Effects of cyclosporin A and predegeneration on survival and regeneration of peripheral nerve allografts in rabbits

Functional and immunological peculiarities of peripheral nerve allografts

This review addresses the accumulating evidence that live (not decellularized) allogeneic peripheral nerves are functionally and immunologically peculiar in comparison with many other transplanted allogeneic tissues. This is relevant because live peripheral nerve allografts are very effective at promoting recovery after segmental peripheral nerve injury via axonal regeneration and axon fusion. Understanding the immunological peculiarities of peripheral nerve allografts may also be of interest to the field of transplantation in general. Three topics are addressed: The first discusses peripheral nerve injury and the potential utility of peripheral nerve allografts for bridging segmental peripheral nerve defects via axon fusion and axon regeneration. The second reviews evidence that peripheral nerve allografts elicit a more gradual and less severe host immune response allowing for prolonged survival and function of allogeneic peripheral nerve cells and structures. Lastly, potential mechanisms that may account for the immunological differences of peripheral nerve allografts are discussed.

The Median Nerve Injury Model in Pre-clinical Research - A Critical Review on Benefits and Limitations

The successful introduction of innovative treatment strategies into clinical practise strongly depends on the availability of effective experimental models and their reliable pre-clinical assessment. Considering pre-clinical research for peripheral nerve repair and reconstruction, the far most used nerve regeneration model in the last decades is the sciatic nerve injury and repair model. More recently, the use of the median nerve injury and repair model has gained increasing attention due to some significant advantages it provides compared to sciatic nerve injury. Outstanding advantages are the availability of reliable behavioural tests for assessing posttraumatic voluntary motor recovery and a much lower impact on the animal wellbeing. In this article, the potential application of the median nerve injury and repair model in pre-clinical research is reviewed. In addition, we provide a synthetic overview of a variety of methods that can be applied in this model for nerve regeneration assessment. This article is aimed at helping researchers in adequately adopting this in vivo model for pre-clinical evaluation of peripheral nerve reconstruction as well as for interpreting the results in a translational perspective.

Early cyclosporin A treatment retards axonal degeneration in an experimental peripheral nerve injection injury model

Injury to peripheral nerves during injections of therapeutic agents such as penicillin G potassium is common in developing countries. It has been shown that cyclosporin A, a powerful immunosuppressive agent, can retard Wallerian degeneration after peripheral nerve crush injury. However, few studies are reported on the effects of cyclosporin A on peripheral nerve drug injection injury. This study aimed to assess the time-dependent efficacy of cyclosporine-A as an immunosuppressant therapy in an experimental rat nerve injection injury model established by penicillin G potassium injection. The rats were randomly divided into three groups based on the length of time after nerve injury induced by cyclosporine-A administration (30 minutes, 8 or 24 hours). The compound muscle action potentials were recorded pre-injury, early post-injury (within 1 hour) and 4 weeks after injury and compared statistically. Tissue samples were taken from each animal for histological analysis. Compared to the control group, a significant improvement of the compound muscle action potential amplitude value was observed only when cyclosporine-A was administered within 30 minutes of the injection injury (P < 0.05); at 8 or 24 hours after cyclosporine-A administration, compound muscle action potential amplitude was not changed compared with the control group. Thus, early immunosuppressant drug therapy may be a good alternative neuroprotective therapy option in experimental nerve injection injury induced by penicillin G potassium injection.

Immunosuppressive effect of 15-deoxyspergualin applied to peripheral nerve allotransplantation in the rat

15-Deoxyspergualin (15-DSG), which has a unique immunosuppressive action, was applied to peripheral nerve allotransplantation. Its effects on graft survival were experimentally assessed using inbred rats. The sciatic nerve (20 mm) allotransplantation model was created in two different strains. An attempt was made to answer the following two questions: (1) can short-term immunosuppression alone produce sufficient immunological tolerance to maintain graft survival indefinitely? (2) can graft rejection be prevented by chronic intermittent low-dose 15-DSG administration (2.5 mg/kg/day), and to what extent does nerve regeneration occur? To evaluate the efficacy of 15-DSG, a comparison was made with autografts, allografts with no immunosuppression, and allografts immunosuppressed with cyclosporine (CsA), a strong immunosuppressant. The results indicate that short-term 15-DSG therapy is incapable of inducing immunotolerance of peripheral nerve allografts. Because nerve conduction in the rejected allografts was better preserved than in the CsA group, short-course 15-DSG therapy appeared to provide better results than CsA therapy for peripheral nerve allotransplantation.

Nerve regenerating effect of short-course administration of cyclosporine after fresh peripheral nerve allotransplantation in the rat: comparison of nerve regeneration using different forms of donor nerve allografts

There is almost universal agreement that if cyclosporine (CsA), which is a potent immunosuppressant, is temporarily administered after surgery, regenerated axons will be maintained even after withdrawal of CsA following peripheral nerve allotransplantation. Thus, this experimental study was conducted to investigate whether a difference in donor nerve form, including thickness and length, influences nerve regeneration after withdrawal of immunosuppression with CsA. The findings suggest that as a result of immunosuppression with CsA, large-diameter nerve grafts are better able to induce nerve regeneration than small-diameter grafts, and after withdrawal of the immunosuppressant, thick nerve grafts are also better able to preserve regenerated axons against the rejection reaction than thin grafts. With regard to the length of the grafted nerve, short nerve allografts yield higher axon counts than long ones, the same as with autografts. The best way to induce nerve regeneration appears to be to transplant a short, thick nerve allograft, which is definitely capable of inducing many regenerated axons.

Observations on the blood and perineurial permeability barriers of surviving nerve allografts in immunodeficient and immunosuppressed rats

The authors investigate whether there are any permeability changes in the endoneurial blood-nerve barrier and the perineurium-nerve barrier of surviving nerve allografts. In a normal nerve, the blood-nerve barrier regulates the passage of substances from endoneurial blood vessels into the endoneurium, whereas the perineurium-nerve barrier protects the endoneurium from agents that escape from permeable epineurial vessels and accumulate around the nerve. Nerves from ACI rats were transplanted into immunologically deficient nude rats or normal Fischer rats immunosuppressed with cyclosporin A. None of the nerve allografts was rejected. The blood-nerve barrier of nerve allografts at 2 and 6 weeks postoperatively was permeable to intravenously injected horseradish peroxidase, which spread into endoneurial tissue. Electron microscopy revealed that horseradish peroxidase escaped from endoneurial vessels through intercellular junctions between endothelial cells. At 24 weeks, the blood-nerve barrier of nerve allografts had recovered and the endoneurial vessels, like those in normal nerves, were impermeable to horseradish peroxidase. The perineurium-nerve barrier of nerve allografts remained impermeable to horseradish peroxidase at all times. Axons were grouped into numerous minifascicles at nerve anastomosis zones at 24 weeks. Each nerve fascicle was surrounded by an impermeable perineurium. These results demonstrate that regenerated axons in long-term surviving nerve allografts and at anastomosis zones are protected by permeability barriers. It is concluded that permeability barriers of nerve allografts are not permanently altered by a foreign environment (grafts to nude rats) even when immunosuppression with cyclosporin A is required to prevent allograft rejection (grafts to Fischer rats).