts are able to demonstrate sufficient nerve regeneration over small distances not exceeding 3.0 cm. A key question in the field is whether nerve reconstruction on large defect lengths extending 4.0 cm or more is possible. This review gives a summary of current clinical and experimental approaches in peripheral nerve surgery using artificial and non-artificial nerve grafts in short and long distance nerve defects. Strategies to extend nerve graft lengths for long nerve defects, such as enhancing axonal regeneration, include the additional application of Schwann cells, mesenchymal stem cells or supporting co-factors like growth factors on defect sizes between 4.0 and 8.0 cm.

Application of epineural sheath conduit for restoration of 6-cm long nerve defects in a sheep median nerve model

BACKGROUND

Due to limited number of studies, we tested feasibility of autologous epineural sheath conduit (ESC) in repair of 6-cm median nerve gaps in a sheep-the large animal model.

MATERIALS AND METHODS

Eight ewes, 6-8 months old, 30-35 kg, were divided into three experimental groups: group 1-no defect repair (n = 4 nerves/group), group 2-autograft controls (n = 6 nerves/group), group 3-autologous ESC filled with saline (n = 6 nerves/group). ESC was constructed from a 6-cm long segment of sheep median nerve and tested for expression of laminin B, Glial fibrillary acidic protein (GFAP), S-100 and CD31 using immunofluorescent staining. At 6 months after nerve repair, nerve conduction velocity and somatosensory evoked potentials (SSEP) assessed neurosensory recovery, while histomorphometry tested nerve regeneration.

RESULTS

Ex vivo characterization of ESC, before in vivo nerve gap repair, showed high laminin B expression, which supports axonal growth. At 6 months post-repair, structural integrity of ESC was preserved. ESC was well-vascularized and tissue adhesions were comparable to autograft controls. The maximal conduction velocities (29.80 ± 5.85 ms vs. 32.28 ± 6.75 ms; p = .44), action potential amplitudes (32.68 ± 17.44 mV vs. 44.14 ± 23.10 mV; p = .38) and SSEP amplitude values (6.18 ± 5.84 mV vs. 4.68 ± 2.53 mV; p = .28) were comparable between autograft and ESC groups. Presence of regenerating axons was confirmed in the distal segment of ESC at 6 months after repair.

CONCLUSION

The feasibility of ESC in restoration of 6-cm long nerve defects in a sheep median nerve model was confirmed by nerve conduction assessments and correlated with axonal regeneration tested by histomorphometry. We confirmed ESC potential in support of regeneration of long nerve defects.

Alteration of Sciatic Nerve Histology and Electrical Function After Compression and After Neurolysis in a Diabetic Rat Model

BACKGROUND

Diabetic rats are more sensitive to nerve entrapment. This study was conducted to evaluate nerve function and histological changes in diabetic rats after nerve compression and subsequent decompression.

METHODS

A total of 35 Wistar rats were included. The experimental group was divided into diabetic sciatic nerve compression group (DSNC, n = 5) and diabetic sciatic nerve decompression group (DSND, n = 20). The DSNC model was created by wrapping a silicone tube circumferentially around the nerve for 4 weeks, and then the DSND group accepted nerve decompression and was followed up to 12 weeks. The DSND group was equally divided into DSND 3 weeks (DSND3), 6 weeks (DSND6), 9 weeks (DSND9), and 12 weeks (DSND12) groups. Five rats were taken as normoglycemic control group (CR, n = 5), and another 5 rats as diabetic control group (DM, n = 5). The mechanical hyperalgesia of rats was detected by Semmes-Weinstein nylon monofilaments (SWMs) and by motor nerve conduction velocity (MNCV). These 2 physiological indicators and histology of sciatic nerves were compared among different groups.

RESULTS

The SWM measurements improved toward normal values after decompression. The SWM value was significantly lower (more normal) in the DSNC groups than in the DSND group (P < 0.05). The MNCV was 53.7 ± 0.8 m/s in the CR group, whereas it was 28.4 ± 1.0 m/s in the DSNC group (P < 0.001). Six weeks after decompression, the MNCV was significantly faster than that in the DSNC group (P < 0.001). Histological examination demonstrated chronic nerve compression, which responded toward normal after decompression, but with degree of myelination never recovering to normal.

CONCLUSIONS

Chronic compression of the diabetic sciatic nerve has measureable negative effects on sciatic nerve motor nerve function, associated with a decline of touch/pressure threshold and degeneration of myelin sheath and axon. Nerve decompression surgery can reverse these effects and partially restore nerve function.

Bioactive Silk-Based Nerve Guidance Conduits for Augmenting Peripheral Nerve Repair

Repair of peripheral nerve injuries depends upon complex biology stemming from the manifold and challenging injury-healing processes of the peripheral nervous system. While surgical treatment options are available, they tend to be characterized by poor clinical outcomes for the injured patients. This is particularly apparent in the clinical management of a nerve gap whereby nerve autograft remains the best clinical option despite numerous limitations; in addition, effective repair becomes progressively more difficult with larger gaps. Nerve conduit strategies based on tissue engineering approaches and the use of silk as scaffolding material have attracted much attention in recent years to overcome these limitations and meet the clinical demand of large gap nerve repair. This review examines the scientific advances made with silk-based conduits for peripheral nerve repair. The focus is on enhancing bioactivity of the conduits in terms of physical guidance cues, inner wall and lumen modification, and imbuing novel conductive functionalities.

Adult Stem Cell-Based Strategies for Peripheral Nerve Regeneration

Peripheral nerve injuries (PNI) occur as the result of sudden trauma and can lead to life-long disability, reduced quality of life, and heavy economic and social burdens. Although the peripheral nervous system (PNS) has the intrinsic capacity to regenerate and regrow axons to a certain extent, current treatments frequently show incomplete recovery with poor functional outcomes, particularly for large PNI. Many surgical procedures are available to halt the propagation of nerve damage, and the choice of a procedure depends on the extent of the injury. In particular, recovery from large PNI gaps is difficult to achieve without any therapeutic intervention or some form of tissue/cell-based therapy. Autologous nerve grafting, considered the "gold standard" is often implemented for treatment of gap formation type PNI. Although these surgical procedures provide many benefits, there are still considerable limitations associated with such procedures as donor site morbidity, neuroma formation, fascicle mismatch, and scarring. To overcome such restrictions, researchers have explored various avenues to improve post-surgical outcomes. The most commonly studied methods include: cell transplantation, growth factor delivery to stimulate regenerating axons and implanting nerve guidance conduits containing replacement cells at the site of injury. Replacement cells which offer maximum benefits for the treatment of PNI, are Schwann cells (SCs), which are the peripheral glial cells and in part responsible for clearing out debris from the site of injury. Additionally, they release growth factors to stimulate myelination and axonal regeneration. Both primary SCs and genetically modified SCs enhance nerve regeneration in animal models; however, there is no good source for extracting SCs and the only method to obtain SCs is by sacrificing a healthy nerve. To overcome such challenges, various cell types have been investigated and reported to enhance nerve regeneration.In this review, we have focused on cell-based strategies aimed to enhance peripheral nerve regeneration, in particular the use of mesenchymal stem cells (MSCs). Mesenchymal stem cells are preferred due to benefits such as autologous transplantation, routine isolation procedures, and paracrine and immunomodulatory properties. Mesenchymal stem cells have been transplanted at the site of injury either directly in their native form (undifferentiated) or in a SC-like form (transdifferentiated) and have been shown to significantly enhance nerve regeneration. In addition to transdifferentiated MSCs, some studies have also transplanted ex-vivo genetically modified MSCs that hypersecrete growth factors to improve neuroregeneration.

Fascicular shifting: a novel technique to overcome large nerve defects

OBJECTIVE Over the last decade, a number of authors have investigated the utility of different biological and synthetic matrices as alternatives to conventional nerve grafts. However, the autologous nerve graft remains the gold standard, even though it often involves using a pure sensory nerve to reconstruct a mixed or even a pure motor nerve. Furthermore, limited donor sites often necessitate a significant mismatch of needed nerve tissue, especially for large proximal nerve defects such as brachial plexus lesions. Here, the authors present a new technique that overcomes these problems: the fascicular shift procedure (FSP). A fascicular group of the nerve distal to the injury is harvested in a sufficient length to bridge the nerve defect. METHODS The method of fascicular shifting was tested at the sciatic nerve in 45 Lewis rats. In the experimental group, a 15-mm nerve defect was created and reconstructed with a fascicular group that was harvested directly distal to the gap. This group was compared with 1 negative control group (defect without reconstruction) and 3 positive control groups (sensory, motor, and mixed graft). After 12 weeks of nerve regeneration, outcome was evaluated using retrograde labeling, histomorphometric analysis, and muscle force analysis. RESULTS All reconstructed groups showed successful regeneration with various levels of function. The negative control group showed minimal force measurements that were of no functional value. The fascicular shift provided sufficient guidance to overcome nerve defects, had higher (p < 0.1) motor neuron counts (1958.75 ± 657.21) than the sensory graft (1263.50 ± 538.90), and was equal to motor grafts (1490.43 ± 794.80) and mixed grafts (1720.00 ± 866.421). This tendency of improved motor regeneration was confirmed in all analyses. The mixed graft group was compared with the experimental group to investigate the influence of the potential damage induced by the fascicular shift distal to the repair site. However, none of the analyses revealed an impairment of nerve regeneration for both the tibial and common peroneal index muscles. CONCLUSIONS This study demonstrates that harvesting a transplant from the nerve segment distal to the injury site offers a mixed graft without causing additional donor-site morbidity. These grafts perform statistically better than a standard sensory graft in terms of motor recovery. The fascicular shift presents a novel method to reconstruct large proximal nerve defects, making it immensely attractive in brachial plexus reconstruction.

Cauda equina repair in the rat: Part 3. Axonal regeneration across Schwann cell-Seeded collagen foam

INTRODUCTION

Treatments for patients with cauda equina injury are limited.

METHODS

In this study, we first used retrograde labeling to determine the relative contributions of cauda equina motor neurons to intrinsic and extrinsic rat tail muscles. Next, we transected cauda equina ventral roots and proceeded to bridge the proximal and distal stumps with either a type I collagen scaffold coated in laminin (CL) or a collagen-laminin scaffold that was also seeded with Schwann cells (CLSC). Regeneration was assessed by way of serial retrograde labeling.

RESULTS

After accounting for the axonal contributions to intrinsic vs. extrinsic tail muscles, we noted a higher degree of double labeling in the CLSC group (58.0 ± 39.6%) as compared with the CL group (27.8 ± 16.0%; P = 0.02), but not the control group (33.5 ± 18.2%; P = 0.10).

DISCUSSION

Our findings demonstrate the feasibility of using CLSCs in cauda equina injury repair. Muscle Nerve 57: E78-E84, 2018.

First human experience with autologous Schwann cells to supplement sciatic nerve repair: report of 2 cases with long-term follow-up

OBJECTIVE Long-segment injuries to large peripheral nerves present a challenge to surgeons because insufficient donor tissue limits repair. Multiple supplemental approaches have been investigated, including the use of Schwann cells (SCs). The authors present the first 2 cases using autologous SCs to supplement a peripheral nerve graft repair in humans with long-term follow-up data. METHODS Two patients were enrolled in an FDA-approved trial to assess the safety of using expanded populations of autologous SCs to supplement the repair of long-segment injuries to the sciatic nerve. The mechanism of injury included a boat propeller and a gunshot wound. The SCs were obtained from both the sural nerve and damaged sciatic nerve stump. The SCs were expanded and purified in culture by using heregulin β1 and forskolin. Repair was performed with sural nerve grafts, SCs in suspension, and a Duragen graft to house the construct. Follow-up was 36 and 12 months for the patients in Cases 1 and 2, respectively. RESULTS The patient in Case 1 had a boat propeller injury with complete transection of both sciatic divisions at midthigh. The graft length was approximately 7.5 cm. In the postoperative period the patient regained motor function (Medical Research Council [MRC] Grade 5/5) in the tibial distribution, with partial function in peroneal distribution (MRC Grade 2/5 on dorsiflexion). Partial return of sensory function was also achieved, and neuropathic pain was completely resolved. The patient in Case 2 sustained a gunshot wound to the leg, with partial disruption of the tibial division of the sciatic nerve at the midthigh. The graft length was 5 cm. Postoperatively the patient regained complete motor function of the tibial nerve, with partial return of sensation. Long-term follow-up with both MRI and ultrasound demonstrated nerve graft continuity and the absence of tumor formation at the repair site. CONCLUSIONS Presented here are the first 2 cases in which autologous SCs were used to supplement human peripheral nerve repair in long-segment injury. Both patients had significant improvement in both motor and sensory function with correlative imaging. This study demonstrates preliminary safety and efficacy of SC transplantation for peripheral nerve repair.

The Glia Response after Peripheral Nerve Injury: A Comparison between Schwann Cells and Olfactory Ensheathing Cells and Their Uses for Neural Regenerative Therapies

The peripheral nervous system (PNS) exhibits a much larger capacity for regeneration than the central nervous system (CNS). One reason for this difference is the difference in glial cell types between the two systems. PNS glia respond rapidly to nerve injury by clearing debris from the injury site, supplying essential growth factors and providing structural support; all of which enhances neuronal regeneration. Thus, transplantation of glial cells from the PNS is a very promising therapy for injuries to both the PNS and the CNS. There are two key types of PNS glia: olfactory ensheathing cells (OECs), which populate the olfactory nerve, and Schwann cells (SCs), which are present in the rest of the PNS. These two glial types share many similar morphological and functional characteristics but also exhibit key differences. The olfactory nerve is constantly turning over throughout life, which means OECs are continuously stimulating neural regeneration, whilst SCs only promote regeneration after direct injury to the PNS. This review presents a comparison between these two PNS systems in respect to normal physiology, developmental anatomy, glial functions and their responses to injury. A thorough understanding of the mechanisms and differences between the two systems is crucial for the development of future therapies using transplantation of peripheral glia to treat neural injuries and/or disease.

Advances and Future Applications of Augmented Peripheral Nerve Regeneration

Peripheral nerve injuries remain a significant source of long lasting morbidity, disability, and economic costs. Much research continues to be performed in areas related to improving the surgical outcomes of peripheral nerve repair. In this review, the physiology of peripheral nerve regeneration and the multitude of efforts to improve surgical outcomes are discussed. Improvements in tissue engineering that have allowed for the use of synthetic conduits seeded with neurotrophic factors are highlighted. Selected pre-clinical and available clinical data using cell based methods such as Schwann cell, undifferentiated, and differentiated stem cell transplantation to guide and enhance peripheral nerve regeneration are presented. The limitations that still exist in the utility of neurotrophic factors and cell-based therapies are outlined. Strategies that are most promising for translation into the clinical arena are suggested.

Nerve regeneration techniques respecting the special characteristics of the inferior alveolar nerve

PURPOSE

The aim of this study was to examine the in situ regeneration of the inferior alveolar nerve (IAN) in its bony channel, using autologous tissue in combination with a recombinant human nerve growth factor (rhNGF).

MATERIALS AND METHODS

A total of 20 New Zealand rabbits were randomly divided into five groups. Following dissection of the IAN, the animals underwent reconstruction either with muscle tissue (groups 1 and 2) or with fat tissue (groups 3 and 4). In group 5 (control), the dissected nerve was resected and reconstructed by placement of the reversed autologous segment. After 2 and 4 weeks, 1 mL rhNGF was locally injected in groups 1 and 3. Nerve function was monitored by measuring the jaw-opening reflex using electromyography for a period of 24 weeks.

RESULTS

Regeneration of the nerve was achieved in all groups, but preoperative threshold values were not achieved. Comparing the experimental groups to the control, there was a significant difference in favor of the autologous nerve reconstruction. Differences between the experimental groups remained statistically not significant.

CONCLUSION

Regeneration of the IAN with autologous tissue is possible, but without achieving preoperative thresholds. Additional injection of a growth factor seems to improve the speed of regeneration for fat and muscle grafts.

A Novel Use of Genipin-Fixed Gelatin as Extracellular Matrix for Peripheral Nerve Regeneration

Application of combining herbal medicine and biomedical material science to nerve regeneration is a new approach. In this study, we describe a novel use of purified genipin, which can be extracted from Gardenia jasminoides Ellis, fixing the gelatin to be an extracellular matrix for peripheral nerve regeneration. A 10-mm gap of rat sciatic nerve was created between the proximal and distal nerve stumps, which were sutured into silicone rubber tubes filled with either the genipin-fixed gelatin or collagen gel. Silicone rubber tubes filled with saline were used as controls. Six weeks after implantation, regeneration across the nerve gaps occurred in 80 and 90% of the animals from the groups of genipin-fixed gelatin and collagen, respectively, whereas only 30% in the control group. Large numbers of myelinated axons were also seen in the genipin-fixed gelatin (5104±3278) and the collagen groups (8063±1807). These findings indicated that the genipin-fixed gelatin could be an acceptable extracellular matrix for nerve regeneration.

The Use of Autologous Schwann Cells to Supplement Sciatic Nerve Repair With a Large Gap: First in Human Experience

Insufficient donor nerve graft material in peripheral nerve surgery remains an obstacle for successful long-distance regeneration. Schwann cells (SCs) can be isolated from adult mammalian peripheral nerve biopsies and can be grown in culture and retain their capacity to enhance peripheral nerve regeneration within tubular repair strategies in multiple animal models. Human Schwann cells (hSCs) can be isolated, expanded in number, and retain their ability to promote regeneration and myelinate axons, but have never been tested in a clinical case of peripheral nerve injury. A sural nerve biopsy and peripheral nerve tissue from the traumatized sciatic nerve stumps was obtained after Food and Drug Administration (FDA) and Institutional Review Board (IRB) approval as well as patient consent. The SCs were isolated after enzymatic digestion of the nerve and expanded with the use of heregulin β1 (0.1 µg/ml) and forskolin (15 mM). After two passages the Schwann cell isolates were combined with sural nerve grafts to repair a large sciatic nerve defect (7.5 cm) after a traumatic nerve injury. The sural nerve and the traumatized sciatic nerve ends both served as an excellent source of purified (90% and 97%, respectively) hSCs. Using ultrasound and magnetic resonance imaging (MRI) we were able to determine continuity of the nerve graft repair and the absence of tumor formation. The patient had evidence of proximal sensory recovery and definitive motor recovery distal to the repair in the distribution of the tibial and common peroneal nerve. The patient did experience an improvement in her pain scores over time. The goals of this approach were to determine the safety and clinical feasibility of implementing a new cellular repair strategy. In summary, this approach represents a novel strategy in the treatment of peripheral nerve injury and represents the first reported use of autologous cultured SCs after human peripheral nerve injury.

Peripheral nerve regeneration with conduits: use of vein tubes

Treatment of peripheral nerve injuries remains a challenge to modern medicine due to the complexity of the neurobiological nerve regenerating process. There is a greater challenge when the transected nerve ends are not amenable to primary end-to-end tensionless neurorraphy. When facing a segmental nerve defect, great effort has been made to develop an alternative to the autologous nerve graft in order to circumvent morbidity at donor site, such as neuroma formation, scarring and permanent loss of function. Tubolization techniques have been developed to bridge nerve gaps and have been extensively studied in numerous experimental and clinical trials. The use of a conduit intends to act as a vehicle for moderation and modulation of the cellular and molecular ambience for nerve regeneration. Among several conduits, vein tubes were validated for clinical application with improving outcomes over the years. This article aims to address the investigation and treatment of segmental nerve injury and draw the current panorama on the use of vein tubes as an autogenous nerve conduit.

Minced nerve tissue in vein grafts used as conduits in rat tibial nerves

INTRODUCTION

Peripheral nerve injuries are encountered frequently in clinical practice. In nerve repair, an end-to-end suture is the preferable choice of treatment. However, where primary closure is not possible, the defect is to be repaired with a nerve graft.

METHODS

A total of 21 female Wistar rats weighing 230 to 290 g were used in the study. They were classified into the following 3 groups: (I) nerve graft, (II) vein graft, and (III) minced nerve graft. In group I, after exposure of the tibial nerve, a 1-cm-long nerve gap was created on the tibial nerve, and the defect was repaired epineurally by using the autogenous nerve. In group II, the 1-cm tibial nerve defect was repaired by using an autogenous vein graft. In group III, a 1-cm nerve graft was divided to 3 equal parts, with one of the nerve parts being minced with microscissors and placed in the vein graft lumen. Thereafter, a 1-cm tibial nerve defect was repaired by the vein graft filled with minced nerve tissue. The tibial function indices (TFIs) were calculated for functional assessment using the Bain-Mackinnon-Hunter formula. Light and electron microscopic evaluations were performed for morphometric assessment. In addition, the myelinated fibers were counted in all groups.

RESULTS

The TFIs of group II were found to be the lowest among all the groups after the sixth week, whereas the TFI of group I was found to be better than the other groups after the sixth week. There was no difference in TFIs between group I and group III. On the basis of the number of myelinated fibers, there was no statistically significant difference between group I and group III, whereas the difference was significant (P<0.05) between groups I/III and group II. Presence of peripheral nerves in light microscopic evaluation revealed normal characteristics of myelinated fibers in all groups. The myelinated axon profile was near normal in the nerve graft group in electron microscopic evaluation. However, there were more degenerated axons with disturbed contours and vacuolizations in the vein graft group compared to the minced nerve graft group.

CONCLUSIONS

We can conclude that using minced nerve tissue in vein grafts as a conduit increases the regeneration of nerves (almost like the nerve graft group) and it may not be caused by donor-site morbidity. It can be used in the repair of nerve defects instead of autogenous nerve grafts after further experimental evidence and clinical trials.

Update on nerve repair by biological tubulization

Many surgical techniques are available for bridging peripheral nerve defects. Autologous nerve grafts are the current gold standard for most clinical conditions. In selected cases, alternative types of conduits can be used. Although most efforts are today directed towards the development of artificial synthetic nerve guides, the use of non-nervous autologous tissue-based conduits (biological tubulization) can still be considered a valuable alternative to nerve autografts. In this paper we will overview the advancements in biological tubulization of nerve defects, with either mono-component or multiple-component autotransplants, with a special focus on the use of a vein segment filled with skeletal muscle fibers, a technique that has been widely investigated in our laboratory and that has already been successfully introduced in the clinical practice.

Bridging peripheral nerve defects with muscle–vein combined guides

Various tubulization techniques can be used to bridge peripheral nerve lesions with substance loss. Among the different materials that have been used so far in alternative to traditional fresh nerve autografts, fresh muscle-vein combined conduits (made by a vein segment filled with fresh skeletal muscle) proved to be particularly effective. In this study, nerve repair of 10-mm long nerve defects by means of muscle-vein combined tubes was compared with repair by means of traditional nerve autografts in the rat sciatic nerve experimental model. Results did not reveal any significant difference between the two groups of regenerated nerves with respect to the total number, mean density and mean size of myelinated nerve fibers. In addition, we also report the results of an experimental study in the rabbit sciatic nerve model, which showed that fresh skeletal muscle enrichment of the vein segment made it possible to bridge 55-mm long nerve gaps. These results provide further evidence of the effectiveness of fresh muscle-vein combined grafts and support the view that this type of conduit can be used also for repairing long nerve gaps.

Construction of tissue engineered nerve grafts and their application in peripheral nerve regeneration

Surgical repair of severe peripheral nerve injuries represents not only a pressing medical need, but also a great clinical challenge. Autologous nerve grafting remains a golden standard for bridging an extended gap in transected nerves. The formidable limitations related to this approach, however, have evoked the development of tissue engineered nerve grafts as a promising alternative to autologous nerve grafts. A tissue engineered nerve graft is typically constructed through a combination of a neural scaffold and a variety of cellular and molecular components. The initial and basic structure of the neural scaffold that serves to provide mechanical guidance and optimal environment for nerve regeneration was a single hollow nerve guidance conduit. Later there have been several improvements to the basic structure, especially introduction of physical fillers into the lumen of a hollow nerve guidance conduit. Up to now, a diverse array of biomaterials, either of natural or of synthetic origin, together with well-defined fabrication techniques, has been employed to prepare neural scaffolds with different structures and properties. Meanwhile different types of support cells and/or growth factors have been incorporated into the neural scaffold, producing unique biochemical effects on nerve regeneration and function restoration. This review attempts to summarize different nerve grafts used for peripheral nerve repair, to highlight various basic components of tissue engineered nerve grafts in terms of their structures, features, and nerve regeneration-promoting actions, and finally to discuss current clinical applications and future perspectives of tissue engineered nerve grafts.

Repairing injured peripheral nerves: Bridging the gap

Peripheral nerve injuries that induce gaps larger than 1-2 cm require bridging strategies for repair. Autologous nerve grafts are still the gold standard for such interventions, although alternative treatments, as well as treatments to improve the therapeutic efficacy of autologous nerve grafting are generating increasing interest. Investigations are still mostly experimental, although some clinical studies have been undertaken. In this review, we aim to describe the developments in bridging technology which aim to replace the autograft. A multi-disciplinary approach is of utmost importance to develop and optimise treatments of the most challenging peripheral nerve injuries.

Transplantation of autologous Schwann cells for the repair of segmental peripheral nerve defects

Peripheral nerve injuries are a source of chronic disability. Incomplete recovery from such injuries results in motor and sensory dysfunction and the potential for the development of chronic pain. The repair of human peripheral nerve injuries with traditional surgical techniques has limited success, particularly when a damaged nerve segment needs to be replaced. An injury to a long segment of peripheral nerve is often repaired using autologous grafting of "noncritical" sensory nerve. Although extensive axonal regeneration can be observed extending into these grafts, recovery of function may be absent or incomplete if the axons fail to reach their intended target. The goal of this review was to summarize the progress that has occurred in developing an artificial neural prosthesis consisting of autologous Schwann cells (SCs), and to detail future directions required in translating this promising therapy to the clinic. In the authors' laboratory, methods are being explored to combine autologous SCs isolated using cell culture techniques with axon guidance channel (AGC) technology to develop the potential to repair critical gap length lesions within the peripheral nervous system. To test the clinical efficacy of such constructs, it is critically important to characterize the fate of the transplanted SCs with regard to cell survival, migration, differentiation, and myelin production. The authors sought to determine whether the use of SC-filled channels is superior or equivalent to strategies that are currently used clinically (for example, autologous nerve grafts). Finally, although many nerve repair paradigms demonstrate evidence of regeneration within the AGC, the authors further sought to determine if the regeneration observed was physiologically relevant by including electrophysiological, behavioral, and pain assessments. If successful, the development of this reparative approach will bring together techniques that are readily available for clinical use and should rapidly accelerate the process of bringing an effective nerve repair strategy to patients with peripheral nerve injury prior to the development of pain and chronic disability.

Chapter 8: Current techniques and concepts in peripheral nerve repair

Despite the progress in understanding the pathophysiology of peripheral nervous system injury and regeneration, as well as advancements in microsurgical techniques, peripheral nerve injuries are still a major challenge for reconstructive surgeons. Thorough knowledge of anatomy, pathophysiology, and surgical reconstruction is a prerequisite of proper peripheral nerve injury management. This chapter reviews the currently available surgical treatment options for different types of nerve injuries in clinical conditions. In overview of direct nerve repair, various end-to-end coaptation techniques and the role of end-to-side repair for proximal nerve injuries is described. When primary repair cannot be performed without undue tension, nerve grafting or tubulization techniques are required. Current gold standard for bridging nerve gaps is nerve autografting. However, disadvantages of this approach, such as donor site morbidity and limited length of available graft material encouraged the search for alternative means of nerve gap reconstruction. Nerve allografting was introduced for repair of extensive nerve injuries. Tubulization techniques with natural or artificial conduits are applicable as an alternative for bridging short nerve defects without the morbidities associated with harvesting of autologous nerve grafts. Achieving better outcomes depends both on the advancements in microsurgical techniques and introduction of molecular biology discoveries into clinical practice. The field of peripheral nerve research is dynamically developing and concentrates on more sophisticated approaches tested at the basic science level. Future directions in peripheral nerve reconstruction including, tolerance induction and minimal immunosuppression for nerve allografting, cell based supportive therapies and bioengineering of nerve conduits are also reviewed in this chapter.

Nerve repair: experimental and clinical evaluation of biodegradable artificial nerve guides

Several methods have been used for bridging nerve gaps. Much of the focus in nerve repair of peripheral nerves has focussed on creating either natural or synthetic tubular nerve guidance channels, as an alternative to nerve autografts. These conduits act to guide axons sprouting from the regenerating nerve end, provide a conduit for diffusion of neurotrophic and neurotropic factors secreted by the injured nerve stump, as well as help protect against infiltration of fibrous tissue. Among the conduits that have been studied are autogenous veins, arteries, mesothelial chambers, synthetic tubes, collagen tubes, amnion tubes, cardiac and skeletal muscle, and silicon tubes. This paper briefly reviews major studies in which bioabsorbable nerve guides were used for peripheral nerve repair, with a particular emphasis on polymeric guidance channels, in an effort to evaluate their use, their ability to support or enhance nerve regeneration and any potential problems.