FK506 promotes functional recovery in crushed rat sciatic nerve

A World Update of Progress in Lower Extremity Transplantation: What's Hot and What's Not

ABSTRACT

The field of vascularized composite allotransplantation (VCA) is the new frontier of solid organ transplantation (SOT). VCA spans life-enhancing/life-changing procedures such as upper extremity, craniofacial (including eye), laryngeal, tracheal, abdominal wall, penis, and lower extremity transplants. VCAs such as uterus transplants are life giving unlike any other SOT. Of all VCAs that have shown successful intermediate- to long-term graft survival with functional and immunologic outcomes, lower extremity VCAs have remained largely underexplored. Lower extremity transplantation (LET) can offer patients with improved function compared to the use of conventional prostheses, reducing concerns of phantom limb pain and stump complications, and offer an option for eligible amputees that either fail prosthetic rehabilitation or do not adapt to prosthetics. Nevertheless, these benefits must be carefully weighed against the risks of VCA, which are not trivial, including the adverse effects of lifelong immunosuppression, extremely challenging perioperative care, and delayed nerve regeneration. There have been 5 lower extremity transplants to date, ranging from unilateral or bilateral to quadrimembral, progressively increasing in risk that resulted in fatalities in 3 of the 5 cases, emphasizing the inherent risks. The advantages of LET over prosthetics must be carefully weighed, demanding rigorous candidate selection for optimal outcomes.

Local delivery of FK506 to a nerve allograft is comparable to systemic delivery at suppressing allogeneic graft rejection

The objective of this study was to determine if locally delivered FK506 could prevent allogeneic nerve graft rejection long enough to allow axon regeneration to pass through the nerve graft. An 8mm mouse sciatic nerve gap injury repaired with a nerve allograft was used to assess the effectiveness of local FK506 immunosuppressive therapy. FK506-loaded poly(lactide-co-caprolactone) nerve conduits were used to provide sustained local FK506 delivery to nerve allografts. Continuous and temporary systemic FK506 therapy to nerve allografts, and autograft repair were used as control groups. Serial assessment of inflammatory cell and CD4+ cell infiltration into the nerve graft tissue was performed to characterize the immune response over time. Nerve regeneration and functional recovery was serially assessed by nerve histomorphometry, gastrocnemius muscle mass recovery, and the ladder rung skilled locomotion assay. At the end of the study, week 16, all the groups had similar levels of inflammatory cell infiltration. The local FK506 and continuous systemic FK506 groups had similar levels of CD4+ cell infiltration, however, it was significantly greater than the autograft control. In terms of nerve histmorphometry, the local FK506 and continunous systemic FK506 groups had similar amounts of myelinated axons, although they were significantly lower than the autograft and temporary systemic FK506 group. The autograft had significantly greater muscle mass recovery than all the other groups. In the ladder rung assay, the autograft, local FK506, and continuous systemic FK506 had similar levels of skilled locomotion performance, whereas the temporary systemic FK506 group had significanty better performance than all the other groups. The results of this study suggest that local delivery of FK506 can provide comparable immunosuppression and nerve regeneration outcomes as systemically delivered FK506.

Efficacy of platelet-rich fibrin and tacrolimus on facial nerve regeneration: an animal study

This study was performed to investigate the effect of platelet-rich fibrin membrane (PRFM), alone and with topical tacrolimus application, on regeneration of the crushed facial nerve (FN). Thirty healthy 7-week-old albino rats were used. The left FN was damaged by crushing in all rats. Three random groups of rats were formed: group 1, untreated; group 2, treated with PRFM; group 3, treated with PRFM plus topical tacrolimus. Functional recovery and histological and immunohistochemical evaluations were performed 4 and 8 weeks later. Anti-S100 was used to detect myelin sheath. At 4 weeks, blinking reflex recovery was more rapid in group 3 than in groups 2 and 1 (4.30 ± 0.48, 3.40 ± 0.52, and 2.20 ± 0.42, respectively); the difference was statistically significant (P = 0.001). Histologically, group 3 showed more apparent normal FN structures than the other groups. Immunohistochemical caspase-3 evaluation of the axon area revealed a significant difference between group 2 (PRFM alone; 8.67 ± 0.029) and group 3 (PRFM plus topical tacrolimus; 4.42 ± 0.028) (P = 0.001). Group 3 showed the greatest positive staining in the myelin sheath. Based on the results of this animal study, clinical studies should be performed to determine whether the combination of PRF and tacrolimus also improves the outcome of nerve regeneration in humans.

Effect of Tacrolimus on Peripheral Nerve Regeneration in Allograft Transplantation: A Light and Electron Microscopic Study

OBJECTIVES

Peripheral nerve injuries are common in Europe; however, the treatment techniques may lead to disabilities. This study aimed to evaluate the effect of tacrolimus use on the capacity of the epineural sheath graft to improve its regeneration quality in rat sciatic nerves as a treatment option for nerve injuries.

MATERIALS AND METHODS

In the experimental process, 30 male Sprague Dawley were used as recipients and 10 Wistar rats were used as donors. Under anesthesia, all rats were operated on to resect the sciatic nerve. The nerve tissue of Wistar rats was used as allograft. In the autograft group, the resected nerve was reversed and sutured, resulting in an epineural sheath graft. For the allograft groups, rats were randomly divided into 2 groups as the tacrolimus-treated group and the nontreated group after allograft transplant. Tacrolimus was administered intramuscularly at 0.1 mg/kg daily for 12 weeks. After the treatment period, rats were killed and evaluated histomorphologically with light and electron microscopy.

RESULTS

Histological examination showed no remarkable differences between different regions of the sciatic nerves (distal, middle, and proximal). The axonal density was decreased in the allograft groups compared with the autograft group (P < .001). Results showed that the number of mast cells was increased in the allograft group without tacrolimus treatment (P < .05). Similarly, there was a mild increase in mast cell count in the tacrolimus-treated allograft group.

CONCLUSIONS

Our results showed that tacrolimus use in rats with implanted epineural nerve sheath supported recovery in terms of morphological and physiological regeneration of the nerve.

Role of tacrolimus in return of hand function after brachial plexus injury in a lung transplantation patient

We report a patient who has been on tacrolimus for bilateral lung transplantation and presented with a brachial plexus injury (BPI), with unusual improvement of lower trunk innervated hand function. The lower trunk injury with resultant left hand paralysis had developed after his sternotomy 18 months ago. He has been treated with tacrolimus as part of his immunosuppression protocol since the surgery, without severe side effects. Physical examination at 18 months demonstrated unusual excellent grip pattern and full opposition of his thumb with slight claw deformity of his ulnar two digits. While the neurotoxic effects of tacrolimus are more emphasised, the neuroregenerative properties have been recently explored. The recovery in this patient is unique and unusual after BPI and is most likely as a result of the low dose tacrolimus treatment.

The therapeutic efficacy of dexpanthenol on sciatic nerve injury in a rat model

Objective: The aim of this study was to evaluate histopathological, functional and bone densitometry examinations of the beneficial effects of dexpanthenol (DEX) on nerve regeneration in a rat model of peripheral nerve crush injury.Methods: Thirty adult Sprague-Dawley rats were divided equally into three groups. A crush injury was simulated in all rats by clamping the right sciatic nerve for one minute. In group 1, one day before the surgical procedure, 500 mg/kg DEX administered via intraperitoneally (ip) was initiated and continued three times in a week during the experiment period as 28 days. In group 2, rats received a dose of 10 mg/kg DEX to investigate possible effects of DEX alone. Group 3 served as the control (sciatic nerve injury) and was not given any drugs.Results: Performance was significantly lower in group 3 compared to the drug treatment groups during the rotarod test (30 rpm and 40 rpm) (p < 0.05). After a while, the rats which were able to remain on the rod was significantly lower in group 3 during the acceleration test (p < 0.05). Hot plate latency test results in group 3 were significantly lower when compared to the other groups (p < 0.05).Conclusion: DEX appears to be useful as a supportive clinical agent for the treatment of pain and nerve damage.

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.

Local FK506 delivery at the direct nerve repair site improves nerve regeneration

INTRODUCTION

The objective of this study is to assess the efficacy of local tacrolimus (FK506) delivery to improve outcomes in the setting of nerve transection injury.

METHODS

FK506 embedded poly(lactide-co-caprolactone) films capable of extended, localized release of FK506 were developed. FK506 rate of release testing and bioactivity assay was performed. Mouse sciatic nerve transection and direct repair model was used to evaluate the effect extended, local delivery of FK506 had on nerve regeneration outcomes.

RESULTS

Linear release of FK506 was observed for 30 days and released FK506 matched control levels of neurite extension in the dorsal root ganglion assay. Groups treated with local FK506 had greater gastrocnemius muscle weight, foot electromyogram, and number of axons distal of the repair site than non-FK506 groups.

DISCUSSION

Results of this study indicate that extended, localized delivery of FK506 to nerve injuries can improve nerve regeneration outcomes in a mouse sciatic nerve transection and repair.

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.

A morphological and biochemical evaluation of the effects of quercetin on experimental sciatic nerve damage in rats

The present study evaluated the neuroprotective and antioxidant effects of quercetin in a rat model of sciatic nerve crush injury using histopathological, morphometric and biochemical methods. A total of 48 male Sprague Dawley rats, aged 10-12 weeks old were randomly divided into eight groups, consisting of two sham groups (S-7, S-28), three quercetin-treated groups (Q-7, Q-28; 200 mg/kg/7 days), trauma (T-7, T-28; 1 min sciatic nerve crush injury) and three trauma+quercetin groups (T+Q-7, T+Q-28; trauma+quercetin 200 mg/kg/7 days). Rats were sacrificed on day 7 or 28. Oxidant-antioxidant biochemical parameters in nerve tissues from all groups were analyzed using histopathological staining with toluidine blue and Masson's trichrome. DNA fragmentations were identified using terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling in cells from each tissue sample. Degeneration of the axons and myelin sheath, the breakdown of the concentric lamellar structure of the myelin sheath and axonal swelling were observed in groups T-7 and T-28. Myelin sheath thicknesses, nerve fiber diameters and the number of myelinated nerve fibers decreased, while the apoptotic index (AI) increased in the T-7 and T-28 groups. However, it was observed that nerve regeneration began in the T+Q-7 and T+Q-28 groups compared with the sham groups, together with the healing of cellular damage and axonal structure and a decrease in the AI. Malondialdehyde and superoxide dismutase activity did not differ significantly between the T-7 and S-7 groups. However, catalase activity significantly decreased in the T-28 group when compared with the sham 7 day group. Tissue malondialdehyde levels significantly increased, while serum catalase activity increased in the T+Q-7 group compared with the T-7 group. These results suggest that quercetin has beneficial effects on nerve regeneration and may shorten the healing period in crush-type sciatic nerve injuries.

Controlled release of FK506 from micropatterned PLGA films: potential for application in peripheral nerve repair

After decades of research, peripheral nerve injury and repair still frequently results in paralysis, chronic pain and neuropathies leading to severe disability in patients. Current clinically available nerve conduits only provide crude guidance of regenerating axons across nerve gap without additional functionality. FK506 (Tacrolimus), an FDA approved immunosuppressant, has been shown to enhance peripheral nerve regeneration but carries harsh side-effects when delivered systemically. The objective of this study was to develop and evaluate a bioresorbable drug delivery system capable of local extended delivery of FK506 that also provides topological guidance cues to guide axon growth via microgrooves. Photolithography was used to create micropatterned poly(lactide-co-glycolic acid) (PLGA) films embedded with FK506. Non-patterned, 10/10 μm (ridge/groove width), and 30/30 μm patterned films loaded with 0, 1, and 3 μg/cm² FK506 were manufactured and characterized. In vitro FK506 rate of release testing indicated that the films are capable of an extended (at least 56 days), controlled, and scalable release of FK506. Neurite extension bioactivity assay indicated that FK506 released from the films (concentration of samples tested ranged between 8.46–19.7 ng/mL) maintained its neural bioactivity and promoted neurite extension similar to control FK506 dosages (10 ng/mL FK506). The multi-functional FK506 embedded, micropatterned poly(lactide-co-glycolic acid) films developed in this study have potential to be used in the construction of peripheral nerve repair devices.

The effect of full dose composite tissue allotransplantation immunosuppression on allograft motor nerve regeneration in a rat sciatic nerve model

BACKGROUND

The purpose of this study was to identify which triple immunosuppressive protocols, currently used for vascularized composite allotransplantation in the clinic, will have the best effect on motor function recovery following nerve allograft reconstruction.

METHODS

Eighty-eight Lewis rats underwent a 1-cm sciatic nerve allograft transplantation and skin graft from 44 Brown-Norway rats. Group I received 0.9% isotonic saline (control); Group II, 2 mg/kg FK506; Group III, 1 mg/kg FK506 with 15 mg/kg mycophenolate mofetil (MMF); and Group IV, 2 mg/kg FK506 with 30 mg/kg MMF and prednisone. Each group consisted of 11 rats. After 12 weeks, motor function recovery was evaluated with isometric tetanic force, muscle mass, ankle contracture angle, electrophysiology, and nerve histomorphometry. Adequacy of immunosuppression was monitored with the transplanted skin graft. All data are expressed as a percentage of the contralateral side.

RESULTS

Isometric tetanic force showed significantly better functional recovery in all groups treated with immunosuppression compared to control. Within the immunosuppression groups no significant difference was found: 42.1 ± 6.4% (Group I), 56.1 ± 12.4% (Group II), 58.4 ± 10.7% (Group III), and 61.3 ± 11.2% (Group IV). Group IV was superior to all other groups regarding ankle contracture (P < .05) and electrophysiology (P < .001). Skin graft rejection occurred in 41 and 0% (Groups III and IV, respectively).

CONCLUSIONS

FK506 significantly enhanced motor recovery after allograft reconstruction. This effect was comparable between combination treatment (low-dose FK506 and MMF) and triple therapy (high-dose FK506 and MMF plus prednisolone). However, triple therapy was more effective in suppressing skin rejection.

Effect Of combining FK506 and neurotrophins on neurite branching and elongation

INTRODUCTION

There is a clinical need to improve the outcomes of peripheral nerve regeneration and repair after injury. In addition to its immunosuppressive effects, FK506 (tacrolimus) has been shown to have neuroregenerative properties. To determine biologically relevant local FK506 and growth factor concentrations, we performed an in vitro bioassay using dorsal root ganglion (DRG) from chicken embryos.

METHODS

Neurite elongation and neurite branching were analyzed microscopically after addition of FK506, glial cell line-derived neurotrophic factor (GDNF), and nerve growth factor (NGF), each alone and in combination.

RESULTS

FK506 induced modest neurite elongation (∼500-800 µm) without improving neurite branching significantly. The combination of FK506 with NGF, GDNF, or both, exerted a potentiating or competitive effect on neurite elongation (∼700-1100 µm) based on dosage and competitive effect on neurite branching (∼0.2-0.4).

CONCLUSIONS

These results strongly suggest that the interaction of FK506 with GDNF and NGF mediates distinct enhancement of neurite growth. Muscle Nerve 55: 570-581, 2017.

The effect of tacrolimus on facial nerve injury: Histopathological findings in a rabbit model

HYPOTHESIS

Tacrolimus helps healing of facial nerve injury.

BACKGROUND

Positive effects of tacrolimus on axon regeneration and healing of injured peripheral nerves (eg. sciatic nerve) have been reported in the literature. Tacrolimus may be an additional treatment method that could improve the nerve healing after surgical treatment of cut injury of facial nerve.

METHODS

20 New Zealand rabbits were randomly separated into control and study groups of 10. In control group, no medical treatment was given after facial nerve anastomosis, and the animals were followed up for 2months. In the study group rabbits were given 1mg/kg/day tacrolimus subcutaneously for 2months after the facial nerve anastomosis. The histopathologic findings of axon regeneration like axon myelination were analyzed in both groups under electron and light microscopy. The data obtained in the groups were compared.

RESULTS

Greater axon diameters, thicker myelin sheaths, and higher total number of myelinated axons were found in the tacrolimus group, suggesting better regeneration in this group when compared to the control group. There was less vacuolar degeneration in the study group. All these findings suggest that tacrolimus positively affects healing after facial nerve anastomosis.

CONCLUSION

The results of this study indicate that tacrolimus has favorable effects on the healing process of the facial nerve after end-to-end anastomosis. Tacrolimus may be a promising agent in the future for nerve regeneration following traumatic facial paralysis surgery.

Assessing the itching intensity using visual analogue scales in atopic dermatitis patients against the background of a therapy with calcineurin inhibitors

Goal. To assess the effect of topical treatment of atopic dermatitis patients with the 0.1% tacrolimus ointment on the itching intensity and skin expression level of growth factor proteins affecting the intensity of cutaneous innervation. Materials and methods. Fifteen patients suffering from atopic dermatitis underwent treatment with the 0.1% tacrolimus ointment. The SCORAD index was calculated to assess the severity of clinical manifestations. The itching intensity was assessed using a visual analogue scale. The skin expression of nerve growth factors, amphiregulin, semaphorin 3A and PGP9.5 protein (a nerve fiber marker) was assessed by the indirect immunofluorescence method. Results. An increased expression of the nerve growth factor and reduced semaphorin 3A expression levels were noted in the patients’ epidermis; there was an increase in the quantity, mean length and fluorescence intensity of PGP9.5+ nerve fibers. As a result of the treatment, the disease severity and itching intensity were reduced, the nerve growth factor expression level was reduced while semaphorin 3A expression level increased in the epidermis, and the mean length and fluorescence intensity of PGP9.5+ nerve fibers was also reduced. A positive correlation among the itching intensity and nerve growth factor expression level, quantity and mean length of PGP9.5+ nerve fibers in the epidermis was revealed, and negative correlation between the itching intensity and semaphorin 3A expression level in the epidermis was established. Conclusion. Topical treatment with the 0.1% Tacrolimus ointment reduces the itching intensity in atopic dermatitis patients, which is related to the therapy-mediated reduction in the epidermis innervation level, decreased expression of epidermal nerve growth factor and increased semaphorin 3A expression level.

The Effects of Phrenic Nerve Degeneration by Axotomy and Crush on the Electrical Activities of Diaphragm Muscles of Rats

The aim of this study was to investigate the effect of axotomy and crush-related degeneration on the electrical activities of diaphragm muscle strips of experimental rats. In the present study, twenty-one male Wistar-albino rats were used and divided into three groups. The animals in the first group were not crushed or axotomized and served as controls. Phrenic nerves of the rats in the second and third groups were crushed or axotomized in the diaphragm muscle. Resting membrane potential (RMP) was decreased significantly in both crush and axotomy of diaphragm muscle strips of experimental rats (p < 0.05). Depolarization time (T DEP) and half-repolarization (1/2 RT) time were significantly prolonged in crush and axotomy rats (p < 0.05). Crushing or axotomizing the phrenic nerves may produce electrical activities in the diaphragm muscle of the rat by depolarization time and half-repolarization time prolonged in crush and axotomy rats.

The Effect of Sildenafil on Recuperation from Sciatic Nerve Injury in Rats

BACKGROUND

Severe functional and anatomical defects can be detected after the peripheral nerve injury. Pharmacological approaches are preferred rather than surgical treatment in the treatment of nerve injuries.

AIMS

The aim of this study is to perform histopathological, functional and bone densitometry examinations of the effects of sildenafil on nerve regeneration in a rat model of peripheral nerve crush injury.

STUDY DESIGN

Animal experiment.

METHODS

The study included a total of thirty adult Sprague-Dawley rats that were divided into three groups of ten rats each. In all rats, a crush injury was created by clamping the right sciatic nerve for one minute. One day before the procedure, rats in group 1 were started on a 28-day treatment consisting of a daily dose of 20 mg/kg body weight sildenafil citrate given orally via a nasogastric tube, while the rats in group 2 were started on an every-other-day dose of 10 mg/kg body weight sildenafil citrate. Rats from group 3 were not administered any drugs. Forty-two days after the nerve damage was created, functional and histopathological examination of both sciatic nerves and bone densitometric evaluation of the extremities were conducted.

RESULTS

During the rotarod test, rats from group 3 spent the least amount of time on the rod compared to the drug treatment groups at speeds of 20 rpm, 30 rpm and 40 rpm. In addition, the duration for which each animal could stay on the rod throughout the accelerod test significantly reduced in rats from group 3 compared to rats from groups 1 and 2 in the 4-min test. For the hot-plate latency time, there were no differences among the groups in either the basal level or after sciatic nerve injury. Moreover, there was no significant difference between the groups in terms of the static sciatic index (SSI) on the 42(nd) day (p=0.147). The amplitude was better evaluated in group 1 compared to the other two groups (p<0.05). Under microscopic evaluation, we observed the greatest amount of nerve regeneration in group 1 and the lowest in group 3. However, this difference was not statistically significant. Moreover, there was no significant difference in the bone mineral density (BMD) levels among the groups.

CONCLUSION

We believe that a daily single dose of sildenafil plays an important role in the treatment of sciatic nerve damage and bone healing and thus can be used as supportive clinical treatment.

Canadian Association of Neuroscience Review: Axonal Regeneration in the Peripheral and Central Nervous Systems – Current Issues and Advances

Injured nerves regenerate their axons in the peripheral (PNS) but not the central nervous system (CNS). The contrasting capacities have been attributed to the growth permissive Schwann cells in the PNS and the growth inhibitory environment of the oligodendrocytes in the CNS. In the current review, we first contrast the robust regenerative response of injured PNS neurons with the weak response of the CNS neurons, and the capacity of Schwann cells and not the oligodendrocytes to support axonal regeneration. We then consider the factors that limit axonal regeneration in both the PNS and CNS. Limiting factors in the PNS include slow regeneration of axons across the injury site, progressive decline in the regenerative capacity of axotomized neurons (chronic axotomy) and progressive failure of denervated Schwann cells to support axonal regeneration (chronic denervation). In the CNS on the other hand, it is the poor regenerative response of neurons, the inhibitory proteins that are expressed by oligodendrocytes and act via a common receptor on CNS neurons, and the formation of the glial scar that prevent axonal regeneration in the CNS. Strategies to overcome these limitations in the PNS are considered in detail and contrasted with strategies in the CNS.

Does glioblastoma cyst fluid promote sciatic nerve regeneration?

Glioblastoma cyst fluid contains growth factors and extracellular matrix proteins which are known as neurotrophic and neurite-promoting agents. Therefore, we hypothesized that glioblastoma cyst fluid can promote the regeneration of injured peripheral nerves. To validate this hypothesis, we transected rat sciatic nerve, performed epineural anastomosis, and wrapped the injured sciatic nerve with glioblastoma cyst fluid- or saline-soaked gelatin sponges. Neurological function and histomorphological examinations showed that compared with the rats receiving local saline treatment, those receiving local glioblastoma cyst fluid treatment had better sciatic nerve function, fewer scars, greater axon area, counts and diameter as well as fiber diameter. These findings suggest that glioblastoma cyst fluid can promote the regeneration of injured sciatic nerve and has the potential for future clinical application in patients with peripheral nerve injury.

Animal models of erectile dysfunction

Erectile dysfunction (ED) is a prevalent male sexual dysfunction with profound adverse effects on the physical and the psychosocial health of men and, subsequently, on their partners. The expanded use of various types of rodent models has produced some advances in the study of ED, and neurophysiological studies using various animal models have provided important insights into human sexual dysfunction. At present, animal models play a key role in exploring and screening novel drugs designed to treat ED.

Effect of FK506 on apoptosis of facial motor neurons in rats and its possible mechanism

To investigate the effect of FK506 on apoptosis of facial motor neurons in rats and its possible mechanism. A total of 48 Wistar rats were randomly divided into experimental group and control group. Facial nerve injury model was established by transection of facial nerve at stylomastoid foramen. Rats in experimental group and control group were provided with FK506 and normal saline by intraperitoneal injection, respectively. The morphology of facial neurons was observed under light microscope at different time points after injury. Apoptotic facial motor neurons were detected by TdT-mediated dUTP-biotin nick and labeling (TUNEL) staining, and expression of bcl-2 and bax was evaluated by immunohistochemistry. After facial nerve transection, the apoptotic cells in experimental group significantly decreased compared to control group (P < 0.05), with higher expression of bcl-2 and lower expression of bax in experimental group. FK506 could inhibit apoptosis of facial motor neurons after facial nerve transection, possibly via up-regulation of bcl-2 expression and down-regulation of bax expression.

Profiling circulating microRNA expression in a mouse model of nerve allotransplantation

Background

The lack of noninvasive biomarkers of rejection remains a challenge in the accurate monitoring of deeply buried nerve allografts and precludes optimization of therapeutic intervention. This study aimed to establish the expression profile of circulating microRNAs (miRNAs) during nerve allotransplantation with or without immunosuppression.

Results

Balb/c mice were randomized into 3 experimental groups, that is, (1) untreated isograft (Balb/c → Balb/c), (2) untreated allograft (C57BL/6 → Balb/c), and (3) allograft (C57BL/6 → Balb/c) with FK506 immunosuppression. A 1-cm Balb/c or C57BL/6 donor sciatic nerve graft was transplanted into sciatic nerve gaps created in recipient mice. At 1, 3, 7, 10, and 14 d after nerve transplantation, nerve grafts, whole blood, and sera were obtained for miRNA expression analysis with an miRNA array and subsequent validation with quantitative real-time PCR (qRT-PCR). Three circulating miRNAs (miR-320, miR-762, and miR-423-5p) were identified in the whole blood and serum of the mice receiving an allograft with FK506 immunosuppression, within 2 weeks after nerve allotransplantation. However, these 3 circulating miRNAs were not expressed in the nerve grafts. The expression of all these 3 upregulated circulating miRNAs significantly decreased at 2, 4, and 6 d after discontinuation of FK506 immunosuppression. In the nerve graft, miR-125-3b and miR-672 were significantly upregulated in the mice that received an allograft with FK506 only at 7 d after nerve allotransplantation.

Conclusions

We identified the circulating miR-320, miR-762, and miR-423-5p as potential biomarkers for monitoring the immunosuppression status of the nerve allograft. However, further research is required to investigate the mechanism behind the dysregulation of these markers and to evaluate their prognostic value in nerve allotransplantation.

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.

Tissue engineered constructs for peripheral nerve surgery

BACKGROUND

Tissue engineering has been defined as "an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ". Traumatic peripheral nerve injury resulting in significant tissue loss at the zone of injury necessitates the need for a bridge or scaffold for regenerating axons from the proximal stump to reach the distal stump.

METHODS

A review of the literature was used to provide information on the components necessary for the development of a tissue engineered peripheral nerve substitute. Then, a comprehensive review of the literature is presented composed of the studies devoted to this goal.

RESULTS

Extensive research has been directed toward the development of a tissue engineered peripheral nerve substitute to act as a bridge for regenerating axons from the proximal nerve stump seeking the distal nerve. Ideally this nerve substitute would consist of a scaffold component that mimics the extracellular matrix of the peripheral nerve and a cellular component that serves to stimulate and support regenerating peripheral nerve axons.

CONCLUSIONS

The field of tissue engineering should consider its challenge to not only meet the autograft "gold standard" but also to understand what drives and inhibits nerve regeneration in order to surpass the results of an autograft.

Nerve regeneration in rat limb allografts: evaluation of acute rejection rescue

BACKGROUND

Successful nerve regeneration is critical to the functional success of composite tissue allografts. The present study was designed to characterize the effect of acute rejection on nerve regeneration and functional recovery in the setting of orthotopic limb transplantation.

METHODS

A rat orthotopic limb transplantation model was used to evaluate the effects of acute rejection on nerve regeneration and motor recovery. Continuous administration of FK506 (full suppression), administration of FK506 for the first 8 of 12 weeks (late rejection), or delayed administration of FK506/dexamethasone following noticeable rejection (early rejection) was used to preclude or induce rejection following limb transplantation. Twelve weeks postoperatively, nerve regeneration was assessed by means of histomorphometric analysis of explanted sciatic nerve, and motor recovery was assessed by means of evoked muscle force measurement in extensor digitorum longus muscle.

RESULTS

A single episode of acute rejection that occurs immediately or late after reconstruction does not significantly alter the number of regenerating axonal fibers. Acute rejection occurring late after reconstruction adversely affects extensor digitorum longus muscle function in composite tissue allografts.

CONCLUSIONS

Collected data reinforce that adequate immunosuppressant administration in cases of allogeneic limb transplantation ensures levels of nerve regeneration and motor functional recovery equivalent to that of syngeneic transplants. Prompt rescue following acute rejection was further demonstrated not to significantly affect nerve regeneration and functional recovery postoperatively. However, instances of acute rejection that occur late after reconstruction affect graft function. In total, the present study begins to characterize the effect of immunosuppression regimens on nerve regeneration and motor recovery in the setting of composite tissue allografts.

Effect of ginkgo biloba extract on recovery after facial nerve crush injury in the rat

BACKGROUND AND OBJECTIVE

Many pharmacological agents have shown successful results in experimental crush injury of the peripheral nerve. To date, therapeutic effect of ginkgo biloba extract (GBE) on the peripheral nerve crush injury of rats has been rarely reported, moreover, neuroprotective effect on the facial nerve crush injury has not been reported.

MATERIALS AND METHODS

Prospective functional recovery, using a vibrissae movement and electrophysiological analysis of recovery 4 weeks after the facial nerve crush in adult rats, and comparison with randomized intraperitoneal injection of either GBE or control phosphate buffered saline.

RESULTS

Relative to the control group (26 days post operation), administration of GBE significantly accelerated the recovery of vibrissae orientation to 11.7 days post the operation. A significant functional recovery was observed by postoperative 2nd week in the experimental group. The recovery of threshold and conduction velocity, postoperative 4th week in the experimental group, showed statistically significant difference compared to that of the control group.

CONCLUSION

From this result, intraperitoneal injection of GBE has been found effective in promoting the regeneration of the nerve in an experimental facial nerve crush rat model. Further studies, including morphological and molecular analyses, are necessary to clarify the mechanisms of GBE on the facial nerve crush.

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.

Sir-two-homolog 2 (Sirt2) modulates peripheral myelination through polarity protein Par-3/atypical protein kinase C (aPKC) signaling

The formation of myelin by Schwann cells (SCs) occurs via a series of orchestrated molecular events. We previously used global expression profiling to examine peripheral nerve myelination and identified the NAD(+)-dependent deacetylase Sir-two-homolog 2 (Sirt2) as a protein likely to be involved in myelination. Here, we show that Sirt2 expression in SCs is correlated with that of structural myelin components during both developmental myelination and remyelination after nerve injury. Transgenic mice lacking or overexpressing Sirt2 specifically in SCs show delays in myelin formation. In SCs, we found that Sirt2 deacetylates Par-3, a master regulator of cell polarity. The deacetylation of Par-3 by Sirt2 decreases the activity of the polarity complex signaling component aPKC, thereby regulating myelin formation. These results demonstrate that Sirt2 controls an essential polarity pathway in SCs during myelin assembly and provide insights into the association between intracellular metabolism and SC plasticity.

Effects of FK506 on Hippocampal CA1 Cells Following Transient Global Ischemia/Reperfusion in Wistar Rat

Transient global cerebral ischemia causes loss of pyramidal cells in CA1 region of hippocampus. In this study, we investigated the neurotrophic effect of the immunosuppressant agent FK506 in rat after global cerebral ischemia. Both common carotid arteries were occluded for 20 minutes followed by reperfusion. In experimental group 1, FK506 (6 mg/kg) was given as a single dose exactly at the time of reperfusion. In the second group, FK506 was administered at the beginning of reperfusion, followed by its administration intraperitoneally (IP) 6, 24, 48, and 72 hours after reperfusion. FK506 failed to show neurotrophic effects on CA1 region when applied as a single dose of 6 mg/kg. The cell number and size of the CA1 pyramidal cells were increased, also the number of cell death decreased in this region when FK506 was administrated 48 h after reperfusion. This work supports the possible use of FK506 in treatment of ischemic brain damage.

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.

Effect of sialodacryoadenitis virus infection on axonal regeneration

The effect of sialodacryoadenitis virus (SDAV) infection on axonal regeneration and functional recovery was investigated in male Lewis rats. Animals underwent unilateral tibial nerve transection, immediate repair, and treatment with either FK506 (treated) or control vehicle (untreated). Serial walking track analyses were performed to assess functional recovery. Nerves were harvested for morphometric analysis on postoperative day 18 after an SDAV outbreak occurred that affected the 12 experimental animals. Histomorphometry and walking track data were compared against 36 historical controls. Rats infected with SDAV demonstrated severely impaired axonal regeneration and diminished functional recovery. Total fiber counts, nerve density, and percent neural tissue were all significantly reduced in infected animals (P < 0.05). Active SDAV infection severely impaired nerve regeneration and negated the positive effect of FK506 on nerve regeneration in rats. Immunosuppressive risks must be weighed carefully against the potential neuroregenerative benefits in the treatment of peripheral nerve injuries.

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.

Role of chronic Schwann cell denervation in poor functional recovery after nerve injuries and experimental strategies to combat it

OBJECTIVE

To present our data about the role of chronic denervation (CD) of the distal nerve stumps as compared with muscle denervation atrophy and experimental strategies to promote better functional recovery.

METHODS

A rat model of nerve injury and repair was used. The common peroneal branch of the sciatic nerve was subjected to 0 to 24 weeks of CD before cross-suture with the tibial motoneurons. Our outcome measures included the numbers of motoneurons that regenerated their axons and the numbers that reinnervated muscle targets (motor units). To overcome the effects of CD, we used subcutaneous injection of FK506 and in vitro reactivation of Schwann cells that had been subjected to 24 weeks of CD with transforming growth factor beta.

RESULTS

Numbers of regenerated motoneurons and reinnervated motor units decreased as a function of duration of CD. However, axons that regenerated through the distal nerve stumps reinnervated the muscle targets and even formed enlarged motor unit size regardless of the duration of CD. FK506 doubled the numbers of tibial motoneurons that regenerated their axons into the common peroneal nerve even after delayed repair. Reactivation of chronically denervated Schwann cells with transforming growth factor beta significantly increased their capacity to support axonal regeneration.

CONCLUSION

CD of the distal nerve stumps is the primary factor that results in poor axonal regeneration and subsequently poor functional recovery. Acceleration of the rate of axonal regeneration and/or reactivation of Schwann cells of the distal nerve stumps are effective experimental strategies to promote axonal regeneration and functional recovery.

Tacrolimus (FK506): Safety and Applications in Reconstructive Surgery

Tacrolimus (FK506) is a macrolide immunosuppressive drug that is approved for the prevention of allograft rejection. It is a standard component of immunosuppressive regimens currently in use for organ and reconstructive tissue transplants. The experimental literature has demonstrated potential efficacy in the management of other diseases for which transplantation does not play a role. The ability of tacrolimus to modulate the immune system and inhibit T cell activation provides a potential benefit for the treatment of disorders in which autoimmune phenomena are central to their pathogenesis such as rheumatoid arthritis and inflammatory bowel disease. Tacrolimus also has well-established neuroprotective and neuroregenerative properties through both similar and different mechanisms that have been extensively demonstrated in both small and large animal models. However, as a potent immunosuppressive agent, it can cause serious adverse effects, some of which are irreversible and potentially life threatening. This article reviews its safety under different therapeutic requirements and applications in both allogeneic and autogenous tissue reconstruction.

Pathophysiology of nerve regeneration and nerve reconstruction in burned patients

In extensive burns peripheral nerves can be involved. The injury to the nerve can be direct by thermal or electrical burns, but nerves can also be indirectly affected by the systemic reaction that follows the burn. Mediators will be released causing a neuropathy to nerves remote from the involved area. Involved mediators and possible therapeutic options will be discussed. In burned patients nerves can be reconstructed using autologous nerve grafts or nerve conduits. A key factor is an adequate wound debridement and a well-vascularized bed to optimize the outgrowth of the axons. Early free tissue transfers have shown promising results.