Low-Dose FK506 After Contralateral C7 Transfer to the Musculocutaneous Nerve Using Two Different Tubes: A Study in Rats

Approach to management of nerve gaps in peripheral nerve injuries

Peripheral nerve injuries (PNI) are a major clinical problem. In general, PNI results from motor vehicle accidents, lacerations with sharp objects, penetrating trauma (gunshot wounds) and stretching or crushing trauma and fractures. They can result in significant morbidity, including motor and/or sensory loss, which can affect significantly the life of the patient. Currently, the standard surgical technique for complete nerve transection is end-to-end neurorrhaphy. Unfortunately, there is segmental loss of the nerve trunk in some cases where nerve mobilization may permit end-to-end neurorrhaphy if the gap is less than 1 cm. When the nerve gap exceeds 1 cm, autologous nerve grafting is the gold standard of treatment. But in light of limited availability and concerned donor site morbidity, other techniques have been used: vascularized nerve grafts, cellular and acellular allografts, nerve conduits, nerve transfers and end-to-side neurorrhaphy. This review intends to present an overview of the literature on the applications of these techniques in repair of peripheral nerve injuries. This article also focuses on preoperative assessment, surgical timing, available options and future perspectives.

The Surgical Management of Nerve Gaps: Present and Future

Peripheral nerve injuries can result in significant morbidity, including motor and/or sensory loss, which can affect significantly the life of the patient. Nowadays, the gold standard for the treatment of nerve section is end-to-end neurorrhaphy. Unfortunately, in some cases, there is segmental loss of the nerve trunk. Nerve mobilization allows primary repair of the sectioned nerve by end-to-end neurorrhaphy if the gap is less than 1 cm. When the nerve gap exceeds 1 cm, autologous nerve grafting is the gold standard of treatment. To overcome the limited availability and the donor site morbidity, other techniques have been used: vascularized nerve grafts, cellular and acellular allografts, nerve conduits, nerve transfers, and end-to-side neurorrhaphy. The purpose of this review is to present an overview of the literature on the applications of these techniques in peripheral nerve repair. Furthermore, preoperative evaluation, timing of repair, and future perspectives are also discussed.

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.

Comparison of nerve, vessel, and cartilage grafts in promoting peripheral nerve regeneration

Peripheral nerve injury primarily occurs due to trauma as well as factors such as tumors, inflammatory diseases, congenital deformities, infections, and surgical interventions. The surgical procedure to be performed as treatment depends on the etiology, type of injury, and the anatomic region. The goal of treatment is to minimize loss of function due to motor and sensory nerve loss at the distal part of the injury. Regardless of the cause of the injury, the abnormal nerve regeneration due to incomplete nerve regeneration, optimal treatment of peripheral nerve injuries should provide adequate coaptation of proximal and distal sides without tension, preserving the neurotrophic factors within the repair line. The gold standard for the treatment of nerve defects is the autograft; however, due to denervation of the donor site, scarring, and neuroma formation, many studies have aimed to develop simpler methods, better functional results, and less morbidity. In this study, a defect 1 cm in length was created on the sciatic nerve of rats. The rats were treated with the following procedures: group 1, autograft; group 2, allogeneic aorta graft; group 3, diced cartilage graft in allogeneic aorta graft; and group 4, tubularized cartilage graft in allogeneic aorta graft. Group 5 was the control group. The effects of cartilage tissue in nerve regeneration were evaluated by functional and histomorphological methods.Group 1, for which the repair was performed with an autograft, was evaluated to be the most similar to the control group. There was not a statistically significant difference in myelination and Schwann cell rates between group 2, in which an allogeneic aorta graft was used, and group 3, in which diced cartilage in an allogeneic aorta graft was used. In group 4, myelination and Schwann cell formation were observed; however, they were scattered and irregular, likely due to increased fibrosis.In all of the groups, nerve regeneration at various rates was observed both functionally and histomorphologically. This study demonstrates that cartilage tissue has promoting effects in nerve regeneration.

Improving peripheral nerve regeneration: from molecular mechanisms to potential therapeutic targets

Peripheral nerve injury is common especially among young individuals. Although injured neurons have the ability to regenerate, the rate is slow and functional outcomes are often poor. Several potential therapeutic agents have shown considerable promise for improving the survival and regenerative capacity of injured neurons. These agents are reviewed within the context of their molecular mechanisms. The PI3K/Akt and Ras/ERK signaling cascades play a key role in neuronal survival. A number of agents that target these pathways, including erythropoietin, tacrolimus, acetyl-l-carnitine, n-acetylcysteine and geldanamycin have been shown to be effective. Trk receptor signaling events that up-regulate cAMP play an important role in enhancing the rate of axonal outgrowth. Agents that target this pathway including rolipram, testosterone, fasudil, ibuprofen and chondroitinase ABC hold considerable promise for human application. A tantalizing prospect is to combine different molecular targeting strategies in complementary pathways to optimize their therapeutic effects. Although further study is needed prior to human trials, these modalities could open a new horizon in the clinical arena that has so far been elusive.

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.

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.