Viability of cultured nerve grafts: An assessment of proliferation of Schwann cells and fibroblasts

Tissue-engineered nerve guides with mesenchymal stem cells in the facial nerve regeneration

Nerve guides with mesenchymal stem cells have been investigated in the rat facial nerve defect model to promote peripheral nerve regeneration and shorten recovery time to improve patients' quality of life. A 7-mm facial nerve gap experimental rat model is frequently employed in facial nerve regeneration studies. Facial nerve regeneration with nerve guides is evaluated by (1) assessing myelinated fiber counts using toluidine blue staining, (2) immunohistological analysis, (3) determining the g-ratio (axon diameter/total outer diameter) of regenerated nerve on transmission electron microscopic images, (4) retrograde nerve tracing in the facial nucleus, (5) electrophysiological evaluations using compound muscle action potential, and (6) functional evaluations using rat facial palsy scores. Dental pulp and adipose-derived stem cells, easily harvested using a minimally invasive procedure, possess characteristics of mesenchymal tissue lineages and can differentiate into Schwann-like cells. Cultured dental pulp-derived cells can produce neurotrophic factors, including nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor. These neurotrophic factors promote peripheral nerve regeneration and afford protection against facial motor neuron death. Moreover, artificial nerve guides can maneuver axonal regrowth, and dental pulp-derived cells and adipose-derived Schwann cells may supply neurotrophic factors, promoting axonal regeneration. In the present review, the authors discuss facial nerve regeneration using nerve guides with mesenchymal stem cells.

Real-time monitoring of human Schwann cells on heparin-collagen coatings reveals enhanced adhesion and growth factor response

In this work, we evaluate the enhancing effect of six bilayers of heparin/collagen (HEP/COL)₆ layer-by-layer coatings on human Schwann cell (hSCs) adhesion and proliferation in the presence or absence of nerve growth factor (NGF). hSCs behavior and in vitro bioactivity were studied during six days of culture using end-point viability and proliferation assays as well as an impedance-based real-time monitoring system. An end-point viability assay revealed that hSCs cultured on the (HEP/COL)₆ coatings increased their growth by more than 230% compared to controls. However, an EdU proliferation assay revealed that the proliferation rate of hSCs in all conditions were similar, with 45% of cells proliferating after 18 hours of incubation. Fluorescence microscopy revealed that hSCs spreading was similar between the tissue culture plastic control and the (HEP/COL)₆. The presence of NGF in solution resulted in cells with a larger spread area. Real-time monitoring of hSCs seeded on (HEP/COL)₆ with and without NGF reveals that initial cell adhesion is improved by the presence of the (HEP/COL)₆ coatings, and it is further improved by the presence of NGF. Our results suggest that (HEP/COL)₆ coatings enhance Schwann cell behavior and response to NGF. This simple modification could be applied to current nerve regeneration strategies to improve the repair of damaged nerve.

Transplantation effects of dental pulp-derived cells on peripheral nerve regeneration in crushed sciatic nerve injury

The effects of transplanted human dental pulp-derived cells (DPCs) on peripheral nerve regeneration were studied in a rat model of sciatic nerve crush injury. In one group, DPCs were transplanted into the compression site (cell transplantation group); the control group underwent no transplantation (crushed group). Sciatic nerve regeneration was determined based on the recovery of motor function and histological and immunohistochemical analyses. The cell transplantation group showed improved motor function compared with the crushed group using the CatWalk XT system, which corresponded to a higher ratio of tibialis to anterior muscle weight 14 days after surgery. Histological analysis revealed a smaller interspace area and few vacuoles in the sciatic nerve after cell transplantation compared with the crushed group. The myelin sheath was visualized with Luxol Fast Blue (LFB) staining and anti-myelin basic protein (anti-MBP) antibody labeling; the percentages of LFB- and MBP-positive areas were higher in the cell transplantation group than in the crushed group. Human mitochondria-positive cells were also identified in the sciatic nerve at the transplantation site 14 days after surgery. Taken together, the observed correlation between morphological findings and functional outcomes following DPC transplantation indicates that DPCs promote peripheral nerve regeneration in rats.

Synthetic bioresorbable poly-α-hydroxyesters as peripheral nerve guidance conduits; a review of material properties, design strategies and their efficacy to date

Implantable tubular devices known as nerve guidance conduits (NGCs) have drawn considerable interest as an alternative to autografting in the repair of peripheral nerve injuries.

Effects of nerve cells and adhesion molecules on nerve conduit for peripheral nerve regeneration

Background

For peripheral nerve regeneration, recent attentions have been paid to the nerve conduits made by tissue-engineering technique. Three major elements of tissue-engineering are cells, molecules, and scaffolds.

Methods

In this study, the attachments of nerve cells, including Schwann cells, on the nerve conduit and the effects of both growth factor and adhesion molecule on these attachments were investigated.

Results

The attachment of rapidly-proliferating cells, C6 cells and HS683 cells, on nerve conduit was better than that of slowly-proliferating cells, PC12 cells and Schwann cells, however, the treatment of nerve growth factor improved the attachment of slowly-proliferating cells. In addition, the attachment of Schwann cells on nerve conduit coated with fibronectin was as good as that of Schwann cells treated with glial cell line-derived neurotrophic factor (GDNF).

Conclusions

Growth factor changes nerve cell morphology and affects cell cycle time. And nerve growth factor or fibronectin treatment is indispensable for Schwann cell to be used for implantation in artificial nerve conduits.

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.

Electrophysiologic and functional evaluations of regenerated facial nerve defects with a tube containing dental pulp cells in rats

BACKGROUND

Dental pulp tissue contains Schwann and neural progenitor cells. Tissue-engineered nerve conduits with dental pulp cells promote facial nerve regeneration in rats. However, no nerve functional or electrophysiologic evaluations were performed. This study investigated the compound muscle action potential recordings and facial functional analysis of dental pulp cell regenerated nerve in rats.

METHODS

A silicone tube containing rat dental pulp cells in type I collagen gel was transplanted into a 7-mm gap of the buccal branch of the facial nerve in Lewis rats; the same defect was created in the marginal mandibular branch, which was ligatured. Compound muscle action potential recordings of vibrissal muscles and facial functional analysis with facial palsy score of the nerve were performed.

RESULTS

Tubulation with dental pulp cells showed significantly lower facial palsy scores than the autograft group between 3 and 10 weeks postoperatively. However, the dental pulp cell facial palsy scores showed no significant difference from those of autograft after 11 weeks. Amplitude and duration of compound muscle action potentials in the dental pulp cell group showed no significant difference from those of the intact and autograft groups, and there was no significant difference in the latency of compound muscle action potentials between the groups at 13 weeks postoperatively. However, the latency in the dental pulp cell group was prolonged more than that of the intact group.

CONCLUSION

Tubulation with dental pulp cells could recover facial nerve defects functionally and electrophysiologically, and the recovery became comparable to that of nerve autografting in rats.

Effects of cerebrolysin on rat Schwann cells in vitro

Although the peripheral nervous system (PNS) is capable of regeneration, these processes are limited. As a potential means to augment PNS regeneration, the effects of cerebrolysin (CL), a proteolytic peptide fraction, were tested in vitro on Schwann cell (SC) proliferation, stress resistance, phagocytic and cluster-forming capacity. Primary SC/fibrocyte co-cultures were prepared from dorsal root ganglia of 5-7-day-old rats. SCs were subjected to mechanical stress by media change and metabolic stress by serum glucose deprivation (SGD). Cell survival was assessed using MTT test. SC proliferation was determined by counting BrdU-labeled cells. SC clustering was studied by ImageJ analysis of S100 immunostaining. Wallerian degeneration (WD) was evaluated by measuring acetylcholine-esterase staining within sciatic nerves in vitro. It was found that CL caused no effect on MTT turnover in the tested doses. CL inhibited SC proliferation in a dose-dependent manner. Media change and additional SGD stress inhibited SC clustering. CL enhanced the reorganization of SC clusters and was able to counteract SGD-induced cluster defects. Moreover, CL accelerated WD in vitro. CL was able to enhance the functions of SCs that are relevant to nerve regeneration. Thus, our findings suggest that CL may be suitable for therapeutic usage to enhance PNS regeneration/reconstruction.

Detection of subtle neurological alterations by the Catwalk XT gait analysis system

BACKGROUND

A new version of the CatWalk XT system was evaluated as a tool for detecting very subtle alteration in gait based on higher speed sample rate; the system could also demonstrate minor changes in neurological function. In this study, we evaluated the neurological outcome of sciatic nerve injury intervened by local injection of hyaluronic acid. Using the CatWalk XT system, we looked for differences between treated and untreated groups and differences within the same group as a function of time so as to assess the power of the Catwalk XT system for detecting subtle neurological change.

METHODS

Peripheral nerve injury was induced in 36 Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. The animals were randomized into one of two groups: Group I: crush injury as the control; Group II: crush injury and local application with hyaluronic acid. These animals were subjected to neurobehavior assessment, histomorphology evaluation, and electrophysiology study periodically. These data were retrieved for statistical analysis.

RESULTS

The density of neurofilament and S-100 over the distal end of crushed nerve showed significant differences either in inter-group comparison at various time points or intra-group comparison from 7 to 28 days. Neuronal structure architecture, axon counts, intensity of myelination, electrophysiology, and collagen deposition demonstrate significant differences between the two groups. There was significant difference of SFI and angle of ankle in inter- group analysis from 7 to 28 days, but there were no significant differences in SFI and angle of ankle at time points of 7 and 14 days. In the Cat Walk XT analysis, the intensity, print area, stance duration, and swing duration all showed detectable differences at 7, 14, 21, and 28 days, whereas there were no significant difference at 7 and 14 days with CatWalk 7 testing. In addition, there were no significant differences of step sequence or regularity index between the two versions.

CONCLUSION

Hyaluronic acid augmented nerve regeneration as early as 7 days after crush injury. This subtle neurological alteration could be detected through the CatWalk XT gait analysis but not the SFI, angle of ankle, or CatWalk 7 methods.

The behavior of neuronal cells on tendon-derived collagen sheets as potential substrates for nerve regeneration

Peripheral nervous system injuries result in a decreased quality of life, and generally require surgical intervention for repair. Currently, the gold standard of nerve autografting, based on the use of host tissue such as sensory nerves is suboptimal as it results in donor-site loss of function and requires a secondary surgery. Nerve guidance conduits fabricated from natural polymers such as collagen are a common alternative to bridge nerve defects. In the present work, tendon sections derived through a process named bioskiving were studied for their potential for use as a substrate to fabricate nerve guidance conduits. We show that cells such as rat Schwann cells adhere, proliferate, and align along the fibrous tendon substrate which has been shown to result in a more mature phenotype. Additionally we demonstrate that chick dorsal root ganglia explants cultured on the tendon grow to similar lengths compared to dorsal root ganglia cultured on collagen gels, but also grow in a more oriented manner on the tendon sections. These results show that tendon sections produced through bioskiving can support directional nerve growth and may be of use as a substrate for the fabrication of nerve guidance conduits.

Mesenchymal stem cells in a polycaprolactone conduit promote sciatic nerve regeneration and sensory neuron survival after nerve injury

Despite the fact that the peripheral nervous system is able to regenerate after traumatic injury, the functional outcomes following damage are limited and poor. Bone marrow mesenchymal stem cells (MSCs) are multipotent cells that have been used in studies of peripheral nerve regeneration and have yielded promising results. The aim of this study was to evaluate sciatic nerve regeneration and neuronal survival in mice after nerve transection followed by MSC treatment into a polycaprolactone (PCL) nerve guide. The left sciatic nerve of C57BL/6 mice was transected and the nerve stumps were placed into a biodegradable PCL tube leaving a 3-mm gap between them; the tube was filled with MSCs obtained from GFP+ animals (MSC-treated group) or with a culture medium (Dulbecco's modified Eagle's medium group). Motor function was analyzed according to the sciatic functional index (SFI). After 6 weeks, animals were euthanized, and the regenerated sciatic nerve, the dorsal root ganglion (DRG), the spinal cord, and the gastrocnemius muscle were collected and processed for light and electron microscopy. A quantitative analysis of regenerated nerves showed a significant increase in the number of myelinated fibers in the group that received, within the nerve guide, stem cells. The number of neurons in the DRG was significantly higher in the MSC-treated group, while there was no difference in the number of motor neurons in the spinal cord. We also found higher values of trophic factors expression in MSC-treated groups, especially a nerve growth factor. The SFI revealed a significant improvement in the MSC-treated group. The gastrocnemius muscle showed an increase in weight and in the levels of creatine phosphokinase enzyme, suggesting an improvement of reinnervation and activity in animals that received MSCs. Immunohistochemistry documented that some GFP+ -transplanted cells assumed a Schwann-cell-like phenotype, as evidenced by their expression of the S-100 protein, a Schwann cell marker. Our findings suggest that using a PCL tube filled with MSCs is a good strategy to improve nerve regeneration after a nerve transection in mice.

Dual regeneration of muscle and nerve by intravenous administration of human amniotic fluid-derived mesenchymal stem cells regulated by stromal cell-derived factor-1α in a sciatic nerve injury model

OBJECT

Human amniotic fluid-derived mesenchymal stem cells (AFMSCs) have been shown to promote peripheral nerve regeneration. The expression of stromal cell-derived factor-1α (SDF-1α) in the injured nerve exerts a trophic effect by recruiting progenitor cells that promote nerve regeneration. In this study, the authors investigated the feasibility of intravenous administration of AFMSCs according to SDF-1α expression time profiles to facilitate neural regeneration in a sciatic nerve crush injury model.

METHODS

Peripheral nerve injury was induced in 63 Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. The animals were randomized into 1 of 3 groups: Group I, crush injury as the control; Group II, crush injury and intravenous administration of AFMSCs (5 × 10(6) cells for 3 days) immediately after injury (early administration); and Group III, crush injury and intravenous administration of AFMSCs (5 × 10(6) cells for 3 days) 7 days after injury (late administration). Evaluation of neurobehavior, electrophysiological study, and assessment of regeneration markers were conducted every week after injury. The expression of SDF-1α and neurotrophic factors and the distribution of AFMSCs in various time profiles were also assessed.

RESULTS

Stromal cell-derived factor-1α increased the migration and wound healing of AFMSCs in vitro, and the migration ability was dose dependent. Crush injury induced the expression of SDF-1α at a peak of 10-14 days either in nerve or muscle, and this increased expression paralleled the expression of its receptor, chemokine receptor type-4 (CXCR-4). Most AFMSCs were distributed to the lung during early or late administration. Significant deposition of AFMSCs in nerve and muscle only occurred in the late administration group. Significantly enhanced neurobehavior, electrophysiological function, nerve myelination, and expression of neurotrophic factors and acetylcholine receptor were demonstrated in the late administration group.

CONCLUSIONS

Amniotic fluid-derived mesenchymal stem cells can be recruited by expression of SDF-1α in muscle and nerve after nerve crush injury. The increased deposition of AFMSCs paralleled the expression profiles of SDF-1α and its receptor CXCR-4 in either muscle or nerve. Administration of AFMSCs led to improvements in neurobehavior and expression of regeneration markers. Intravenous administration of AFMSCs may be a promising alternative treatment strategy in peripheral nerve disorder.

Recruitment by SDF-1α of CD34-positive cells involved in sciatic nerve regeneration

Object

Increased integration of CD34+ cells in injured nerve significantly promotes nerve regeneration, but this effect can be counteracted by limited migration and short survival of CD34+ cells. SDF-1α and its receptor mediate the recruitment of CD34+ cells involved in the repair mechanism of several neurological diseases. In this study, the authors investigate the potentiation of CD34+ cell recruitment triggered by SDF-1α and the involvement of CD34+ cells in peripheral nerve regeneration.

Methods

Peripheral nerve injury was induced in 147 Sprague-Dawley rats by crushing the left sciatic nerve with a vessel clamp. The animals were allocated to 3 groups: Group 1, crush injury (controls); Group 2, crush injury and local application of SDF-1α recombinant proteins; and Group 3, crush injury and local application of SDF-1α antibody. Electrophysiological studies and assessment of regeneration markers were conducted at 4 weeks after injury; neurobehavioral studies were conducted at 1, 2, 3, and 4 weeks after injury. The expression of SDF-1α, accumulation of CD34+ cells, immune cells, and angiogenesis factors in injured nerves were evaluated at 1, 3, 7, 10, 14, 21, and 28 days after injury.

Results

Application of SDF-1α increased the migration of CD34+ cells in vitro, and this effect was dose dependent. Crush injury induced the expression of SDF-1α, with a peak of 10–14 days postinjury, and this increased expression of SDF-1α paralleled the deposition of CD34+ cells, expression of VEGF, and expression of neurofilament. These effects were further enhanced by the administration of SDF-1α recombinant protein and abolished by administration of SDF-1α antibody. Furthermore, these effects were consistent with improvement in measures of neurological function such as sciatic function index, electrophysiological parameters, muscle weight, and myelination of regenerative nerve.

Conclusions

Expression of SDF-1α facilitates recruitment of CD34+ cells in peripheral nerve injury. The increased deposition of CD34+ cells paralleled significant expression of angiogenesis factors and was consistent with improvement of neurological function. Utilization of SDF-1α for enhancing the recruitment of CD34+ cells involved in peripheral nerve regeneration may be considered as an alternative treatment strategy in peripheral nerve disorders.

Schwann cell metabolic activity in various short-term holding conditions: implications for improved nerve graft viability

Strategies for improvement of nerve regeneration and optimal conditions to prevent Schwann cell (SC) loss within a nerve transplant procedure are critical. The purpose of this study was to examine SC viability, which plays an important role in peripheral nerve regeneration, under various incubation conditions up to three hours. To address this issue, Schwann cell metabolic activity was determined using different independent test methods. The following experimental conditions were compared: SCs prepared from nerves were incubated in (1) isotonic saline solution (2) Dulbecco's modified Eagles medium as used for cell culturing, (3) Hannover bioreactor medium, and (4) Leibovitz's medium. SC metabolic activity of excised rat sciatic nerve was determined at 4°C, 18°C, and 37°C over 3 hrs. The results indicate that SC activity was optimized by the usage of Leibovitz's medium or HBRM at 37°C. Greater SC viability at the time of surgical nerve grafting could contribute to improved axonal regeneration and remyelination after nerve transplantation, and thus more successful functional recovery.

In vivo MR imaging tracking of transplanted mesenchymal stem cells in a rabbit model of acute peripheral nerve traction injury

PURPOSE

To investigate in vivo MRI tracking mesenchymal stem cells (MSCs) in peripheral nerve injures using a clinically available paramagnetic contrast agent (Gd-DTPA) and commercially available rhodamine-incorporated transfection reagents (PEI-FluoR).

MATERIALS AND METHODS

After bone marrow MSCs were labeled with Gd-DTPA and PEI-FluoR complex, the labeling efficacy and longevity of Gd-DTPA maintenance were measured and cell viability, proliferation, and apoptosis were assessed. Thirty-six rabbits with acute sciatic nerve traction injury randomly received 1 × 10(6) labeled (n = 12) or unlabeled MSCs (n = 12) or vehicle alone injection. The distribution and migration of implanted cells was followed by MRI and correlated with histology. The relative signal intensity (RSL) of the grafts was measured.

RESULTS

The labeling efficiency was 76 ± 4.7% and the labeling procedure did not influence cell viability, proliferation, and apoptosis. A persistent higher RSL in grafts was found in the labeled group compared with the unlabeled and vehicle groups until 10 days after transplantation (P < 0.05). The distribution and migration of labeled cells could be tracked by MRI until 10 days after transplantation. Transplanted MSCs were not found to transdifferentiate into Schwann-like cells within 14-day follow-up.

CONCLUSION

Labeling MSCs with the dual agents may enable cellular MRI of the engraftment in the experimental peripheral nerve injury.

PLGA artificial nerve conduits with dental pulp cells promote facial nerve regeneration

A number of recent studies have shown the effectiveness of tubulation, using neural progenitor cells or Schwann cells, for promoting nerve regeneration. However, the use of neural cells from other neural donor tissues has potentially serious clinical complications. Therefore, we focused on dental pulp as a new cell source for use in such artificial conditions. Previously, we showed that silicone tubes filled with dental pulp cells (DPCs) promoted facial nerve regeneration in rats. However, the use of silicone tubes requires a secondary removal operation because they may give rise to chronic inflammation and pain. Therefore, to avoid this procedure, a new artificial device was prepared from a degradable poly-DL-lactide-co-glycolide (PLGA) tube containing DPCs, and its effectiveness for repairing gaps in the facial nerves of rats was investigated. A PLGA tube containing rat DPCs embedded in a collagen gel was transplanted into a gap in a rat facial nerve. Five days after transplantation, the facial nerves connected by the PLGA tubes containing DPCs were repaired more quickly than the control nerves. The PLGA tubes were resorbed in vivo and nerve regeneration was observed 2 months after the transplantation. Immunostaining showed that Tuj1-positive axons were present in the regenerated nerves 2 months after transplantation, and osmium-toluidine blue staining showed no mineralization of the regenerated nerves in those tubes containing myelinated fibres after 9 weeks. PLGA tubes filled with DPCs promoted nerve regeneration and were readily resorbed in vivo.

Enhancement of regeneration with glia cell line-derived neurotrophic factor-transduced human amniotic fluid mesenchymal stem cells after sciatic nerve crush injury

OBJECT

Human amniotic fluid-derived mesenchymal stem cells (AFMSCs) have been shown to promote peripheral nerve regeneration, and the local delivery of neurotrophic factors may additionally enhance nerve regeneration capacity. The present study evaluates whether the transplantation of glia cell line-derived neurotrophic factor (GDNF)-modified human AFMSCs may enhance regeneration of sciatic nerve after a crush injury.

METHODS

Peripheral nerve injury was produced in Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. Either GDNF-modified human AFMSCs or human AFMSCs were embedded in Matrigel and delivered to the injured nerve. Motor function and electrophysiological studies were conducted after 1 and 4 weeks. Early or later nerve regeneration markers were used to evaluate nerve regeneration. The expression of GDNF in the transplanted human AFMSCs and GDNF-modified human AFMSCs was monitored at 7-day intervals.

RESULTS

Human AFMSCs were successfully transfected with adenovirus, and a significant amount of GDNF was detected in human AFMSCs or the culture medium supernatant. Increases in the sciatic nerve function index, the compound muscle action potential ratio, conduction latency, and muscle weight were found in the groups treated with human AFMSCs or GDNF-modified human AFMSCs. Importantly, the GDNF-modified human AFMSCs induced the greatest improvement. Expression of markers of early nerve regeneration, such as increased expression of neurofilament and BrdU and reduced Schwann cell apoptosis, as well as late regeneration markers, consisting of reduced vacuole counts, increased expression of Luxol fast blue and S100 protein, paralleled the results of motor function. The expression of GDNF in GDNF-modified human AFMSCs was demonstrated up to 4 weeks; however, the expression decreased over time.

CONCLUSIONS

The GDNF-modified human AFMSCs appeared to promote nerve regeneration. The consecutive expression of GDNF was demonstrated in GDNF-modified human AFMSCs up to 4 weeks. These findings support a nerve regeneration scenario involving cell transplantation with additional neurotrophic factor secretion.

Escalated regeneration in sciatic nerve crush injury by the combined therapy of human amniotic fluid mesenchymal stem cells and fermented soybean extracts, Natto

Attenuation of inflammatory cell deposits and associated cytokines prevented the apoptosis of transplanted stem cells in a sciatic nerve crush injury model. Suppression of inflammatory cytokines by fermented soybean extracts (Natto) was also beneficial to nerve regeneration. In this study, the effect of Natto on transplanted human amniotic fluid mesenchymal stem cells (AFS) was evaluated. Peripheral nerve injury was induced in SD rats by crushing a sciatic nerve using a vessel clamp. Animals were categorized into four groups: Group I: no treatment; Group II: fed with Natto (16 mg/day for 7 consecutive days); Group III: AFS embedded in fibrin glue; Group IV: Combination of group II and III therapy. Transplanted AFS and Schwann cell apoptosis, inflammatory cell deposits and associated cytokines, motor function, and nerve regeneration were evaluated 7 or 28 days after injury. The deterioration of neurological function was attenuated by AFS, Natto, or the combined therapy. The combined therapy caused the most significantly beneficial effects. Administration of Natto suppressed the inflammatory responses and correlated with decreased AFS and Schwann cell apoptosis. The decreased AFS apoptosis was in line with neurological improvement such as expression of early regeneration marker of neurofilament and late markers of S-100 and decreased vacuole formation. Administration of either AFS, or Natto, or combined therapy augmented the nerve regeneration. In conclusion, administration of Natto may rescue the AFS and Schwann cells from apoptosis by suppressing the macrophage deposits, associated inflammatory cytokines, and fibrin deposits.

Human amniotic fluid mesenchymal stem cells in combination with hyperbaric oxygen augment peripheral nerve regeneration

PURPOSE

Attenuation of pro-inflammatory cytokines and associated inflammatory cell deposits rescues human amniotic fluid mesenchymal stem cells (AFS) from apoptosis. Hyperbaric oxygen (HBO) suppressed stimulus-induced pro-inflammatory cytokine production in blood-derived monocyte-macrophages. Herein, we evaluate the beneficial effect of hyperbaric oxygen on transplanted AFS in a sciatic nerve injury model.

METHODS

Peripheral nerve injury was produced in Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. The AFS were embedded in fibrin glue and delivered to the injured site. Hyperbaric oxygen (100% oxygen, 2 ATA, 60 min/day) was administered 12 h after operation for seven consecutive days. Transplanted cell apoptosis, oxidative stress, inflammatory cell deposits and associated chemokines, pro-inflammatory cytokines, motor function, and nerve regeneration were evaluated 7 and 28 days after injury.

RESULTS

Crush injury induced an inflammatory response, disrupted nerve integrity, and impaired nerve function in the sciatic nerve. However, crush injury-provoked inflammatory cytokines, deposits of inflammatory cytokines, and associated macrophage migration chemokines were attenuated in groups receiving hyperbaric oxygen but not in the AFS-only group. No significant increase in oxidative stress was observed after administration of HBO. In transplanted AFS, marked apoptosis was detected and this event was reduced by HBO treatment. Increased nerve myelination and improved motor function were observed in AFS-transplant, HBO-administrated, and AFS/HBO-combined treatment groups. Significantly, the AFS/HBO combined treatment showed the most beneficial effect.

CONCLUSION

AFS in combination with HBO augment peripheral nerve regeneration, which may involve the suppression of apoptotic death in implanted AFS and the attenuation of an inflammatory response detrimental to peripheral nerve regeneration.

Tubulation with dental pulp cells promotes facial nerve regeneration in rats

Dental pulp is an easily obtainable source of viable cells for potential use in peripheral nerve regeneration. We prepared artificial conditions for nerve regeneration using a silicone tube containing a collagen gel embedded with rat dental pulp cells, and we examined its effectiveness for repairing a gap in the rat facial nerve. Twelve days after transplantation, defective facial nerves connected with silicone tubes containing dental pulp cells were repaired more rapidly than control tubes containing the collagen gel alone. When a tube containing green fluorescent protein (GFP)-positive dental pulp cells was transplanted into a facial nerve gap in a GFP-negative rat, we observed regenerated nerves with GFP-positive cells at 2 weeks posttransplantation. The regenerated nerves included Tuj1-positive axons, RECA1 and GFP double-positive blood vessels, and S100 and GFP double-positive Schwann-like supportive cells. Osmium-toluidine blue staining revealed that the regenerated nerves contained myelinated fibers. Moreover, fluorescent retrograde tracing analysis by application of Fluoro-Gold into the regenerated nerves demonstrated the presence of Fluoro-Gold-positive motor neurons in the facial nucleus of the rat brain. These results suggest that the transplanted dental pulp cells formed blood vessels and myelinating tissue and contributed to the promotion of normal nerve regeneration.

Combination of G-CSF administration and human amniotic fluid mesenchymal stem cell transplantation promotes peripheral nerve regeneration

Amniotic fluid mesenchymal stem cells (AFS) harbor the potential to improve peripheral nerve injury by inherited neurotrophic factor secretion, but present the drawback of the short-term survival after transplantation. Granulocyte-colony stimulating factor (G-CSF) has a diversity of functions, including anti-inflammatory and anti-apoptotic effects. This study was conducted to evaluate whether G-CSF could augment the neuroprotective effect of transplanted AFS against peripheral nerve injury. The potential involvement of anti-inflammation/anti-apoptosis effect was also investigated. Peripheral nerve injury was produced in Sprauge-Dawley rats by crushing left sciatic nerve using a vessel clamp. The AFS were embedded in fibrin glue and delivered to the injured site. G-CSF (50 microg/kg) was administrated by intra-peritoneal injection for 7 consecutive days. Cell apoptosis, inflammatory cytokines, motor function, and nerve regeneration were evaluated 7 or 28 days after injury. Crush injury induced inflammatory response, disrupted nerve integrity, and impaired nerve function in sciatic nerve. Crush injury-provoked inflammation was attenuated in groups receiving G-CSF but not in AFS only group. In transplanted AFS, marked apoptosis was detected and this event was reduced by G-CSF treatment. Increased nerve myelination and improved motor function were observed in AFS transplanted, G-CSF administrated, and AFS/G-CSF combined treatment groups. Significantly, the combined treatment showed the most beneficial effect. In conclusion, the concomitant treatment of AFS with G-CSF augments peripheral nerve regeneration which may involve the suppression of apoptotic death in implanted AFS and the attenuation of inflammatory response.

Peripheral nerve regeneration using a three dimensionally cultured schwann cell conduit

The use of artificial nerve conduit containing viable Schwann cells is one of the most promising strategies to repair peripheral nerve injury. To fabricate an effective nerve conduit whose microstructure and internal environment are more favorable in nerve regeneration than those currently existing, a new three-dimensional (3D) Schwann cell culture technique using Matrigel and dorsal root ganglion (DRG) was developed. Nerve conduit of 3D arranged Schwann cells was fabricated using direct seeding of freshly harvested DRG into Matrigel-filled silicone tubes (inner diameter 1.98 mm, 14 mm length) and in vitro rafting culture for 2 weeks. The nerve regeneration efficacy of 3D cultured Schwann cell conduit (3D conduit group, n = 6) was assessed using an Sprague-Dawley rat sciatic nerve defect of 10 mm and compared with that of a silicone conduit filled with Matrigel and Schwann cells prepared with the conventional plain culture method (two-dimensional [2D] conduit group, n = 6). After 12 weeks, sciatic function was evaluated with sciatic function index (SFI) and gait analysis, and histomorphology of nerve conduit and the innervated tissues of sciatic nerve were examined using image analyzer and electromicroscopic methods. The SFI and ankle stance angle in the functional evaluation were -60.1 +/- 13.9, 37.9 degrees +/- 5.4 degrees in the 3D conduit group (n = 5) and -87.0 +/- 12.9, 32.2 degrees +/- 4.8 degrees in the 2D conduit group (n = 4). The myelinated axon was 44.91% +/- 0.13% in the 3D conduit group and 13.05% +/- 1.95% in the 2D conduit group. In the transmission electron microscope study, the 3D conduit group showed more abundant myelinated nerve fibers with well-organized and thickened extracellular collagen than the 2D conduit group, and the gastrocnemius muscle and biceps femoris tendon in the 3D conduit group were less atrophied and showed decreased fibrosis with less fatty infiltration than the 2D conduit group. A new 3D Schwann cell culture technique was established, and nerve conduit fabricated using this technique showed much improved nerve regeneration capacity than the silicone tube filled with Matrigel and Schwann cells prepared from the conventional plain culture method.

Transplantation of bone marrow stromal cells for peripheral nerve repair

Cell transplantation using bone marrow stromal cells (BMSCs) to alleviate neurological deficits has recently become the focus of research in regenerative medicine. Evidence suggests that secretion of various growth-promoting substances likely plays an important role in functional recovery against neurological diseases. In an attempt to identify a possible mechanism underlying the regenerative potential of BMSCs, this study investigated the production and possible contribution of neurotrophic factors by transected sciatic nerve defect in a rat model with a 15 mm gap. Cultured BMSCs became morphologically homogeneous with fibroblast-like shape after ex vivo expansion. We provided several pieces of evidence for the beneficial effects of implanted fibroblast-like BMSCs on sciatic nerve regeneration. When compared to silicone tube control animals, this treatment led to (i) improved walking behavior as measured by footprint analysis, (ii) reduced loss of gastrocnemius muscle weight and EMG magnitude, and (iii) greater number of regenerating axons within the tube. Cultured fibroblast-like BMSCs constitutively expressed trophic factors and supporting substances, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF), collagen, fibronectin, and laminin. The progression of the regenerative process after BMSC implantation was accompanied by elevated expression of neurotrophic factors at both early and later phases. These results taken together, in addition to documented Schwann cell-like differentiation, provide evidence indicating the strong association of neurotrophic factor production and the regenerative potential of implanted BMSCs.

Effects of unidirectional permeability in asymmetric poly(DL-lactic acid-co-glycolic acid) conduits on peripheral nerve regeneration: Anin vitro andin vivo study

The high outflow permeability of the nerve conduit used to emit the drained waste generated from the traumatized host nerve stump is critical in peripheral nerve regeneration. Our earlier studies have established that asymmetric conduits fulfill the basic requirements for use as nerve guide conduits. In this study, the inflow characteristics of optimal nerve conduits were further examined using in vivo and in vitro trials. Various asymmetric poly(DL-lactic acid-co-glycolic acid) (PLGA) conduits were controlled by modifying precipitation baths using 0, 20, and 95% isopropyl alcohol, with high-porosity (permeability), medium-porosity (high outflow and low inflow), and low-porosity (permeability), respectively. In the in vitro trial, the Schwann cells and fibroblasts were seeded on either side of the asymmetric PLGA films in a newly designed coculture system that simulated the repaired nerve conduit environment. The results of the directional permeable films indicated the statistically significant proliferation of Schwann cells and the inhibition of the division of fibroblasts in lactate dehydrogenase release and inhibition of 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide (MTT) reduction, compared with the other films. In the in vivo trial, the PLGA conduits seeded with Schwann cells were implanted into 10 mm right sciatic nerve defects in rats. After 6 weeks, implanted conduits were harvested. Histological examination verified that directional permeable conduits had markedly more A-type and B-type myelin fibers in the midconduit and distal nerve. In this work, the directional transport characteristics were established as an extremely important factor to the design and development of optimal nerve guide conduits in peripheral nerve regeneration.

Adhesion and proliferation of human Schwann cells on adhesive coatings

Attachment to and proliferation on the substrate are deemed important considerations when Schwann cells (SCs) are to be seeded in synthetic nerve grafts. Attachment is a prerequisite for the SCs to survive and fast proliferation will yield large numbers of SCs in a short time, which appears promising for stimulation of peripheral nerve regeneration. The aim of the present study was to compare the adhesion and proliferation of human Schwann cells (HSCs) on different substrates. The following were selected for their suitability as an internal coating of synthetic nerve grafts; the extracellular matrix proteins fibronectin, laminin and collagen type I and the poly-electrolytes poly(d-lysine) (PDL) and poly(ethylene-imine) (PEI). On all coatings, attachment of HSCs was satisfactory and comparable, indicating that this factor is not a major consideration in choosing a suitable coating. Proliferation was best on fibronectin, laminin and PDL, and worst on collagen type I and PEI. Since nerve regeneration is enhanced by laminin and/or fibronectin, these are preferred as coatings for synthetic nerve grafts seeded with SCs.

Multidimensional long-term time-lapse microscopy of in vitro peripheral nerve regeneration

In order to test the effectiveness of a new advanced time-lapse microscopy imaging and image processing and analysis system, and to do quantitative and qualitative temporal analyses of in vitro peripheral nerve regeneration, long-term time-lapse imaging of cultures of mouse dorsal root ganglia (DRGs) was performed. DRGs were placed in a Petri dish, covered with collagen gel, their attached peripheral nerves were cut in the middle, creating a gap, and the dish was filled with culture medium. Six preparations were kept on the time-lapse imaging system, which provides a suitable incubation environment and enables to capture images from multiple coordinates at x,y,z axes at desired time intervals for 13 days. In general, the time-lapse imaging system proved quite stable and efficient, although some improvements are certainly required. Two main components of peripheral nerve regeneration, outgrowth of axons and activities of resident cells, were examined. Axons started to grow during the first hour of incubation with a 16.5 microm/h rate and showed the slowest rates (0.7 microm/h) on days 8 and 9, after which they resumed higher speeds again. The first cell came out of the proximal end of the cut nerve on the second day and it was a Schwann cell (SC), which was the prominent cell type in the preparations throughout the experiment. SCs were higher in number (83.15% of all cells) but slower in migration (3.4 vs. 7.3 microm/h, P < 0.001) than other cells. Other observed characteristics of axonal outgrowth and cellular activity and interactions between axons and the cells are discussed.

Metalloproteinase-dependent predegeneration in vitro enhances axonal regeneration within acellular peripheral nerve grafts

Injury to peripheral nerve initiates a degenerative process that converts the denervated nerve from a suppressive environment to one that promotes axonal regeneration. We investigated the role of matrix metalloproteinases (MMPs) in this degenerative process and whether effective predegenerated nerve grafts could be produced in vitro. Rat peripheral nerve explants were cultured for 1-7 d in various media, and their neurite-promoting activity was assessed by cryoculture assay, in which neurons are grown directly on nerve sections. The neurite-promoting activity of cultured nerves increased rapidly and, compared with uncultured nerve, a maximum increase of 72% resulted by 2 d of culture in the presence of serum. Remarkably, the neurite-promoting activity of short-term cultured nerves was also significantly better than nerves degenerated in vivo. We examined whether in vitro degeneration is MMP dependent and found that the MMP inhibitor N-[(2R)-2(hydroxamidocarbonylmethyl)-4-methylpantanoyl]-l-tryptophan methylamide primarily blocked the degenerative increase in neurite-promoting activity. In the absence of hematogenic macrophages, MMP-9 was trivial, whereas elevated MMP-2 expression and activation paralleled the increase in neurite-promoting activity. MMP-2 immunoreactivity localized to Schwann cells and the endoneurium and colocalized with gelatinolytic activity as demonstrated by in situ zymography. Finally, in vitro predegenerated nerves were tested as acellular grafts and, compared with normal acellular nerve grafts, axonal ingress in vivo was approximately doubled. We conclude that Schwann cell expression of MMP-2 plays a principal role in the degenerative process that enhances the regeneration-promoting properties of denervated nerve. Combined with their low immunogenicity, acellular nerve grafts activated by in vitro predegeneration may be a significant advancement for clinical nerve allografting.

A Schwann cell-seeded intrinsic framework and its satisfactory biocompatibility for a bioartificial nerve graft

To optimize the internal environment of a collagen nerve tube, we designed a Schwann cell-seeded intrinsic framework and its biocompatibility was investigated. We fixed 6-0 polyglactin woven filaments (Vicryl) or polydioxanone monofilaments (PDS) on a silicone ring in a net fashion. It was coated with matrigel and then incubated with cultured newborn or adult Schwann cells. Furthermore, we implanted 1.5-cm-long filament-filled collagen tubes in a rat model. Using a live/dead fluorescent assay and electron microscopy, we found that adherent Schwann cells onto filaments remained viable and oriented longitudinally along filaments. The preliminary in vivo study indicated that a mild inflammatory reaction was present around the tube wall. However, nerve regeneration occurred around and between filaments. We concluded that the arrangement of Schwann cell columns onto filaments was achieved, mimicking Bünger bands. It was shown that the biomaterials did not impede nerve regeneration.