Extracts obtained from predegenerated nerves improve functional recovery after sciatic nerve transection

Role of shortwave and microwave diathermy in peripheral neuropathy

Objective

This study was performed to review the current evidence for the efficacy of shortwave and microwave diathermy in promoting nerve regeneration after peripheral nerve injuries in both animal models and human patients.

Methods

An extensive literature search was conducted without publication data restrictions. Studies including the intervention and outcome in animal or human models were selected. Non-English studies, reviews, letters, and case reports were excluded.

Results

Eleven articles were included in this study. Shortwave diathermy at the frequency of 27.12 or 40.68 MHz was used in six of seven animal studies, while only one study utilized microwave diathermy at 915 MHz. Seven animal experiments demonstrated that shortwave or microwave diathermy produces an increased myelinated nerve fiber number, myelin sheath thickness, and axon diameter as well as improved electrophysiological parameters and locomotion. A total of 128 patients (207 wrists) were enrolled in four clinical studies. The clinical use of diathermy in human patients with carpal tunnel syndrome showed positive effects on pain, hand function, and electrophysiological findings.

Conclusions

Shortwave or microwave diathermy can improve the electrophysiological parameters, myelinated fiber number, and axon diameter of the injured nerve.

Application of peripheral nerve conduits in clinical practice: A literature review

Understanding the pathomechanisms behind peripheral nerve damage and learning the course of regeneration seem to be crucial for selecting the appropriate methods of treatment. Autografts are currently the gold standard procedure in nerve reconstruction. However, due to the frequency of complications resulting from autografting and a desire to create a better environment for the regeneration of the damaged nerve, artificial conduits have become an approved alternative treatment method. The aim of this mini-review is to present the nerve scaffolds that have been applied in clinical practice to date, and the potential directions of developments in nerve conduit bioengineering. Articles regarding construction and characterization of nerve conduits were used as the theoretical background. All papers, available in PubMed database since 2000, presenting results of application of artificial nerve conduits in clinical trials were included into this mini-review. Fourteen studies including ≤10 patients and 10 trials conducted on >10 patients were analyzed as well as 24 papers focused on artificial nerve conduits per se. Taking into consideration the experiences of the authors investigating nerve conduits in clinical trials, it is essential to point out the emergence of bioresorbable scaffolds, which in the future may significantly change the treatment of peripheral nerve injuries. Also worth mentioning among the advanced conduits are hybrid conduits, which combine several modifications of a synthetic material to provide the optimal regeneration of a damaged nerve.

Synergistic effects of ultrashort wave and bone marrow stromal cells on nerve regeneration with acellular nerve allografts

Acellular nerve allografts (ANA) possess bioactivity and neurite promoting factors in nerve tissue engineering. Previously we reported that low dose ultrashort wave (USW) radiation could enhance the rate and quality of peripheral nerve regeneration with ANA repairing sciatic nerve defects. Meanwhile, ANA implanted with bone marrow stromal cells (BMSCs) exhibited a similar result. Thus, it is interesting to know whether it might yield a synergistic effect when USW radiation is combined with BMSCs-laden ANA. Here we investigated the effectiveness of ANA seeded with BMSCs, combined with USW therapy on repairing peripheral nerve injuries. Adult male Wistar rats were randomly divided into four groups: Dulbecco's modified Eagle's medium (DMEM) control group, BMSCs-laden group, ultrashort wave (USW) group and BMSC + USW group. The regenerated nerves were assayed morphologically and functionally, and growth-promoting factors in the regenerated tissues following USW administration or BMSCs integration were also detected. The results indicated that the combination therapy caused much better beneficial effects evidenced by increased myelinated nerve fiber number, myelin sheath thickness, axon diameter, sciatic function index, nerve conduction velocity, and restoration rate of tibialis anterior wet weight. Moreover, the mRNA levels of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) in the spinal cord and muscles were elevated significantly. In conclusion, we found a synergistic effect of USW radiation and BMSCs treatment on peripheral nerve regeneration, which may help establish novel strategies for repairing peripheral nerve defects.

Fibrin matrices with affinity-based delivery systems and neurotrophic factors promote functional nerve regeneration

Glial-derived neurotrophic factor (GDNF) and nerve growth factor (NGF) have both been shown to enhance peripheral nerve regeneration following injury and target different neuronal populations. The delivery of either growth factor at the site of injury may, therefore, result in quantitative differences in motor nerve regeneration and functional recovery. In this study we evaluated the effect of affinity-based delivery of GDNF or NGF from fibrin-filled nerve guidance conduits (NGCs) on motor nerve regeneration and functional recovery in a 13 mm rat sciatic nerve defect. Seven experimental groups were evaluated consisting of GDNF or NGF and the affinity-based delivery system (DS) within NGCs, control groups excluding the DS and/or growth factor, and nerve isografts. Groups with growth factor in the conduit demonstrated equivalent or superior performance in behavioral tests and relative muscle mass measurements compared to isografts at 12 weeks. Additionally, groups with GDNF demonstrated greater specific twitch and tetanic force production in extensor digitorum longus (EDL) muscle than the isograft control, while groups with NGF produced demonstrated similar force production compared to the isograft control. Assessment of motor axon regeneration by retrograde labeling further revealed that the number of ventral horn neurons regenerating across NGCs containing GDNF and NGF DS was similar to the isograft group and these counts were greater than the groups without growth factor. Overall, the GDNF DS group demonstrated superior functional recovery and equivalent motor nerve regeneration compared to the isograft control, suggesting it has potential as a treatment for motor nerve injury.

Heparin-binding-affinity-based delivery systems releasing nerve growth factor enhance sciatic nerve regeneration

The controlled delivery of nerve growth factor (NGF) to the peripheral nervous system has been shown to enhance nerve regeneration following injury, although the effect of release rate has not been previously studied with an affinity-based delivery system (DS). The goal of this research was to determine if the binding site affinity of the DS affected nerve regeneration in vivo using nerve guidance conduits (NGCs) in a 13-mm rat sciatic nerve defect. These DSs consisted of bi-domain peptides that varied in heparin-binding affinity, heparin and NGF, which binds to heparin with moderate affinity. Eight experimental groups were evaluated consisting of NGF with DS, control groups excluding one or more components of the DS within silicone conduits and nerve isografts. Nerves were harvested 6 weeks after treatment for analysis by histomorphometry. These DSs with NGF resulted in a higher frequency of nerve regeneration compared to control groups and were similar to the nerve isograft group in measures of nerve fiber density and percent neural tissue, but not in total nerve fiber count. In addition, these DSs with NGF contained a significantly greater percentage of larger diameter nerve fibers, suggesting more mature regenerating nerve content. While there were no differences in nerve regeneration due to varying peptide affinity with these DSs, their use with NGF enhanced peripheral nerve regeneration through a NGC across a critical nerve gap.

Affinity-based release of glial-derived neurotrophic factor from fibrin matrices enhances sciatic nerve regeneration

Glial-derived neurotrophic factor (GDNF) promotes both sensory and motor neuron survival. The delivery of GDNF to the peripheral nervous system has been shown to enhance regeneration following injury. In this study, we evaluated the effect of affinity-based delivery of GDNF from a fibrin matrix in a nerve guidance conduit on nerve regeneration in a 13 mm rat sciatic nerve defect. Seven experimental groups were evaluated which received GDNF or nerve growth factor (NGF) with the delivery system within the conduit, control groups excluding one or more components of the delivery system, and nerve isografts. Nerves were harvested 6 weeks after treatment for analysis by histomorphometry and electron microscopy. The use of the delivery system (DS) with either GDNF or NGF resulted in a higher frequency of nerve regeneration vs. control groups, as evidenced by a neural structure spanning the 13 mm gap. The GDNF DS and NGF DS groups were also similar to the nerve isograft group in measures of nerve fiber density, percent neural tissue and myelinated area measurements, but not in terms of total fiber counts. In addition, both groups contained a significantly greater percentage of larger diameter fibers, with GDNF DS having the largest in comparison to all groups, suggesting more mature neural content. The delivery of GDNF via the affinity-based delivery system can enhance peripheral nerve regeneration through a silicone conduit across a critical nerve gap and offers insight into potential future alternatives to the treatment of peripheral nerve injuries.

Impact of different types of facial nerve reconstruction on the recovery of motor function: an experimental study in adult rats

OBJECTIVE

Poor functional recovery after facial nerve reconstruction is characterized by mass movements and synkinesis. Major reasons are axonal sprouting from the regenerating axons leading to misdirected reinnervation and hyperinnervation as well as polyinnervation of the mimic muscle end plates. We analyzed whether or not the type of nerve reconstruction influenced these pathological phenomena.

METHODS

The experiments were performed on 48 adult rats divided into four groups. One group served as an intact control and the experimental groups were subjected to facial-facial nerve repair (FFN), facial nerve interpositional grafting, and hypoglossal-facial nerve repair (HFN), with 12 subjects in each group. Two months later, functional recovery was measured by biometrical motion analysis of whisking. Retrograde fluorescence labeling of the brainstem motoneurons was used to quantify the degree of collateral axonal branching at the lesion site. Fluorescence histochemistry of sections through the levator labii superioris muscle was performed to quantify the degree of polyinnervation after surgery.

RESULTS

The type of nerve reconstruction significantly influenced the regeneration. The whisking amplitude did not recover completely regardless of the type of reconstruction. The angular velocity and angular acceleration of the vibrissal hairs showed a full recovery after facial nerve interpositional grafting and HFN, whereas these parameters remained decreased after FFN. Significantly less collateral branching and polyinnervation of the end plates were determined after grafting and HFN than after FFN.

CONCLUSION

No type of immediate facial nerve reconstruction results in a full recovery in the rat. However, the morphological and functional recovery was significantly better after grafting and HFN than after FFN.

Hyperbaric oxygenation in peripheral nerve repair and regeneration

Peripheral nerves are essential connections between the central nervous system and muscles, autonomic structures and sensory organs. Their injury is one of the major causes for severe and longstanding impairment in limb function. Acute peripheral nerve lesion has an important inflammatory component and is considered as ischemia-reperfusion (IR) injury. Surgical repair has been the standard of care in peripheral nerve lesion. It has reached optimal technical development but the end results still remain unpredictable and complete functional recovery is rare. Nevertheless, nerve repair is not primarily a mechanical problem and microsurgery is not the only key to success. Lately, there have been efforts to develop alternatives to nerve graft. Work has been carried out in basal lamina scaffolds, biologic and non-biologic structures in combination with neurotrophic factors and/or Schwann cells, tissues, immunosuppressive agents, growth factors, cell transplantation, principles of artificial sensory function, gene technology, gangliosides, implantation of microchips, hormones, electromagnetic fields and hyperbaric oxygenation (HBO). HBO appears to be a beneficial adjunctive treatment for surgical repair in the acute peripheral nerve lesion, when used at lower pressures and in a timely fashion (<6 hours).

Overexpression of copper/zinc-superoxide dismutase in transgenic mice markedly impairs regeneration and increases development of neuropathic pain after sciatic nerve injury

Despite the general capacity of peripheral nervous system to regenerate, peripheral nerve injury is often followed by incomplete recovery of function, sometimes with the burden of neuropathic pain. The mechanisms of both regeneration and nociception have not been clarified, but it is known that inflammatory reactions are involved. Cu/Zn-superoxide dismutase (SOD1) is an important scavenger protein that acts against oxidative stress. It has been shown to play an important role in apoptosis and inflammation. The aim of this study was to examine the role of SOD1 overexpression in peripheral nerve regeneration and neuropathic pain-related behavior in mice. Sciatic nerves of SOD1-overexpressing and FVB/N wild type-mice were transected and immediately resutured. Evaluation of motor and sensory function and autotomy was carried out during 4 weeks of followup. We found markedly worse sciatic function index outcome as well as more significant atrophy of denervated muscles in SOD1-overexpressing animals compared with wild type. Autotomy was markedly worse in SOD1 transgenic mice than in wild-type animals. Histological evaluation revealed that the intensity of regeneration features, including numbers of GAP-43-positive growth cones, Schwann cells, and macrophages in the distal stump of the transected nerve, was also decreased in transgenic mice. Neuroma formation at the injury site was significantly more prominent in this group. Taken together, our findings suggest that SOD1 overexpression is deleterious for nerve regeneration processes and aggravates neuropathic pain-like state in mice. This can be at least partially ascribed to disturbed inflammatory reactions at the injury site.