Neuroregenerative Effects of Preinjury FK-506 Administration

Interpretation of Data from Translational Rodent Nerve Injury and Repair Models

This article highlights the use of rodents as preclinical models to evaluate the management of nerve injuries, describing the pitfalls and value from rodent nerve injury and regeneration outcomes, as well as treatments derived from these rodent models. The anatomic structure, size, and cellular and molecular differences and similarities between rodent and human nerves are summarized. Specific examples of success and failure when assessing outcome metrics are presented for context. Evidence for translation to clinical practice includes the topics of electrical stimulation, Tacrolimus (FK506), and acellular nerve allografts.

Adipose-Derived Stem Cells and Tacrolimus Improve Nerve Regeneration in a Rat Sciatic Nerve Defect Model

This study compared the effect of undifferentiated adipose-derived stem cells (ADSCs) vs tacrolimus (FK506) in peripheral nerve regeneration in a rat sciatic nerve complete transection model. Forty Wistar rats were equally distributed in four groups. In the SHAM surgery group, the sciatic nerve was exposed and no further intervention was done. In the conduit-alone group (the SLN group), a 10-mm nerve gap was created and bridged with a fibrin conduit filled in with normal saline. In the FK506 group, the fibrin conduit was injected with soluble FK506. In the ADSC group, the conduit was impregnated with undifferentiated ADSCs. Nerve regeneration was assessed by means of walking track analysis, electromyography, and neurohistomorphometry. Clinically and microscopically, nerve regeneration was achieved in all groups at 12 weeks. Walking track analysis confirmed functional recovery in the FK506 and ADSC groups, but there was no difference between them. Recovery in function was also achieved in the SLN group, but it was inferior (P<.05). Electromyography demonstrated superior nerve regeneration in the FK506 and ADSC groups compared with the SLN group (P<.05), with no difference between the FK506 and ADSC groups. Similarly, histology showed no difference between the FK506 and ADSC groups, although both outperformed the SLN group (P<.05). No complications were observed. Successful peripheral nerve regeneration can be accomplished after a 10-mm nerve defect treated with nerve conduits. Superior nerve regeneration may be expected when the conduits are loaded with undifferentiated ADSCs or FK506, with similar outcomes for ADSCs and FK506. [Orthopedics. 2023;46(6):e353-e361.].

Electrical stimulation or tacrolimus (FK506) alone enhances nerve regeneration and recovery after nerve surgery, while dual use reduces variance and combines strengths of each in promoting enhanced outcomes

INTRODUCTION/AIMS

Repaired nerve injuries can fail to achieve functional recovery. Therapeutic options beyond surgery, such as systemic tacrolimus (FK506) and electrical stimulation (E-stim), can improve recovery. We tested whether dual administration of FK506 and E-stim enhances regeneration and recovery more than either therapeutic alone.

METHODS

Rats were randomized to four groups: E-stim, FK506, FK506 + E-stim, and repair alone. All groups underwent tibial nerve transection and repair. Two sets of animals were created to measure outcomes of early nerve regeneration using nerve histology (n = 36) and functional recovery (n = 42) (21- and 42-day endpoints, respectively). Functional recovery was measured by behavioral analyses (walking track and grid walk) and, at the endpoint, muscle mass and force.

RESULTS

Dual E-stim and FK506 administration produced histomorphometric measurements of nerve regeneration no different than either therapeutic alone. All treatments were superior to repair alone (FK506, P < .0001; E-stim, P < .05; FK506 + E-stim, P < .05). The E-stim and FK506 + E-stim groups had improved behavioral recovery compared with repair alone (at 6 weeks: E-stim, P < .05; FK506 + E-stim, P < .01). The FK506 group had improved recovery based on walking-track analysis (at 6 weeks: P < .001) and muscle force and mass (P < .05). The concurrent use of both therapies ensured earlier functional recovery and decreased variability in functional outcomes compared with either therapy alone, suggesting a moderate benefit.

DISCUSSION

Dual administration of FK506 and E-stim showed minimal additive effects to further improve regeneration or recovery compared with either therapy alone. The data suggest the combination of FK506 and E-stim appears to combine the relative strengths of each therapeutic.

Effect of Tacrolimus and Cyclosporine Immunosuppressants on Peripheral Nerve Regeneration: Systematic Review and Meta-analysis

Peripheral nerve damage is an important cause of seeking medical attention. It occurs when the continuity of structures is interrupted and the propagation of nervous impulses is blocked, affecting the functional capacity of individuals. To assess the effects of the immunosuppressants tacrolimus and cyclosporine on the regeneration of peripheral nerves, a systematic review of the literature was carried out. The articles included were published until September 2018 and proposed to evaluate the effects of the immunosuppressants tacrolimus and cyclosporine on nerve regeneration and neuroprotection, available in the MEDLINE, EMBASE, Cochrane Library, Web of Science, Oxford Pain Relief Database, and LILACS databases. The research analysed a total of 56 articles, of which 22 were included in the meta-analysis. Statistical analysis suggests the protective effect of tacrolimus in the regeneration of the number of myelinated axons (95% confidence interval [CI]: 0.93–2.39; p  < 0.01); however, such effect was not observed in relation to cyclosporine (95%CI: - 0.38–1.18; p  = 0.08) It also suggests that there is a significant relationship between the use of tacrolimus and myelin thickness (95%CI= 2.00–5.71; p  < 0. 01). The use of immunosuppressants in the regeneration of peripheral nerve damage promotes an increase in the number of myelinated axons in general, regardless of the administered dose. In addition, it ensures greater myelin thickness, muscle weight and recovery of the sciatic functional index. However, heterogeneity was high in most analyses performed.

The effect of FK506 (tacrolimus) loaded with collagen membrane and fibrin glue on promotion of nerve regeneration in a rat sciatic nerve traction injury model

Background

Peripheral nerve injury is one of the most common injuries that might occur in oral and maxillofacial surgery. The purpose of this study was to determine the effect of FK506 loaded with collagen membrane and fibrin glue on the promotion of nerve regeneration after traction nerve injury in a rat model.

Methods

Thirty male Sprague-Dawley rats were divided into three groups: group A (n = 10), a sham group whose sciatic nerve was exposed without any injury; and groups B (n = 10) and C (n = 10), which underwent traction nerve injury using 200 g of traction force for 1 min. The injured nerve in group C was covered with a collagen membrane soaked with FK506 (0.5 mg/0.1 mL) and fibrin glue. Functional analysis and microscopic evaluation were performed at 2 and 4 weeks after injury.

Results

The sciatic function index was − 5.78 ± 3.07 for group A, − 20.69 ± 5.22 for group B, and − 12.01 ± 4.20 for group C at 2 weeks after injury. However, at 4 weeks, the sciatic function index was − 5.58 ± 2.45 for group A, − 19.69 ± 4.81 for group B, and − 11.95 ± 1.94 for group C. In both periods, statistically significant differences were found among the groups (p<0.017). Histomorphometric evaluation revealed improved nerve regeneration in group C compared to that in group B. However, no statistical differences in axonal density were found among the three groups (p < 0.017).

Conclusion

Localized FK506 with collagen membrane and fibrin glue could promote axonal regeneration in a rat model of traction nerve injury.

Effect of acellular nerve scaffold containing human umbilical cord-derived mesenchymal stem cells on nerve repair and regeneration in rats with sciatic nerve defect

Background

The aim of the present study was to investigate the effect of acellular nerve scaffold (ANS) containing human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) on nerve repair and regeneration in rats with sciatic nerve defect.

Methods

Sciatic nerve trunks were removed from 6 female Sprague-Dawley (SD) rats, and ANS was prepared by lyophilization + enzymatic method and divided into A, B, C, D and E groups according to different treatment times. hUC-MSCs were isolated from the collected umbilical cords and cultured, and then ANS-hUC-MSCs complexes were made. The other 24 adult female SD rats were randomly divided into the control, autograft, ANS, and ANS-hUC-MSCs groups, and a rat model of sciatic nerve defect was established. Hematoxylin-eosin (HE) staining, Luxol fast blue (LFB) staining, Masson staining, and scanning electron microscopy were used to observe the morphology and tissue structure of ANS. The performance of ANS was evaluated by mechanical detection, and hydroxyproline (HYP) content was evaluated using a biochemical kit. Flow cytometry was adopted to detect the levels of hUC-MSCs surface antigens CD29, CD44, and CD34, as well as electrophysiological detection and muscle wet weight recovery rate for measuring rat muscle performance.

Results

ANS was prepared according to group A method and had good mechanical properties, with less residues of cells and myelin, and higher HYP content, indicating that this scaffold had the best performance. ANS-hUC-MSCs significantly reduced myelin injury in the sciatic nerve, and increased axonal regeneration, effectively improving sciatic nerve injury in rats. In addition, ANS-hUC-MSCs significantly increased compound muscle action potential (CMAP), nerve conduction velocity (NCV), and muscle wet weight, and reduced muscle atrophy.

Conclusions

ANS containing hUC-MSCs can promote nerve repair and regeneration in rats with sciatic nerve defects.

Advances in the repair of segmental nerve injuries and trends in reconstruction

Despite advances in surgery, the reconstruction of segmental nerve injuries continues to pose challenges. In this review, current neurobiology regarding regeneration across a nerve defect is discussed in detail. Recent findings include the complex roles of nonneuronal cells in nerve defect regeneration, such as the role of the innate immune system in angiogenesis and how Schwann cells migrate within the defect. Clinically, the repair of nerve defects is still best served by using nerve autografts with the exception of small, noncritical sensory nerve defects, which can be repaired using autograft alternatives, such as processed or acellular nerve allografts. Given current clinical limits for when alternatives can be used, advanced solutions to repair nerve defects demonstrated in animals are highlighted. These highlights include alternatives designed with novel topology and materials, delivery of drugs specifically known to accelerate axon growth, and greater attention to the role of the immune system.

Neuroregenerative effects of polyethylene glycol and FK-506 in a rat model of sciatic nerve injury

The recently introduced polyethylene glycol (PEG) treatment restores axonal continuity after nerve injury, leading to rapid recovery of nerve function. The impact of PEG therapy on neuroregeneration has not yet been compared with any intervention with an established proneuroregenerative potential. FK-506 is an immunosuppressive agent with documented proneuroregenerative potential in nerve injury models. The aim of this study was to compare the effects of PEG therapy and preinjury FK-506 administration in rats with sciatic nerve transection injury. Four groups of male Sprague Dawley rats (seven per group) underwent sciatic nerve transection with primary repair. Group A received placebo injections, group B placebo injections and PEG treatment, group C FK-506 injections, and group D both FK-506 injections and PEG treatment. Clinical outcomes were assessed by the skin prick test and Sciatic Functional Index (SFI). Regenerated nerves underwent histomorphometric analysis. The histomorphometric analysis demonstrated that compared with the controls, nerve specimens from all treated groups showed signs of enhanced neuroregeneration (higher mean axonal area) (p < 0.001). The histomorphometric parameters for group D (PEG + FK-506), mean axonal area (p < 0.001) and axonal count (p > 0.05), were significantly better than those in the other study groups. The Form factor was closest to its optimal values in group B (p < 0.0001). At the end of the study, mean skin prick test scores in all treated groups were significantly higher than those in controls (p > 0.05). During the first postoperative week, PEG-treated rats (groups B and D) presented with higher values of the SFI than animals from groups A and C, but the difference was not statistically significant. Combined therapy with PEG and FK-506 seems to produce better neuroregeneration outcomes than a simple suture-based repair complemented with either PEG or FK-506 treatment.

Comparing electrical stimulation and tacrolimus (FK506) to enhance treating nerve injuries

INTRODUCTION

Neuroenhancing therapies are desired because repair of nerve injuries can fail to achieve recovery. We compared two neuroenhancing therapies, electrical stimulation (ES) and systemic tacrolimus (FK506), for their capabilities to enhance regeneration in the context of a rat model.

METHODS

Rats were randomized to four groups: ES 0.5 mA, ES 2.0 mA, FK506, and repair alone. All groups underwent tibial nerve transection and repair, and outcomes were assessed by using twice per week walking track analysis, cold allodynia response, relative muscle mass, and nerve histology.

RESULTS

Electrical stimulation and FK506 groups demonstrated improved functional recovery and myelinated axon counts distal to the repair compared with repair alone. Electrical stimulation provided improvements in nerve regeneration that were not different from optimized FK506 systemic administration.

DISCUSSION

Providing ES after nerve repair improved regeneration and recovery in rats, with minimal differences in therapeutic efficacy to FK506, further demonstrating its clinical potential to improve management of nerve injuries.

Knockout of toll-like receptor impairs nerve regeneration after a crush injury

Background

Toll-like receptors (TLRs) are involved in the initiation of Schwann cell activation and subsequent recruitment of macrophages for clearance of degenerated myelin and neuronal debris after nerve injury. The present study was designed to investigate the regenerative outcome and expression of myelination-related factors in Tlr-knockout mice following a sciatic nerve crush injury.

Materials and methods

A standard sciatic nerve crush injury, induced by applying constant pressure to the nerve with a No. 5 jeweler's forceps for 30 s, was performed in C57BL/6, Tlr2^−/−, Tlr3^−/−, Tlr4^−/−, Tlr5^−/−, and Tlr7^−/− mice. Quantitative histomorphometric analysis of toluidine blue-stained nerve specimens and walking track analysis were performed to evaluate nerve regeneration outcomes. PCR Arrays were used to detect the expression of neurogenesis-related genes of dorsal root ganglia as well as of myelination-related genes of the distal nerve segments.

Results

Worse nerve regeneration after nerve crush injury was found in all Tlr-knockout mice than in C57BL/6 mice. Delayed expression of myelin genes and a different expression pattern of myelination-related neurotrophin genes and transcription factors were found in Tlr-knockout mice in comparison to C57BL/6 mice. In these TLR-mediated pathways, insulin-like growth factor 2 and brain-derived neurotrophic factor, as well as early growth response 2 and N-myc downstream-regulated gene 1, were significantly decreased in the early and late stages, respectively, of nerve regeneration after a crush injury.

Conclusions

Knockout of Tlr genes decreases the expression of myelination-related factors and impairs nerve regeneration after a sciatic nerve crush injury.

Human periodontal ligament stem cells repair mental nerve injury

Human periodontal ligament stem cells are easily accessible and can differentiate into Schwann cells. We hypothesized that human periodontal ligament stem cells can be used as an alternative source for the autologous Schwann cells in promoting the regeneration of injured peripheral nerve. To validate this hypothesis, human periodontal ligament stem cells (1 × 10⁶) were injected into the crush-injured left mental nerve in rats. Simultaneously, autologous Schwann cells (1 × 10⁶) and PBS were also injected as controls. Real-time reverse transcriptase polymerase chain reaction showed that at 5 days after injection, mRNA expression of low affinity nerve growth factor receptor was significantaly increased in the left trigeminal ganglion of rats with mental nerve injury. Sensory tests, histomorphometric evaluation and retrograde labeling demonstrated that at 2 and 4 weeks after injection, sensory function was significantly improved, the numbers of retrograde labeled sensory neurons and myelinated axons were significantly increased, and human periodontal ligament stem cells and autologous Schwann cells exhibited similar therapeutic effects. These findings suggest that transplantation of human periodontal ligament stem cells show a potential value in repair of mental nerve injury.

Knockout of TLR4 and TLR2 impair the nerve regeneration by delayed demyelination but not remyelination

Background

Knockout of either toll-like receptor 4 (TLR4) or 2 (TLR2) had been reported to delay the Wallerian degeneration after peripheral nerve injury by deterring the recruitment of the macrophages and clearance of myelin debris. However, the impact on the remyelination process is poorly understood. In this study, the effect of TLR2 and TLR4 knockout on the nerve regeneration and on the remyelination process was studied in a mouse model of sciatic nerve crush injury.

Results

A standard sciatic nerve crush injury by a No. 5 Jeweler forcep for consistent 30 seconds was performed in Tlr4^−/− (B6.B10ScN-Tlr4^lps-del/JthJ), Tlr2^−/− (B6.129-Tlr2^tm1Kir/J) and C57BL/6 mice. One centimeter of nerve segment distal to the crushed site was harvested for western blot analysis of the myelin structure protein myelin protein zero (Mpz) and the remyelination transcription factors Oct6 and Sox10 at day 0, 3, 7, 10, 14, 17, 21, 28. Nerve segment 5-mm distal to injured site from additional groups of mice at day 10 after crush injury were subjected to semi-thin section and toluidine blue stain for a quantitative histomorphometric analysis. With less remyelinated nerves and more nerve debris, the histomorphometric analysis revealed a worse nerve regeneration following the sciatic nerve crush injury in both Tlr4^−/− and Tlr2^−/− mice than the C57BL/6 mice. Although there was a delayed expression of Sox10 but not Oct6 during remyelination, with an average 4-day delay in the demyelination process, the subsequent complete formation of Mpz during remyelination was also delayed for 4 days, implying that the impaired nerve regeneration was mainly attributed to the delayed demyelination process.

Conclusions

Both TLR4 and TLR2 are crucial for nerve regeneration after nerve crush injury mainly by delaying the demyelination but not the remyelination process.

Tolerance and effects of FK506 (tacrolimus) on nerve regeneration: a pilot study

In adults, the outcome of nerve suture and nerve autograft remains generally unsatisfactory. FK506 (tacrolimus), an immunosuppressant drug used in transplantation, has been reported in animal studies to enhance nerve regeneration. In hand transplantation patients, nerve regeneration was unexpectedly good and rapid, and this observation has been attributed to FK506. The present Phase II experiment investigated the tolerance to FK506 after nerve suture or autograft, and the potential effects of the drug on axonal regeneration. Following strict criteria, five patients were included in this study. Within 7 days of nerve repair (median, ulnar and sciatic transections), patients received FK506 (aiming for blood concentrations between 5 and 8 ng/ml) for a total duration of 60 days. The patients were carefully followed with clinical and biological monitoring in order to detect side-effects. A clinical and electrophysiological assessment of the effect of FK506 on nerve regeneration was conducted. No undesirable side-effect was observed during or after FK506 treatment, but one non-compliant patient discontinued treatment. There was no evident improvement of sensory, motor or functional recovery at the end of the follow-up period (average duration 39.8 months), as compared to the expected clinical result without treatment. Although statistically non-significant, FK506 seemed to accelerate the progression of the Hoffmann-Tinel sign, but without impact on the final result.

Immunological demyelination enhances nerve regeneration after acute transection injury in the adult rat sciatic nerve

INTRODUCTION

Our recent experiments demonstrate that demyelination enhances peripheral nerve regeneration after contusion injury in the adult rat sciatic nerve. The role of demyelination in peripheral nerve regeneration in a sciatic nerve transection model has yet to be elucidated. We hypothesize that (1) axon regeneration within a region of injury increases after experimental, immunologic demyelination, and (2) regenerated axons are partially derived from the proximal motor axons.

METHODS

Sciatic nerves of adult female Sprague-Dawley rats (n = 20) were injected with a demyelinating agent immediately after transection injury. The sciatic nerves were harvested 1 month (n = 5) and 2 months (n = 5) after surgery. In the control groups, the cut nerves were reapproximated without demyelination therapy. The lesion containing length of nerve was cut into 1-mm transverse blocks and processed to preserve orientation. Specimens were evaluated using structural and immunohistochemical analyses.

RESULTS

A single epineural injection of complement proteins plus antibodies to galactocerebroside resulted in demyelination followed by Schwann cell remyelination. At 1 month, remyelination was clearly shown throughout the injured sciatic nerve segment. At 2 months, there was a statistically significant increase in peripheral nerve regeneration following demyelination therapy as evidenced by total axon count, axon density, and fiber diameter.

CONCLUSION

This study demonstrates enhanced histomorphologic nerve regeneration in the rat sciatic nerve after local delivery of experimental, immunologic demyelination following transection injury. It highlights the utility of demyelination in peripheral nerve regeneration. This therapy may be applicable for tissue-engineered constructs, cell-based systems, and nerve transfers to improve outcomes in peripheral nervous system injuries.

The role of immunophilin ligands in nerve regeneration

Tacrolimus (FK506) is a widely used immunosuppressant in organ transplantation. However, it also has neurotrophic activity that occurs independently of its immunosuppressive effects. Other neurotrophic immunophilin ligands that do not exhibit immunosuppression have subsequently been developed and studied in various models of nerve injury. This article reviews the literature on the use of tacrolimus and other immunophilin ligands in peripheral nerve, cranial nerve and spinal cord injuries. The most convincing evidence of enhanced nerve regeneration is seen with systemic administration of tacrolimus in peripheral nerve injury, although clinical use is limited due to its immunosuppressive side effects. Local tacrolimus delivery to the site of nerve repair in peripheral and cranial nerve injury is less effective but requires further investigation. Tacrolimus can enhance outcomes in nerve allograft reconstruction and accelerates reinnervation of complex functional allograft transplants. Other non-immunosuppressive immunophilins ligands such as V-10367 and FK1706 demonstrate enhanced neuroregeneration in the peripheral nervous system and CNS. Mixed results are found in the application of immunophilin ligands to treat spinal cord injury. Immunophilin ligands have great potential in the treatment of nerve injury, but further preclinical studies are necessary to permit translation into clinical trials.

Efficacy of Short-Term FK506 Administration on Accelerating Nerve Regeneration

Background. The slow rate of nerve regeneration following injury can cause extended muscle denervation, leading to irreversible muscle atrophy, fibrosis, and destruction of motor endplates. The immunosuppressant FK506 (tacrolimus) has been shown to accelerate the rate of nerve regeneration and functional recovery. However, the toxic and immunosuppressive properties of FK506 make it undesirable for long-term use. Objective. To take advantage of the regeneration-enhancing effects of FK506 but avoid the potential adverse effects of long-term administration, the current study evaluates and quantifies the efficacy of short-term FK506 treatment in rat models. Methods. Clinically relevant transection and graft models were evaluated, and walking track analysis (WTA) was used to evaluate functional recovery. FK506 was administered for 5 and 10 days post transection injury and 10 and 20 days post graft injury. Both groups involving a short course were compared with the continuous administration group. Results. In the transection model, FK506 was administered for 5 and 10 days postoperatively. WTA demonstrated that 10 days of FK506 administration was sufficient to reduce functional recovery time by 29% compared with negative controls. In the graft model, FK506 was administered for 10 and 20 days postoperatively. Short treatment courses of 10 and 20 days reduced recovery time by 15% and 21%, respectively, compared with negative controls. Analysis of blood–nerve barrier (BNB) integrity demonstrated that FK506 facilitated early reconstitution of the BNB. Conclusions. The results of this study indicate that short-term FK506 delivery following nerve injury imparts a significant therapeutic effect.

Clinical strategies to enhance nerve regeneration in composite tissue allotransplantation

Reinnervation of a hand transplant ultimately dictates functional recovery but provides a significant regenerative challenge. This article highlights interventions to enhance nerve regeneration through acceleration of axonal regeneration or augmentation of Schwann cell support and discuss their relevance to composite tissue allotransplantation. Surgical techniques that may be performed at the time of transplantation to optimize intrinsic muscle recovery--including appropriate alignment of ulnar nerve motor and sensory components, transfer of the distal anterior interosseous nerve to the recurrent motor branch of the median nerve, and prophylactic release of potential nerve entrapment points--are also presented.

A novel model for evaluating nerve regeneration in the composite tissue transplant: the murine heterotopic limb transplant

PURPOSE

For individuals who have experienced debilitating upper extremity injury or amputation, hand transplantation holds the potential for drastic quality of life improvement. This potential depends on adequate nerve regeneration into the transplant and reanimation of graft musculature. In this study, we demonstrate the use of a murine heterotopic limb transplant model for evaluation of nerve regeneration in a composite tissue allograft (CTA). We also compare the effects of various immunosuppressive regimens on nerve regeneration in this model.

METHODS

The study consisted of five groups of mice, all of which underwent heterotopic limb transplant with coaptation of the recipient and donor sciatic nerves. The groups received the following immunosuppressive regimens: group A (positive control)-syngeneic transplant, no immunosuppression; group B (negative control)-allogeneic transplant, no immunosuppression; group C-allogeneic transplant, FK-506 + MR1; group D-allogeneic transplant, MR1 + CTLA4-Ig; group E-syngeneic transplant, FK-506 treatment with preloading.

RESULTS

Group B animals showed signs of transplant rejection as early as 5 days postoperatively. Except for one mouse from group C and one mouse from group D, all other animals had viable transplants and nerve regeneration present in the donor sciatic nerve at the 3-week endpoint of the study.

CONCLUSIONS

To our knowledge, this represents the first report of the use of a mouse CTA model for evaluation of nerve regeneration. The mouse heterotopic limb transplant model will be a valuable tool for CTA research since it can be performed with more ease, and with less host morbidity and mortality than the mouse orthotopic model.

Evaluation of peripheral nerve regeneration via in vivo serial transcutaneous imaging using transgenic Thy1-YFP mice

This study uses the saphenous nerve crush model in Thy1-YFP mice and serial transcutaneous imaging to evaluate the rate of nerve regeneration under various FK-506 (tacrolimus) dosing regimens and in the presence of transgenic overexpression of glial cell line-derived neurotrophic factor (GDNF). Thy1-YFP transgenic mice received saphenous nerve crush and were monitored for axonal regeneration via transcutaneous imaging for 7 days. Group A received no FK-506. Groups B and C received FK-506 at 2 or 0.5 mg/kg/day, starting three days before injury (preload). Groups D and E received FK-506 at 2 or 0.5 mg/kg/day, starting on the day of injury. Group F consisted of double transgenic mice with central overexpression of GDNF by CNS astrocytes (GFAP-GDNF/Thy1-YFP). Length and rate of axonal regeneration were measured and calculated over time. Regardless of concentration, FK-506 preload (Groups B and C) improved length and rate of axonal outgrowth compared with controls (Group A) and no preload (Groups D and E). Surprisingly, central overexpression of GDNF (GFAP-GDNF) delayed and stunted axonal outgrowth. Saphenous nerve crush in Thy1-YFP mice represents a viable model for timely evaluation of therapeutic strategies affecting the rate of nerve regeneration. FK-506 administered three days prior to injury accelerates axonal regeneration beyond injury conditioned regeneration alone and may serve as a reliable positive control for the model. GDNF overexpression in the CNS impedes early axonal outgrowth.

Peptide therapy with pentadecapeptide BPC 157 in traumatic nerve injury

We focused on the healing of rat transected sciatic nerve and improvement made by stable gastric pentadecapeptide BPC 157 (10 microg, 10ng/kg) applied shortly after injury (i) intraperitoneally/intragastrically/locally, at the site of anastomosis, or after (ii) non-anastomozed nerve tubing (7 mm nerve segment resected) directly into the tube. Improvement was shown clinically (autotomy), microscopically/morphometrically and functionally (EMG, one or two months post-injury, walking recovery (sciatic functional index (SFI)) at weekly intervals). BPC 157-rats exhibited faster axonal regeneration: histomorphometrically (improved presentation of neural fascicles, homogeneous regeneration pattern, increased density and size of regenerative fibers, existence of epineural and perineural regeneration, uniform target orientation of regenerative fibers, and higher proportion of neural vs. connective tissue, all fascicles in each nerve showed increased diameter of myelinated fibers, thickness of myelin sheet, number of myelinated fibers per area and myelinated fibers as a percentage of the nerve transected area and the increased blood vessels presentation), electrophysiologically (increased motor action potentials), functionally (improved SFI), the autotomy absent. Thus, BPC 157 markedly improved rat sciatic nerve healing.

Nerve allotransplantation as it pertains to composite tissue transplantation

Nerve allografts provide a temporary scaffold for host nerve regeneration and allow for the repair of significant segmental nerve injuries. From rodent, large animal, and nonhuman primate studies, as well as clinical experience, nerve allografts, with the use of immunosuppression, have the capacity to provide equal regeneration and function to that of an autograft. In contrast to solid organ transplantation and composite tissue transfers, nerve allograft transplantation requires only temporary immunosuppression. Furthermore, nerve allograft rejection is difficult to assess, as the nerves are surgically buried and are without an immediate functional endpoint to monitor. In this article, we review what we know about peripheral nerve allograft transplantation from three decades of experience and apply our current understanding of nerve regeneration to the emerging field of composite tissue transplantation.