Therapeutic strategies in promoting peripheral nerve regeneration

Peripheral Nerve Reconstruction with Bioabsorbable Polyphosphazene Conduits

Tubes of poly[bis(ethylalanato)phosphazene], obtained by evaporating the polymer around a 1.3 mm diameter capillary, were evaluated as guides for nerve regeneration in an experimental animal model. In six Wistar rats, under general anesthesia and with microsurgical technique, the ischiatic nerve was bilaterally isolated. On the right side, a segment was removed to create a defect of 10 mm, that was repaired with the conduit; on the left side the defect was repaired with harvested nerve segment from the right side. Controls at 30, 90, 180 days showed slow and gradual absorption of the conduit without signs of local or general toxicity. Nerve fiber regeneration in the conduits was not significantly different from that obtained with autologous grafts. Polyphosphazene conduits may be considered effective as a guide for nerve regeneration mainly in the perspective of using the polymer matrix as a carrier for neurite-promoting factors.

Evaluation of peripheral nerve regeneration across an 80-mm gap using a polyglycolic acid (PGA)--collagen nerve conduit filled with laminin-soaked collagen sponge in dogs

We evaluated peripheral nerve regeneration using a novel artificial nerve conduit. The conduit was made of a polyglycolic acid(PGA) - collagen tube filled with laminin- soaked collagen sponge. We implanted this nerve conduit across an 80mm gap in the peroneal nerve of dogs. Histological observation 12 months after implantation showed numerous unmyelinated and myelinated nerve fibershad regenerated beyond the gap. Neurofilaments were widely observed immunohistochemically in the regenerated nerve segments. These findings indicated that newly regenerated axons had extended across the gap and connected into the distal nerve segments. Compound muscle action potentials(CMAPs) and somatosensory evoked potentials (SEPs) were recorded in all dogs. At 12 months, the CMAPs indicated complete recovery, while the SEPs showed incomplete but substantial recovery. Walking patterns had returned to near-normal 12 months after implantation. Use of this nerve conduit can lead to peripheral nerve elongation and favorable functional recovery across a wider nerve gap.

Morphometric and ultrastructural studies of the sciatic nerve regeneration in rats intoxicated with ethanol

The aim of the study was to examine the process of sciatic nerve regeneration and changes in the dorsal root ganglia (from which sensory fibres of the sciatic nerve extend) in animals intoxicated with ethanol. The experiment used 20 rats, divided into two groups: control and treated. The treated animals were intragastrically given 2g/kg b.w. of ethanol in 25% aqueous solution. In both groups the right sciatic nerve was transected and then sutured. After 5 months the animals were anaesthetized. The left and the right spinal dorsal ganglia-L5 and sections from the non-operated and operated sciatic nerves were collected for analysis. Ultrastructural examinations and morphometric measurements were conducted. It was found that ethanol administrated to rats inhibited regeneration of the transected and then sutured sciatic nerve, impairing the growth of axons in the transected nerve and destroying the regenerating sensory ganglion cells. The mechanism of the changes described may be associated with axonal transport disorders or with the suppressed production of biologically active substances, which affect nerve regeneration.

Peripheral nerve injury and repair

Peripheral nerve injuries are common, and there is no easily available formula for successful treatment. Incomplete injuries are most frequent. Seddon classified nerve injuries into three categories: neurapraxia, axonotmesis, and neurotmesis. After complete axonal transection, the neuron undergoes a number of degenerative processes, followed by attempts at regeneration. A distal growth cone seeks out connections with the degenerated distal fiber. The current surgical standard is epineurial repair with nylon suture. To span gaps that primary repair cannot bridge without excessive tension, nerve-cable interfascicular auto-grafts are employed. Unfortunately, results of nerve repair to date have been no better than fair, with only 50% of patients regaining useful function. There is much ongoing research regarding pharmacologic agents, immune system modulators, enhancing factors, and entubulation chambers. Clinically applicable developments from these investigations will continue to improve the results of treatment of nerve injuries.

Peripheral nerve regeneration: comparison of laminin and acidic fibroblast growth factor

PURPOSE

In an effort to show the differences between neurotrophic factors, laminin and acidic fibroblast growth factor (aFGF) were compared in terms of their abilities to regenerate axons in vivo over an extended distance.

MATERIALS AND METHODS

The sciatic nerve was transected in 15 Sprague-Dawley rats. A 15-mm Silastic tube (Dow Corning, Midland, MI) was placed between the ends of the cut nerve and filled with either laminin, aFGF, or buffer applied to collagen sponges.

RESULTS

Ten weeks postimplantation, mean axon counts showed that both laminin (2432) and aFGF (1612) produced significantly higher numbers of axons than controls (1009) (P < .05) and that laminin showed significantly more nerve regeneration than aFGF (P < .05).

CONCLUSION

These results indicate that laminin and aFGF enhance peripheral nerve regeneration across a large gap, presumably through their neurotrophic effects and mitogenic properties on supporting cells. Furthermore, it is concluded that the transient nature of aFGF's effect on the regenerative environment limits its effectiveness at regenerating axons over a prolonged period of time.

Gangliosides and Guillain-Barré syndrome

Cases of Guillain-Barré syndrome (GBS) associated with parenteral use of gangliosides have been reported in several European countries. To evaluate the hypothesis of association between ganglioside exposure and occurrence of GBS, a case-control study was conducted. GBS cases discharged during 1989 from public and private hospitals in three Italian provinces were identified: 42 GBS cases and 420 controls matched on age and gender were enrolled. Data of onset of symptoms of GBS was taken from clinical records. Exposure status of subjects was ascertained through the regional computerized drug prescription monitoring system. The odds ratio of association between ganglioside use, in the 30 days prior to onset of symptoms, and GBS was 9.1 (95% confidence interval 2.8-29.4). Although there are formidable difficulties in distinguishing prodromal therapy of GBS from drug causation, the association with ganglioside therapy is strong and supportive of the hypothesis of a role of ganglioside preparations in the occurrence of GBS.

The effect of MS-818, a pyrimidine compound, on the regeneration of peripheral nerve fibers of mice after a crush injury

One of the pyrimidine compounds, 2-piperadino-6-methyl-5-oxo-5,6- dihydro(7H)pyrrolo[3,4-d]pyrimidine (MS-818), has neurotropic effects in vitro. Therefore, we studied the effect of MS-818 on the regeneration of the peroneal nerve in C57BL/6J mice after a crush injury. Two test groups, which received a daily intraperitoneal injection of 5 mg/kg or 10 mg/kg MS-818, respectively, were compared with controls, which received daily intraperitoneal injections of physiological saline, over a 14-day period. The maximum foot-width ratio (crushed side/uncrushed side) was obtained on days 1, 8 and 14 after the crush injury, and the various morphometric parameters were evaluated at both 5 and 10 mm distal to the proximal portion of the crush site. The significant effects of MS-818 included a larger maximum foot width (P < 0.04) and a greater number of unmyelinated axons per nerve at both levels (P < 0.003) in both test groups than in controls. MS-818 had no significant effects on body weight, the increase of total transverse fascicular area after the crush injury, the total number of myelinated fibers with their size distributions, or the number of nuclei of Schwann cells and macrophages. Therefore, we conclude that MS-818 promotes axonal sprouting and elongation after a crush injury in mice.

Ultra-high dose methylcobalamin promotes nerve regeneration in experimental acrylamide neuropathy

Despite intensive searches for therapeutic agents, few substances have been convincingly shown to enhance nerve regeneration in patients with peripheral neuropathies. Recent biochemical evidence suggests that an ultra-high dose of methylcobalamin (methyl-B12) may up-regulate gene transcription and thereby protein synthesis. We examined the effects of ultra-high dose of methyl-B12 on the rate of nerve regeneration in rats with acrylamide neuropathy, using the amplitudes of compound muscle action potentials (CMAPs) after tibial nerve stimulation as an index of the number of regenerating motor fibers. After intoxication with acrylamide, all the rats showed equally decreased CMAP amplitudes. The animals were then divided into 3 groups; rats treated with ultra-high (500 micrograms/kg body weight, intraperitoneally) and low (50 micrograms/kg) doses of methyl-B12, and saline-treated control rats. Those treated with ultra-high dose showed significantly faster CMAP recovery than saline-treated control rats, whereas the low-dose group showed no difference from the control. Morphometric analysis revealed a similar difference in fiber density between these groups. Ultra-high doses of methyl-B12 may be of clinical use for patients with peripheral neuropathies.

Homeodomain proteins in development and therapy

Homeobox genes encode transcriptional regulators found in all organisms ranging from yeast to humans. In Drosophila, a specific class of homeobox genes, the homeotic genes, specifies the identity of certain spatial units of development. Their genomic organization, in Drosophila, as well as in vertebrates, is uniquely connected with their expression which follows a 5'-posterior-3'-anterior rule along the longitudinal body axis. The 180-bp homeobox is part of the coding sequence of these genes, and the sequence of 60 amino acids it encodes is referred to as the homeodomain. Structural analyses have shown that homeodomains consist of a helix-turn-helix motif that binds the DNA by inserting the recognition helix into the major groove of the DNA and its amino-terminal arm into the adjacent minor groove. Developmental as well as gene regulatory functions of homeobox genes are discussed, with special emphasis on one group, the Antennapedia (Antp) class homeobox genes and a representative 60-amino acid Antennapedia peptide (pAntp). In cultured neuronal cells, pAntp translocates through the membrane specifically and efficiently and accumulates in the nucleus. The internalization process is followed by a strong induction of neuronal morphological differentiation, which raises the possibility that motoneuron growth is controlled by homeodomain proteins. It has been demonstrated that chimeric peptide molecules encompassing pAntp are also captured by cultured neurons and conveyed to their nuclei. This may be of enormous interest for the internalization of drugs.

A model of nerve regeneration in diabetic neuropathy

The continued difficulty in discovering the cause of diabetic neuropathy may be due to the fact that researchers persist in looking for a factor associated with diabetes mellitus which damages nerves. The hypothesis that diabetic neuropathy is in fact related to some diabetes-related factor which slows nerve regeneration seems to fit the observed facts better. A model of nerve regeneration in diabetic neuropathy is presented, which facilitates understanding of recently published data on nerve regeneration in human diabetics.

ACTH/MSH(4-10) analog BIM 22015 aids regeneration via neurotrophic and myotrophic attributes

Structural differences between noncorticotropic ACTH peptides result in marked differences in their effects on regenerating nerve and muscle in rats. The ACTH/MSH(4-10) analog BIM 22015 was administered IP in dosages from 0.1 to 40 micrograms/kg/48 h for 5, 7, or 11 days after peroneal nerve crush, and characteristics of extensor digitorum longus (EDL) muscle were studied and compared with ACTH/MSH(4-10). Eleven days postcrush 40 micrograms/kg BIM 22015 increases rate of development of tetanic tension and amplitude of contraction of indirectly stimulated EDL. In a 21-day study, reinnervated BIM 22015-treated muscles retain tetanic strength, whereas ACTH/MSH(4-10)-treated muscles are significantly weakened. Both peptides show neurotrophic characteristics in their stimulation of endplate nerve terminal branching. However, in contrast to ACTH/MSH(4-10), BIM 22015 also prevents denervation atrophy of the EDL. This dual neurotrophic and myotrophic role for BIM 22015 accords it a clinical potential for degenerative myopathies of either pure or mixed origin, such as muscular dystrophy, infantile spinal atrophy, and hypotonia.

Enhancement of motor nerve regeneration by nerve growth factor

The sciatic nerves of adult Wistar rats were severed bilaterally. Each nerve was sutured into a silicone tube used as a conduit, leaving a 5 mm gap in length between the nerve ends. Nerve growth factor in a saline solution vehicle was injected into the silicone chamber on the right side and normal saline solution (control) on the left. Six weeks after surgery, electrophysiological studies were performed. The motor nerve conduction velocities (MNCV) were significantly increased in the NGF-treated nerves. In one rat, the MNCV on the NGF-treated side was 66.6 m/s, in the range of normal nerves. There was no significant difference between the two sides in the amplitudes of evoked muscle action potentials. There are apparently no reports on the effect of NGF on motor neuron regeneration in vitro. In this study, NGF was found to enhance motor nerve regeneration.

Gangliosides: the relevance of current research to neurosurgery

Gangliosides are complex glycolipids found on the outer surface of most cell membranes: they are particularly concentrated in tissues of the nervous system. Gangliosides form part of the immunological identity of mammalian cells and are involved in a variety of cell-surface phenomena such as cell-substrate binding and receptor functions. In tumorous tissue, the ganglioside composition is altered, sometimes in direct proportion to the degree of malignancy. The literature on the glycosphingolipid composition and immunology of intracranial tumors is reviewed. Some gangliosides induce neuritogenesis and exhibit a trophic effect on nerve cells grown in vitro. In vivo, a particular ganglioside, GM1, reduces cerebral edema and accelerates recovery from injury (traumatic and ischemic) to the peripheral and central nervous systems of laboratory animals. Preliminary clinical studies have shown that treatment with gangliosides may have corresponding effects on lesions of the human peripheral nervous system. Gangliosides have not been tested in human subjects with brain injury.

Quantitative clinical electrophysiology in the evaluation of nerve injury and regeneration

Neuromuscular electrophysiological techniques can provide clinically important information about the localization, severity, and pathophysiology of peripheral nerve injuries, and about the progress of reinnervation. The relevant variables for study are compound nerve and muscle action potentials, motor unit action potentials, and denervation potentials. Available methods do not permit meaningful quantitation of regeneration. Newer methods under development attempt to estimate the number of motor units in a muscle and the number of axons in a nerve.

Critical review of gangliosides and thyrotropin-releasing hormone in peripheral neuromuscular diseases

The lack of effective therapy for many of the chronic neuromuscular diseases such as amyotrophic lateral sclerosis, hereditary motor sensory neuropathy (Charcot-Marie-Tooth disease), spinocerebellar degenerations and idiopathic polyneuropathy has led to a search for substances that may stimulate peripheral nerve regeneration. Two such agents that have been proposed are gangliosides (mixed purified bovine brain gangliosides, Cronassial) and thyrotropin releasing factor (TRH). Studies on both of these agents were initially reported with enthusiasm to be successful, but later double-blind controlled studies have failed to confirm these findings. This review provides critical analysis of the designs of studies of potentially effective agents in chronic neuromuscular diseases, and emphasizes the power of the placebo response, and the importance of designing placebos which are indistinguishable from the trial medication other than in the active effect.

Enhancement of peripheral nerve regeneration

Numerous factors external to the nerve cell can support and enhance nerve regeneration after injury. The definition of these factors and the elucidation of their mechanisms of action are the central goals of much contemporary neurobiologic research. This research will hopefully lead to the discovery of factors that will prove to be therapeutically beneficial for patients with either peripheral nervous system (PNS) injury or central nervous system (CNS) injury. This article reviews the biology of the regeneration response of the nerve to injury and discusses many of the factors that enhance nerve growth. Finally, the nerve guide or nerve regeneration chamber model for the evaluation of putative nerve regeneration enhancing agents in vivo is also discussed.