Effect of basic fibroblast growth factor and alpha-melanocytic stimulating hormone on nerve regeneration through a collagen channel

Appropriate dosage, timing, and site of intramuscular injections of brain-derived neurotrophic factor (BDNF) promote motor recovery after facial nerve injury in rats

INTRODUCTION/AIMS

Daily intramuscular injections of fibroblast growth factor 2 (FGF2) but not of brain-derived neurotrophic factor (BDNF) significantly improve whisking behavior and mono-innervation of the rat levator labii superioris (LLS) muscle 56 days after buccal nerve transection and suture (buccal-buccal anastomosis, BBA). We explored the dose-response of BDNF, FGF2, and insulin growth factor 2 (IGF2) on the same parameters, asking whether higher doses of BDNF would promote recovery.

METHODS

After BBA, growth factors were injected (30 μL volume) daily into the LLS muscle over 14, 28, or 56 days. At 56 days, video-based motion analysis of vibrissal whisking was performed and the extent of mono- and poly-reinnervation of the reinnervated neuromuscular junctions (NMJs) of the muscle determined with immunostaining of the nerve with β-tubulin and histochemical staining of the endplates with Alexa Fluor 488-conjugated α-bungarotoxin.

RESULTS

The dose-response curve demonstrated significantly higher whisking amplitudes and corresponding increased mono-innervation of the NMJ in the reinnervated LLS muscle at concentrations of 20-30 μg/mL BDNF administered daily for 14-28 days after BBA surgery. In contrast, high doses of IGF2 and FGF2, or doses of 20 and 40 μg/mL of BDNF administered for 14-56 days had no effect on either whisking behavior or in reducing poly-reinnervation of endplates in the muscle.

DISCUSSION

These data suggest that the re-establishment of mono-innervation of whiskerpad muscles and the improved motor function by injections of BDNF into the paralyzed vibrissal musculature after facial nerve injury have translation potential and promote clinical application.

Antifibrotic and Anti-Inflammatory Actions of α-Melanocytic Hormone: New Roles for an Old Player

The melanocortin system encompasses melanocortin peptides, five receptors, and two endogenous antagonists. Besides pigmentary effects generated by α-Melanocytic Hormone (α-MSH), new physiologic roles in sexual activity, exocrine secretion, energy homeostasis, as well as immunomodulatory actions, exerted by melanocortins, have been described recently. Among the most common and burdensome consequences of chronic inflammation is the development of fibrosis. Depending on the regenerative capacity of the affected tissue and the quality of the inflammatory response, the outcome is not always perfect, with the development of some fibrosis. Despite the heterogeneous etiology and clinical presentations, fibrosis in many pathological states follows the same path of activation or migration of fibroblasts, and the differentiation of fibroblasts to myofibroblasts, which produce collagen and α-SMA in fibrosing tissue. The melanocortin agonists might have favorable effects on the trajectories leading from tissue injury to inflammation, from inflammation to fibrosis, and from fibrosis to organ dysfunction. In this review we briefly summarized the data on structure, receptor signaling, and anti-inflammatory and anti-fibrotic properties of α-MSH and proposed that α-MSH analogues might be promising future therapeutic candidates for inflammatory and fibrotic diseases, regarding their favorable safety profile.

Putative roles of soluble trophic factors in facial nerve regeneration, target reinnervation, and recovery of vibrissal whisking

It is well-known that, after nerve transection and surgical repair, misdirected regrowth of regenerating motor axons may occur in three ways. The first way is that the axons enter into endoneurial tubes that they did not previously occupy, regenerate through incorrect fascicles and reinnervate muscles that they did not formerly supply. Consequently the activation of these muscles results in inappropriate movements. The second way is that, in contrast with the precise target-directed pathfinding by elongating motor nerves during embryonic development, several axons rather than a single axon grow out from each transected nerve fiber. The third way of misdirection occurs by the intramuscular terminal branching (sprouting) of each regenerating axon to culminate in some polyinnervation of neuromuscular junctions, i.e. reinnervation of junctions by more than a single axon. Presently, "fascicular" or "topographic specificity" cannot be achieved and hence target-directed nerve regeneration is, as yet, unattainable. Nonetheless, motor and sensory reinnervation of appropriate endoneurial tubes does occur and can be promoted by brief nerve electrical stimulation. This review considers the expression of neurotrophic factors in the neuromuscular system and how this expression can promote functional recovery, with emphasis on the whisking of vibrissae on the rat face in relationship to the expression of the factors. Evidence is reviewed for a role of neurotrophic factors as short-range diffusible sprouting stimuli in promoting complete functional recovery of vibrissal whisking in blind Sprague Dawley (SD)/RCS rats but not in SD rats with normal vision, after facial nerve transection and surgical repair. Briefly, a complicated time course of growth factor expression in the nerves and denervated muscles include (1) an early increase in FGF2 and IGF2, (2) reduced NGF between 2 and 14days after nerve transection and surgical repair, (3) a late rise in BDNF and (4) reduced IGF1 protein in the denervated muscles at 28days. These findings suggest that recovery of motor function after peripheral nerve injury is due, at least in part, to a complex regulation of nerve injury-associated neurotrophic factors and cytokines at the neuromuscular junctions of denervated muscles. In particular, the increase of FGF2 and concomittant decrease of NGF during the first week after facial nerve-nerve anastomosis in SD/RCS blind rats may prevent intramuscular axon sprouting and, in turn, reduce poly-innervation of the neuromuscular junction.

Comparison of trophic factors' expression between paralyzed and recovering muscles after facial nerve injury. A quantitative analysis in time course

After peripheral nerve injury, recovery of motor performance negatively correlates with the poly-innervation of neuromuscular junctions (NMJ) due to excessive sprouting of the terminal Schwann cells. Denervated muscles produce short-range diffusible sprouting stimuli, of which some are neurotrophic factors. Based on recent data that vibrissal whisking is restored perfectly during facial nerve regeneration in blind rats from the Sprague Dawley (SD)/RCS strain, we compared the expression of brain derived neurotrophic factor (BDNF), fibroblast growth factor-2 (FGF2), insulin growth factors 1 and 2 (IGF1, IGF2) and nerve growth factor (NGF) between SD/RCS and SD-rats with normal vision but poor recovery of whisking function after facial nerve injury. To establish which trophic factors might be responsible for proper NMJ-reinnervation, the transected facial nerve was surgically repaired (facial-facial anastomosis, FFA) for subsequent analysis of mRNA and proteins expressed in the levator labii superioris muscle. A complicated time course of expression included (1) a late rise in BDNF protein that followed earlier elevated gene expression, (2) an early increase in FGF2 and IGF2 protein after 2 days with sustained gene expression, (3) reduced IGF1 protein at 28 days coincident with decline of raised mRNA levels to baseline, and (4) reduced NGF protein between 2 and 14 days with maintained gene expression found in blind rats but not the rats with normal vision. These findings suggest that recovery of motor function after peripheral nerve injury is due, at least in part, to a complex regulation of lesion-associated neurotrophic factors and cytokines in denervated muscles. The increase of FGF-2 protein and concomittant decrease of NGF (with no significant changes in BDNF or IGF levels) during the first week following FFA in SD/RCS blind rats possibly prevents the distal branching of regenerating axons resulting in reduced poly-innervation of motor endplates.

Poor functional recovery and muscle polyinnervation after facial nerve injury in fibroblast growth factor-2-/- mice can be improved by manual stimulation of denervated vibrissal muscles

Functional recovery following facial nerve injury is poor. Adjacent neuromuscular junctions (NMJs) are "bridged" by terminal Schwann cells and numerous regenerating axonal sprouts. We have recently shown that manual stimulation (MS) restores whisking function and reduces polyinnervation of NMJs. Furthermore, MS requires both insulin-like growth factor-1 (IGF-1) and brain-derived neurotrophic factor (BDNF). Here, we investigated whether fibroblast growth factor-2 (FGF-2) was also required for the beneficial effects of MS. Following transection and suture of the facial nerve (facial-facial anastomisis, FFA) in homozygous mice lacking FGF-2 (FGF-2(-/-)), vibrissal motor performance and the percentage of poly-innervated NMJ were quantified. In intact FGF-2(-/-) mice and their wildtype (WT) counterparts, there were no differences in amplitude of vibrissal whisking (about 50°) or in the percentage of polyinnervated NMJ (0%). After 2 months FFA and handling alone (i.e. no MS), the amplitude of vibrissal whisking in WT-mice decreased to 22±3°. In the FGF-2(-/-) mice, the amplitude was reduced further to 15±4°, that is, function was significantly poorer. Functional deficits were mirrored by increased polyinnervation of NMJ in WT mice (40.33±2.16%) with polyinnervation being increased further in FGF-2(-/-) mice (50.33±4.33%). However, regardless of the genotype, MS increased vibrissal whisking amplitude (WT: 33.9°±7.7; FGF-2(-/-): 33.4°±8.1) and concomitantly reduced polyinnervation (WT: 33.9%±7.7; FGF-2(-/-): 33.4%±8.1) to a similar extent. We conclude that, whereas lack of FGF-2 leads to poor functional recovery and target reinnervation, MS can nevertheless confer some functional benefit in its absence.

Transplantation of olfactory ensheathing cells promotes axonal regeneration and functional recovery of peripheral nerve lesion in rats

INTRODUCTION

Olfactory ensheathing cells (OECs) hold promise for cell therapy because they may promote regeneration of the central nervous system. However, OECs have been less studied after peripheral nerve injury (PNI). The purpose of this investigation was to determine the effect of OEC transplantation on a severe sciatic nerve (SN) lesion.

METHODS

OECs were injected in rats after section and 2-cm resection of the SN.

RESULTS

Three months after therapy, muscle strength and morphometric studies showed complete restoration of the contractile properties of the gastrocnemius and complete repair of the SN. Immunohistochemistry and RT-PCR studies indicated an increase in the presence of neurotrophic factors. Interestingly, tracking of green fluorescent protein (GFP)-positive OECs showed that no OECs were present in the SN.

DISCUSSION

Our results demonstrate that, after severe PNI, OECs have remarkable potential for nerve regeneration by creating a favorable microenvironment.

Electrospun micro- and nanofiber tubes for functional nervous regeneration in sciatic nerve transections

Background

Although many nerve prostheses have been proposed in recent years, in the case of consistent loss of nervous tissue peripheral nerve injury is still a traumatic pathology that may impair patient's movements by interrupting his motor-sensory pathways. In the last few decades tissue engineering has opened the door to new approaches;: however most of them make use of rigid channel guides that may cause cell loss due to the lack of physiological local stresses exerted over the nervous tissue during patient's movement. Electrospinning technique makes it possible to spin microfiber and nanofiber flexible tubular scaffolds composed of a number of natural and synthetic components, showing high porosity and remarkable surface/volume ratio.

Results

In this study we used electrospun tubes made of biodegradable polymers (a blend of PLGA/PCL) to regenerate a 10-mm nerve gap in a rat sciatic nerve in vivo. Experimental groups comprise lesioned animals (control group) and lesioned animals subjected to guide conduits implantated at the severed nerve stumps, where the tubular scaffolds are filled with saline solution. Four months after surgery, sciatic nerves failed to reconnect the two stumps of transected nerves in the control animal group. In most of the treated animals the electrospun tubes induced nervous regeneration and functional reconnection of the two severed sciatic nerve tracts. Myelination and collagen IV deposition have been detected in concurrence with regenerated fibers. No significant inflammatory response has been found. Neural tracers revealed the re-establishment of functional neuronal connections and evoked potential results showed the reinnervation of the target muscles in the majority of the treated animals.

Conclusion

Corroborating previous works, this study indicates that electrospun tubes, with no additional biological coating or drug loading treatment, are promising scaffolds for functional nervous regeneration. They can be knitted in meshes and various frames depending on the cytoarchitecture of the tissue to be regenerated. The versatility of this technique gives room for further scaffold improvements, like tuning the mechanical properties of the tubular structure or providing biomimetic functionalization. Moreover, these guidance conduits can be loaded with various fillers like collagen, fibrin, or self-assembling peptide gels or loaded with neurotrophic factors and seeded with cells. Electrospun scaffolds can also be synthesized in different micro-architectures to regenerate lesions in other tissues like skin and bone.

US Food and Drug Administration/Conformit Europe-approved absorbable nerve conduits for clinical repair of peripheral and cranial nerves

Several absorbable nerve conduits are approved by the US Food and Drug Administration (FDA) and Conformit Europe (CE) for clinical repair of peripheral and cranial nerves. Surgeons are often not aware of the different (bio)materials of these conduits when performing nerve repair. An overview of these FDA- and CE-approved absorbable nerve conduits for clinical use is presented. PubMed, MEDLINE, and the companies selling the conduits were consulted. The available FDA and CE absorbable nerve conduits for peripheral and cranial nerve repair are 2 collagen- and 2 synthetic-polyester-based conduits. The available clinical data, the price, the length, and the composition of the tube show significant differences. Based on the available data in this paper at this moment, we favor the PGA (Neurotube) nerve conduit for repair of peripheral and cranial nerve defects because of its advantages in length, price, and availability of clinical data. However, no prospective studies comparing the available nerve conduits have been published.

Absorbable collagen sponge combined with recombinant human basic fibroblast growth factor promotes nerve regeneration in rat sciatic nerve

Recombinant human basic fibroblast growth factor (rhbFGF) is a peptide with many bioactivities such as promoting proliferation and migration of various cells. It plays an important role in neuroprotection and enhancement of nerve regeneration. Due to its short half-life in the body, local administration by injection is limited. To prolong the bioactivity of rhbFGF and to enhance its biological effects, absorbable collagen sponge was used as matrixes and carriers for controlled release of rhbFGF. The effects of rhbFGF soaked into an absorbable collagen sponge (rhbFGF/ACS) for the repair of rat sciatic nerve injury were evaluated. The functional, electrophysiological and histological examinations demonstrate the treatment with rhbFGF/ACS can enhance rat sciatic nerve repair, and its effectiveness is better than free rhbFGF alone. It is concluded the rhbFGF/ACS is a promising biomaterial to improve the repair and regeneration of sciatic nerve injury.

Incorporation of basic fibroblast growth factor by a layer-by-layer assembly technique to produce bioactive substrates

Basic fibroblast growth factor (bFGF) was immobilized onto quartz slides and collagen films by assembly with chondroitin sulfate (CS) in a layer-by-layer (LBL) manner. First, the LBL-deposition process on the amino-silanized quartz slides was monitored by UV-vis spectroscopy and water contact angle measurement. By substituting the normal bFGF with rhodamine-labeled one (Rd-bFGF), a linear increase of the absorbance versus bilayer number was recorded. The water contact angle oscillated between the odd CS and the even bFGF layers, demonstrating the alternating change of the surface chemistry. Scanning force microscopy (SFM) revealed that the surface topography was altered slightly after multilayer assembly. In vitro incubation of the CS/bFGF multilayers in PBS showed that approximately 30% of the incorporated bFGF was released within 8 days. In vitro cell culture found that the fibroblasts showed star-like morphology with plenty of pseudopods on the bFGF-incorporated collagen film after cultured for 1 day, and the collagen films assembled with bFGF possess improved bioactivity than that of the virgin one and the bFGF control. Since the immobilized growth factors can maximally retain their bioactivity, the LBL assembly would be a potential approach to construct a bioactive substrate for biomedical applications.

Enhanced angiogenesis through controlled release of basic fibroblast growth factor from peptide amphiphile for tissue regeneration

In the present study, we hypothesized that a novel approach to promote vascularization would be to create injectable three-dimensional (3-D) scaffolds with encapsulated growth factor that enhance the sustained release of growth factor and induce the angiogenesis. We demonstrate that a 3-D scaffold can be formed by mixing of peptide-amphiphile (PA) aqueous solution with basic fibroblast growth factor (bFGF) suspension. PA was synthesized by standard solid phase chemistry that ends with the alkylation of the NH(2) terminus of the peptide. A 3-D network of nanofibers was formed by mixing bFGF suspensions with dilute aqueous solutions of PA. Scanning electron microscopy (SEM) observation revealed the formation of fibrous assemblies with an extremely high aspect ratio and high surface areas. In vitro and in vivo release profile of bFGF from 3-D network of nanofibers was investigated while angiogenesis induced by the released bFGF was assessed. When aqueous solution of PA was subcutaneously injected together with bFGF suspension into the back of mice, a transparent 3-D hydrogel was formed at the injected site and induced significant angiogenesis around the injected site, in marked contrast to bFGF injection alone or PA injection alone. The combination of bFGF-induced angiogenesis is a promising procedure to improve tissue regeneration.

The wrapping method using biodegradable felt strips has a preventive effect on the thinning of the aortic wall: Experimental study in the canine aorta

OBJECTIVES

Wrapping methods have been widely used to reinforce the anastomotic site in vascular surgery; however, postoperative changes in the aortic wall wrapped by nonbiodegradable felt have not been well characterized. The purposes of this investigation are to elucidate the sequelae of wrapping with nonbiodegradable felt on the aortic wall and to modify those changes by using biodegradable felt with or without basic fibroblast growth factor (bFGF).

METHODS

The descending thoracic aortas of 15 beagles were wrapped with three different materials: nonbiodegradable polytetrafluoroethylene (PTFE) felt, biodegradable polyglycol acid (PGA) material, and PGA with 100 microg bFGF (n = 5 in each group). The descending thoracic aorta was resected after 3 months. The thickness of the aortic wall, vessel density in the media and the adventitia, and the wall strength were assessed. Untreated native aortic wall served as a normal control.

RESULTS

The thickness of the media of the PTFE group was lower than that of the PGA + bFGF group (66% +/- 5% vs 85% +/- 6% of control, P < .05). The adventitia-media ratio in the PTFE group decreased compared with controls (59.1% of normal, P < 0.05), whereas those in the PGA and PGA + bFGF groups increased (172.1% and 189.6% of normal, respectively, P < .01). The collagen-smooth muscle ratio in the media was higher in the PTFE group than in the controls (0.14 +/- 0.02 vs 0.07 +/- 0.01, P < .01). The number of vessels in the adventitia was higher in the PGA + bFGF group than those in PTFE or PGA groups (29.6 +/- 2.5/mm2 vs 6.4 +/- 0.8/mm2, 19.0 +/- 1.1/mm2, P < .01). The PGA + bFGF group demonstrated larger failure force than the PTFE group (4.0 +/- 0.3 kgf vs 1.6 +/- 0.3 kgf, P < .01). The failure stress in the PGA and PGA + bFGF groups was larger than that in PTFE group (PTFE:PGA + bFGF = 5.3 +/- 0.9 x10(2) kPa:11.7 +/- 1.7 x 10(2) kPa, P < .01; PTFE:PGA = 5.3 +/- 0.9 x 10(2) kPa:11.2 +/- 1.2 x 10(2) kPa, P < .05).

CONCLUSION

The aortic wall wrapped with nonbiodegradable PTFE felt showed a reduced thickness and diminished vessels in the adventitia. Biodegradable felt (PGA), with or without bFGF, modified these histologic changes. The vessel-rich thickened adventitia, after wrapping by PGA with bFGF, was associated with increased aortic wall strength.

CLINICAL RELEVANCE

This investigation was conducted in an attempt to elucidate mechanisms underlying the occurrence of late postoperative false aneurysm after aortic surgery. We hypothesized that sustaining compression of the aorta by the felt strip may cause structural derangement and local ischemia on the aortic wall. We used a simple wrapping of the aorta with a felt strip rather than a felt strip at anastomotic sites to simplify the experimental model and to exclude confounding factors brought by technical inconsistency on the surgical anastomosis. We further attempted to find a clue for preventing adverse effects of wrapping with a conventional felt strip. Practically, we pursued a possible application of a biodegradable felt strip to aortic wrapping in our experimental model before we proceed in a clinical application of the new material.

Development of fibrous biodegradable polymer conduits for guided nerve regeneration

The technique of microbraiding with modification was employed as a novel method for the fabrication of fibrous tubular scaffolds for nerve tissue engineering purposes. The biodegradable polymers used in this study were poly(L-lactide-co-glycolide) (10:90) and chitosan. The polymeric fibers were microbraided around a Teflon mandrel to make it as a tubular construct. The conduits were then studied for their surface morphology, swelling behaviour and biocompatibility. The surface morphology was analysed by scanning electron microscope, swelling behaviour by weight increase due to water uptake and biocompatibility by in vitro cytotoxicity assessment in terms of cell morphology and cell viability by the MTT assay of polymer extract treated cells. These conduits may also be used for regeneration of tissues, which require tubular scaffolds such as blood vessel, spinal cord, intestine etc.

Effect of genetically modified Schwann cells with increased motility in end-to-side nerve grafting

Taking into account that Schwann-cell (SC) motility is a prerequisite for myelination during peripheral nerve regeneration, the present study was designed with the intention to increase SC motility in vitro and to evaluate the effect of transduced SC on nerve regeneration in vivo, through silicone tubes after end-to-side nerve repair. Our in vitro study demonstrated that SC transduction with the pREV-HW3 retrovirus, encoding for sialyl-transferase-X (STX), significantly increased their motility compared to the control. In the in vivo study, 45 Wistar rats were randomized into three groups of 15 each. In all animals, the left peroneal nerve was severed, and a 10-mm segment was removed. The distal stump of the peroneal nerve was connected end-to-side to a perineurial window in the ipsilateral tibial nerve with either a silicone tube lined with SC (group A) or a silicone tube lined with STX-transduced SC (groups B and C). Fluorescence and light microscopy in group C showed that SCs were viable the first critical 15 postoperative days. After 90 days, light microscopy in group B demonstrated that STX-transduced SCs with increased motility ensured nerve regeneration, through silicone tubes, in all cases. Furthermore, STX-transduced SCs increased significantly fiber diameter and myelin thickness, and most importantly enhanced significantly the functional outcome compared to non-transduced SCs.

Peripheral nerve regeneration by microbraided poly(L-lactide-co-glycolide) biodegradable polymer fibers

Tiny tubes with fiber architecture were developed by a novel method of fabrication upon introducing some modification to the microbraiding technique, to function as nerve guide conduit and the feasibility of in vivo nerve regeneration was investigated through several of these conduits. Poly(L-lactide-co-glycolide) (10:90) polymer fibers being biocompatible and biodegradable were used for the fabrication of the conduits. The microbraided nerve guide conduits (MNGCs) were characterized using scanning electron microscopy to study the surface morphology and fiber arrangement. Degradation tests were performed and the micrographs of the conduit showed that the degradation of the conduit is by fiber breakage indicating bulk hydrolysis of the polymer. Biological performances of the conduits were examined in the rat sciatic nerve model with a 12-mm gap. After implantation of the MNGC to the right sciatic nerve of the rat, there was no inflammatory response. One week after implantation, a thin tissue capsule was formed on the outer surface of the conduit, indicating good biological response of the conduit. Fibrin matrix cable formation was seen inside the MNGC after 1 week implantation. One month after implantation, 9 of 10 rats showed successful nerve regeneration. None of the implanted tubes showed tube breakage. The MNGCs were flexible, permeable, and showed no swelling apart from its other advantages. Thus, these new poly(L-lactide-co-glycolide) microbraided conduits can be effective aids for nerve regeneration and repair and may lead to clinical applications.

Targeting Melanocortin Receptors as a Novel Strategy to Control Inflammation

Adrenocorticotropic hormone and alpha-, beta-, and gamma-melanocyte-stimulating hormones, collectively called melanocortin peptides, exert multiple effects upon the host. These effects range from modulation of fever and inflammation to control of food intake, autonomic functions, and exocrine secretions. Recognition and cloning of five melanocortin receptors (MCRs) has greatly improved understanding of peptide-target cell interactions. Preclinical investigations indicate that activation of certain MCR subtypes, primarily MC1R and MC3R, could be a novel strategy to control inflammatory disorders. As a consequence of reduced translocation of the nuclear factor kappaB to the nucleus, MCR activation causes a collective reduction of the major molecules involved in the inflammatory process. Therefore, anti-inflammatory influences are broad and are not restricted to a specific mediator. Short half-life and lack of selectivity could be an obstacle to the use of the natural melanocortins. However, design and synthesis of new MCR ligands with selective chemical properties are already in progress. This review examines how marshaling MCR could control inflammation.

Beneficial effect of nerve growth factor-7S on peripheral nerve regeneration through inside-out vein grafts: An experimental study

This study investigated the effect of local administration of nerve growth factor-7S (NGF-7S) on the axonal regrowth of mixed peripheral nerves through inside-out vein grafts. Sixty male Wistar rats were randomized into two groups (n = 30). A defect 12 mm long in the right sciatic nerve was created and repaired with an inside-out vein graft from the right jugular vein. NGF-7S (group A) or phosphate-buffered saline (group B; control) was locally administered daily during the first 3 weeks. Walking-track analysis and electrophysiological and histological-morphometric studies were carried out 4, 6, 8, 10, and 12 weeks postoperatively (subgroups a, b, c, d, and e, respectively, n = 6 each). Data analysis showed that 1) the recovery of motor function, as measured by walk pattern analysis and evoked muscle action potential, and 2) the orientation, number, myelin thickness, and diameter of myelinated fibers were better in the NGF-7S than in the control group. These findings present strong evidence of the beneficial effect of NGF-7S on peripheral nerve regeneration through inside-out vein grafts.

Peripheral nerve regeneration with sustained release of poly(phosphoester) microencapsulated nerve growth factor within nerve guide conduits

Prolonged delivery of neurotrophic proteins to the target tissue is valuable in the treatment of various disorders of the nervous system. We have tested in this study whether sustained release of nerve growth factor (NGF) within nerve guide conduits (NGCs), a device used to repair injured nerves, would augment peripheral nerve regeneration. NGF-containing polymeric microspheres fabricated from a biodegradable poly(phosphoester) (PPE) polymer were loaded into silicone or PPE conduits to provide for prolonged, site-specific delivery of NGF. The conduits were used to bridge a 10 mm gap in a rat sciatic nerve model. Three months after implantation, morphological analysis revealed higher values of fiber diameter, fiber population and fiber density and lower G-ratio at the distal end of regenerated nerve cables collected from NGF microsphere-loaded silicone conduits, as compared with those from control conduits loaded with either saline alone, BSA microspheres, or NGF protein without microencapsulation. Beneficial effects on fiber diameter, G-ratio and fiber density were also observed in the permeable PPE NGCs. Thus, the results confirm a long-term promoting effect of exogenous NGF on morphological regeneration of peripheral nerves. The tissue-engineering approach reported in this study of incorporation of a microsphere protein release system into NGCs holds potential for improved functional recovery in patients whose injured nerves are reconstructed by entubulation.

The effects of electroacupuncture on peripheral nerve regeneration in rats

This study was designed to examine the effects of electroacupuncture with direct current (DC) on peripheral nerve regeneration. The left sciatic nerve of 55 7-month-old rats was crushed at the thigh. They were ramdomly allocated to four groups: distal cathode DC group (n = 15), distal anode DC group (n = 14), sham operated group (n = 13), and control group (n = 13). In the distal cathode DC group, a cathode electrode was connected to an insulated acupuncture needle inserted at 1 cm distal to the injured site, while an anode electrode was connected to a needle inserted at 1 cm proximal to the lesion. In the distal anode DC group, the anode and the cathode electrode were connected to the needle at 1 cm distal and proximal to the lesion respectively. In the sham operated group, no electrical stimulation was given to the insulated needle inserted at the same site, and in the control group, no treatment was given. Regeneration of the sciatic nerve was evaluated by the number of evoked EMGs recorded at 12 sites in the plantar region, by their latency, and by the weight ratio of the tibialis anterior at four weeks after the crush injury. Regeneration of the peripheral nerve was faster and more accelerated in the distal cathode DC group than in the other groups, while in the distal anode DC group the regeneration was delayed. This result suggested electroacupuncture with cathode distal orientation might be a useful treatment having the advantage of enabling deeper insertion with minimal tissue damage.

Rat Schwann cells in bioresorbable nerve guides to promote and accelerate axonal regeneration

A micro-structured, biodegradable, semipermeable hollow nerve guide implant was developed to bridge nerve lesions. Quantitative comparison of cell migration and axonal growth using time lapse video recording in vitro revealed that axons grow eight times faster than neuritotrophic Schwann cells migrate. To accelerate regeneration, purified Schwann cells are best injected into nerve guides before implantation. Nerve guides made from resorbable poly-lactide-co-glycolide support Schwann cell attachment, cell survival, and axonal outgrowth in vitro. The therapeutic concept aims at the development of an 'intelligent neuroprosthesis' that first mediates regeneration and then disappears.

Transplantation of olfactory mucosa minimizes axonal branching and promotes the recovery of vibrissae motor performance after facial nerve repair in rats

The occurrence of abnormally associated movements is inevitable after facial nerve transection. The reason for this post-paralytic syndrome is poor guidance of regrowing axons, whereby a given muscle group is reinnervated by misrouted axonal branches. Olfactory ensheathing glia have been shown to reduce axonal sprouting and stimulate axonal regeneration after transplantation into the spinal cord. In the present study, we asked whether transplantation of olfactory mucosa (OM) would also reduce sprouting of a damaged peripheral pure motor nerve. The adult facial nerve was transected, and the effect of the OM placed at the lesion site was analyzed with regard to the accuracy of target reinnervation, axonal sprouting of motoneurons, and vibrissal motor performance. Accuracy of target reinnervation and axonal sprouting were studied using preoperative/postoperative labeling and triple retrograde labeling of facial motoneurons, respectively. The vibrissal motor performance was monitored using a video-based motion analysis. We show here that implantation of OM, compared with simple facial-facial anastomosis, (1) improved the protraction, amplitude, angular velocity, and acceleration of vibrissal movements up to 80% of the control values, (2) reduced the percentage of branching motoneurons from 76 to 39%, and (3) improved the accuracy of reinnervation from 22 to 49%. Moreover, we present evidence, that transplanted OM but not buccal mucous membrane induced a sustained upregulation of trophic factors at the lesion site. It is concluded that transplantation of OM to the transected facial nerve significantly improves nerve regeneration.

Focal application of neutralizing antibodies to soluble neurotrophic factors reduces collateral axonal branching after peripheral nerve lesion

A major reason for the insufficient recovery of function after motor nerve injury are the numerous axonal branches which often re-innervate muscles with completely different functions. We hypothesized that a neutralization of diffusable neurotrophic factors at the lesion site in rats could reduce the branching of transected axons. Following analysis of local protein expression by immunocytochemistry and by in situ hybridization, we transected the facial nerve trunk of adult rats and inserted both ends into a silicon tube containing (i) collagen gel with neutralizing concentrations of antibodies to NGF, BDNF, bFGF, IGF-I, CNTF and GDNF; (ii) five-fold higher concentrations of the antibodies and (iii) combination of antibodies. Two months later, retrograde labelling was used to estimate the portion of motoneurons the axons of which had branched and projected into three major branches of the facial trunk. After control entubulation in collagen gel containing non-immune mouse IgG 85% of all motoneurons projecting along the zygomatic branch sprouted and sent at least one twin axon to the buccal and/or marginal-mandibular branches of the facial nerve. Neutralizing concentrations of anti-NGF, anti-BDNF and anti-IGF-I significantly reduced sprouting. The most pronounced effect was achieved after application of anti-BDNF, which reduced the portion of branched neurons to 18%. All effects after a single application of antibodies were concentration-dependent and superior to those observed after combined treatment. This first report on improved quality of reinnervation by antibody-therapy implies that, in rats, the post-transectional collateral axonal branching can be reduced without obvious harmful effects on neuronal survival and axonal elongation.

Axonal regeneration into Schwann cell grafts within resorbable poly(alpha-hydroxyacid) guidance channels in the adult rat spinal cord

Axonal growth and myelination in a SC graft contained in a resorbable tubular scaffold made of poly(D,L-lactic acid) (PLA50) or high molecular weight poly(L-lactic acid) mixed with 10% poly(L-lactic acid) oligomers (PLA(100/10)) were studied for up to 4 months after implantation in the completely transected adult rat thoracic spinal cord. The PLA50 tubes collapsed soon after implantation and, consequently, compressed the graft inside, leading to only occasional thin cables with SCs and a low number of myelinated axons: 17 +/- 6 at 1 and 158 +/- 11 at 2 months post-grafting. The cable contained 32 +/- 23 blood vessels at 2 weeks, 55 +/- 33 at 1 month and 46 +/- 30 at 2 months after implantation. PLA(100/10) tubes, on the other hand, were found to break up into large pieces, which compressed and sometimes protruded into the tissue cable inside. At all time points studied, however, cables contained SCs and were well vascularized with 414 +/- 47 blood vessels at 2 weeks, 437 +/- 139 at 1, 609 +/- 134 at 2 and 396 +/- 95 at 4 months post-grafting. The number of myelinated axons was 712 +/- 509 at 1 month, 1819 +/- 837 at 2 months and 609 +/- 132 at 4 months post implantation. These results demonstrated that fiber growth and myelination into a SC graft contained in a resorbable PLA(100/10) tube increases over the first 2 months post-implantation but decreases thereafter. Changes in geometry of both types of polymer tubes were detrimental to axonal regeneration. Future research should explore the use of polymers that better retain the appropriate mechanical, geometrical and permeability properties over time.

Reinnervation of a denervated skeletal muscle by spinal axons regenerating through a collagen channel directly implanted into the rat spinal cord

In the present study, the continuity between the central nervous system (CNS) and the peripheral nervous system (PNS) was restored by mean of a collagen channel in order to reinnervate a skeletal muscle. Three groups of animals were considered. In the first group, one end of the collagen channel was implanted in the cervical spinal cord of adult rats. The other end was connected to a 30-mm autologous peripheral nerve graft (PNG) implanted into the denervated biceps brachii muscle. The gap between the spinal cord and the proximal nerve stump varied from 3 to 7 mm. In the second group of animals, the distal end of the PNG graft was ligatured in order to compare the survival of the growing axons in the presence and in the absence of a muscular target. In the third group of animals, the extraspinal stump of the collagen channel was ligatured. Our study demonstrates that spinal neurons and dorsal root ganglion (DRG) neurons can grow long axons through the collagen channel over a 7-mm gap and reinnervate a denervated skeletal muscle. The results also indicate that the presence of a PNG at the extraspinal stump of the collagen channel is essential for axonal regrowth and that the muscle target contributes to the long-term maintenance of the regenerating axons. These data might be interesting for clinical application when the continuity between the CNS and PNS is interrupted such as in root avulsion.

Regrowth of the rostral spinal axons into the caudal ventral roots through a collagen tube implanted into hemisected adult rat spinal cord

OBJECTIVE

A collagen tube was used to guide axonal regrowth from the spinal cord to the periphery to contribute to improvement of paralysis after lower thoracic spinal cord injury.

METHODS

The spinal cords of adult male Sprague-Dawley rats were lesioned by removing the left hemicord from T12 to 5 mm below this level and additionally sectioning all left lumbar ventral roots. In experimental animals (n = 9), a collagen tube was inserted into this gap, spanning the rostral hemisected cord to the caudal sectioned lumbar ventral roots (gap, 7 mm). In control animals (n = 6), no treatment was performed.

RESULTS

Six months after surgery, the return of some tension and resistance of the paralyzed hindlimb muscles was observed in all experimental rats except the untreated controls. Nine months postoperatively, muscle action potentials were recorded from the target muscles of the experimental animals while electrostimulating the tissue continuity within the collagen tube. Horseradish peroxidase retrograde labeling showed that the neurons in the rostral cord near the implantation site regrew into the reconnected lumbar ventral roots. Histological examination indicated numerous myelinated axons in the reconnected root pathways and newly formed endplates in the target muscles. No axonal regeneration was found in the control rats.

CONCLUSION

These results indicate that the rostral spinal axons can regrow into the caudal sectioned and reconnected ventral roots through a collagen tube, thus innervating the denervated peripheral targets in adult rats after spinal cord injury. This surgical repair model also provides a means for testing the use of trophic factors that may further promote axonal regeneration.

Influence of gelatin complexation on cell proliferation activity and proteolytic resistance of basic fibroblast growth factor

The objective of this study is to investigate the influence of gelatin complexation on the biological activity of basic fibroblast growth factor (bFGF) and its resistance to trypsin digestion. When bFGF was mixed at 37 degrees C with acidic gelatin with an isoelectric point (IEP) of 5.0, the activity to promote in vitro proliferation of BHK cells became lower compared with that of free bFGF, in contrast to mixing with the basic gelatin with an IEP of 9.0. A maximum reduction in the bFGF activity was observed for the bFGF-gelatin complex prepared at a mixing molar ratio of 1/1. The bFGF activity of cell proliferation reduced at the initial period after mixing with the acidic gelatin at 37 degrees C, followed by no substantial change. Complexation with the acidic gelatin at 4 degrees C had no influence on the bFGF activity, irrespective of the bFGF/gelatin ratio and complexation time. The biological activity of bFGF was reduced by the trypsin treatment, but the reduced extent was suppressed through gelatin complexation at 37 degrees C. In an electrophoresis study, the protective effect of gelatin complexation on the trypsin digestion was also confirmed in terms of the molecular weight loss. It is possible that the complexing gelatin covers bFGF molecules, resulting in suppression of their interaction with the cell surface receptor as well as protection from their enzymatic attack.

The importance of drug delivery systems in tissue engineering

Tissue engineering is designed to regenerate natural tissues or to create biological substitutes for defective or lost tissues and organs through the use of cells. In addition to cells and their scaffolds, growth factors are required to promote tissue regeneration. Indeed, growth factor-induced vascularization is effective in supplying the oxygen and nutrients necessary for the survival of transplanted cells in organ substitution. However, growth factors have poor in vivo stability and so the biological effects are often unpredictable unless the delivery system is contrived. This review provides several examples to emphasize the importance of drug delivery systems in tissue engineering.

Biohybride nerve guide for regeneration: degradable polylactide fibers coated with rat Schwann cells

The restricted capacity of the nervous system to regenerate calls for novel therapeutic concepts. We have tested biocompatible polylactide fibers as potential nerve guides that could bridge proximal nerve stumps and synaptic target regions after nerve lesion. Polylactides have the great advantage that they degrade and resorb after completion of regeneration. Material surface properties were optimized three-fold by oxygen plasma treatment, polyanion coating and the seeding of Schwann cells from rat sciatic nerve. Immunocytochemistry and scanning electron microscopy revealed that in vitro axonal outgrowth of dorsal root ganglia on two specifically synthesized lactide polymers can be greatly improved by these surface treatments. The approach aims to develop an 'intelligent neuroprosthesis' that in vivo facilitates directed axonal regrowth in the first place and disappears thereafter.

Vascularization effect of basic fibroblast growth factor released from gelatin hydrogels with different biodegradabilities

Biodegradable gelatin hydrogels were prepared through the glutaraldehyde crosslinking of acidic gelatin with an isoelectric point (IEP) of 5.0 and the basic gelatin with an IEP of 9.0. The hydrogel water content was changed by the concentration of both gelatin and glutaraldehyde, used for hydrogel preparation. An aqueous solution of basic fibroblast growth factor (bFGF) was sorbed into the gelatin hydrogel freeze-dried to obtain a bFGF-incorporating gelatin hydrogel. Irrespective of the hydrogel water content, approximately 30% of the incorporated bFGF was released from the bFGF-incorporating acidic gelatin hydrogel, within the first day into phosphate-buffered saline solution at 37 degrees C, followed by no substantial release. Probably, the basic bFGF complexed with the acidic gelatin through poly-ion complexation would not be released under the in vitro non-degradation condition of gelatin. On the contrary, almost 100% of the incorporated bFGF was initially released from all types of basic gelatin hydrogels. This is due to the simple diffusion of bFGF because of no complexation between bFGF and the basic gelatin. When implanted subcutaneously into the mouse back, bFGF-incorporating acidic and basic gelatin hydrogels with higher water contents were degraded with time faster than those with lower water contents. Significant neovascularization was induced around the implanted site of the bFGF-incorporating acidic gelatin hydrogel. The induction period prolonged with the decrease in hydrogel water content. On the other hand, such a prolonged vascularization effect was not achieved by the bFGF-incorporating basic gelatin hydrogel and the hydrogel initially exhibited less enhanced effect, irrespective of the water content. These findings indicate that the controlled release of biologically active bFGF is caused by biodegradation of the acidic gelatin hydrogel, resulting in induction of vascularization effect dependent on the water content. It is possible that only the transient vascularization by the basic gelatin hydrogel is due to the initial large burst in bFGF release, probably because of the down regulation of bFGF receptor.

Biodegradation of hydrogel carrier incorporating fibroblast growth factor

In vivo release of basic fibroblast growth factor (bFGF) from a biodegradable gelatin hydrogel carrier was compared with the in vivo degradation of hydrogel. When gelatin hydrogels incorporating 125I-labeled bFGF were implanted into the back subcutis of mice, the bFGF radioactivity remaining decreased with time and the retention period was prolonged with a decrease in the water content of the hydrogels. The lower the water content of 125I-labeled gelatin hydrogels, the faster both the weight of the hydrogels and the gelatin radioactivity remaining decreased with time. The decrement profile of bFGF remaining in hydrogels was correlated with that of hydrogel weight and gelatin radioactivity, irrespective of the water content. Subcutaneous implantation of bFGF-incorporating gelatin hydrogels into the mice induced significant neovascularization. The retention period of neovascularization became longer as the water content of the hydrogels decreased. To study the decrease of activity of bFGF when implanted, bFGF-incorporating hydrogels were placed in diffusion chamber and implanted in the mouse subcutis for certain periods of time. When hydrogels explanted from the mice were again implanted, significant neovascularization was still observed, indicating that most of the biological activity of bFGF was retained in the hydrogels. It was concluded that, in our hydrogel system, biologically active bFGF was released as a result of in vivo degradation of the hydrogel. The release profile was controllable by changing the water content of hydrogels.

Neovascularization effect of biodegradable gelatin microspheres incorporating basic fibroblast growth factor

Biodegradable microspheres were prepared through glutaraldehyde cross-linking of gelatin without using any surfactants as a carrier matrix of basic fibroblast growth factor (bFGF). In the in vitro system, bFGF was sorbed to microspheres of acidic gelatin with an isoelectric point (IEP) of 5.0, but not to those of basic gelatin with an IEP of 9.0. The rate of bFGF sorption to the acidic gelatin microsphere in phosphate-buffered saline solution (pH 7.4) was smaller than that in water. Following incorporation of bFGF into the microspheres at 4 degrees C for 12 h, bFGF release from the bFGF-incorporating microspheres was studied. Approximately 30% of incorporated bFGF was released from the acidic gelatin microsphere within the initial 3 h, followed by no substantial release, whereas the basic gelatin microsphere released almost completely the incorporated bFGF within 1 day. It is likely that when basic bFGF molecules were immobilized to the acidic gelatin constituting microspheres through polyion complexation, they were not readily released under the in vitro nondegradation condition of gelatin. Incorporation of anionic carboxylmethyl cellulose (CMC) into the acidic gelatin microspheres reduced the amount of bFGF desorbed initially. This indicates that the initial burst is ascribed to free bFGF which is not ionically interacted with the acidic gelatin. CMC will function as a bFGF sorbent to suppress the initial leakage from the microspheres. When injected subcutaneously into the mouse back, bFGF-incorporating acidic gelatin microspheres were degraded over time and induced neovascularization around the injection site, in marked contrast to bFGF in the solution form. CMC incorporation slowed down the biodegradation and vascularization effect of bFGF-incorporating gelatin microspheres. It was concluded that the gelatin microsphere was a promising carrier matrix of bFGF to enhance the vascularization effect.

Complexation of basic fibroblast growth factor with gelatin

Polyion complexation between basic fibroblast growth factor (bFGF) and gelatin was studied by the turbidity change of mixed solution, heparin high performance liquid affinity chromatography (HPLAC), and isoelectric electrophoresis. When an aqueous solution of acidic gelatin with an isoelectric point (IEP) of 5.0 was mixed with that of bFGF, the turbidity of the mixed solution increased with time, whereas basic gelatin with and IEP of 9.0 did not cause any solution turbidity. A maximum turbidity of the mixed bFGF and acidic gelatin solution was observed around a bFGF/gelatin molar ratio of 1.0, irrespective of the gelatin concentration and solution temperature. The solution turbidity decreased with an increase in the ionic strength of the mixed solution. Complexation of bFGF with acidic gelatin was slower than that with poly(acrylic acid) probably because of the lower density of gelatin negative charge than that of poly(acrylic acid). HPLAC study revealed that complexation of bFGF with the acidic gelatin reduced the affinity of bFGF for heparin, in contrast to the basic gelatin, although the extent became smaller with the increasing ionic strength of the solution. An electrophoretic experiment showed that the IEP of bFGF shifted to a lower value after its gelatin complexation. These findings indicate that an electrostatic interaction is the main driving force for the complexation between acidic gelatin and basic bFGF.

The cellular and molecular basis of peripheral nerve regeneration

Functional recovery from peripheral nerve injury and repair depends on a multitude of factors, both intrinsic and extrinsic to neurons. Neuronal survival after axotomy is a prerequisite for regeneration and is facilitated by an array of trophic factors from multiple sources, including neurotrophins, neuropoietic cytokines, insulin-like growth factors (IGFs), and glial-cell-line-derived neurotrophic factors (GDNFs). Axotomized neurons must switch from a transmitting mode to a growth mode and express growth-associated proteins, such as GAP-43, tubulin, and actin, as well as an array of novel neuropeptides and cytokines, all of which have the potential to promote axonal regeneration. Axonal sprouts must reach the distal nerve stump at a time when its growth support is optimal. Schwann cells in the distal stump undergo proliferation and phenotypical changes to prepare the local environment to be favorable for axonal regeneration. Schwann cells play an indispensable role in promoting regeneration by increasing their synthesis of surface cell adhesion molecules (CAMs), such as N-CAM, Ng-CAM/L1, N-cadherin, and L2/HNK-1, by elaborating basement membrane that contains many extracellular matrix proteins, such as laminin, fibronectin, and tenascin, and by producing many neurotrophic factors and their receptors. However, the growth support provided by the distal nerve stump and the capacity of the axotomized neurons to regenerate axons may not be sustained indefinitely. Axonal regenerations may be facilitated by new strategies that enhance the growth potential of neurons and optimize the growth support of the distal nerve stump in combination with prompt nerve repair.

Peripheral nerve regeneration

Peripheral nerve regeneration comprises the formation of axonal sprouts, their outgrowth as regenerating axons and the reinnervation of original targets. This review focuses on the morphological features of axonal sprouts at the node of Ranvier and their subsequent outgrowth guided by Schwann cells or by Schwann cell basal laminae. Adhesion molecules such as N-CAM, L1 and N-cadherin are involved in the axon-to-axon and axon-to-Schwann cell attachment, and it is suggested that integrins such as alpha 1 beta 1 and alpha 6 beta 1 mediate the attachment between axons and Schwann cell basal laminae. The presence of synaptic vesicle-associated proteins such as synaptophysin, synaptotagmin and synapsin I in the growth cones of regenerating axons indicates the possibility that exocytotic fusion of vesicles with the surface axolemma supplies the membranous components for the extension of regenerating axons. Almost all the subtypes of protein kinase C have been localized in growth cones both in vivo and in vitro. Protein kinase C and GAP-43 are implicated to be involved in at least some part of the adhesion of growth cones to the substrate and their growth activity. The significance of tyrosine kinase in growth cones is emphasized. Tyrosine kinase plays an important role in intracellular signal transduction of the growth of regenerating axons mediated by both nerve trophic factors and adhesion molecules. Growth factors such as NGF, BDNF, CNTF and bFGF are also discussed mainly in terms of the influence of Schwann cells on regenerating axons.

Axonal regeneration

Axons damaged in a peripheral nerve are often able to regenerate from the site of injury along the degenerate distal segment of the nerve to reform functional synapses. Schwann cells play a central role in this process. However, in the adult mammalian central nervous system, from which Schwann cells are absent, axonal regeneration does not progress to allow functional recovery. This is due to inhibitors of axonal growth produced by both oligodendrocytes and astrocytes and also to the decreased ability of adult neurons to extend axons during regeneration compared to embryonic neurons during development. However once provided with a substrate conducive to axonal growth, such as a peripheral nerve graft, many central neurons are able to regenerate axons over long distances. Over the past year this response has been utilised in experimental models to produce a degree of behavioural recovery.

FGF inhibits neurite outgrowth over monolayers of astrocytes and fibroblasts expressing transfected cell adhesion molecules

We have cultured cerebellar neurons on monolayers of cortical astrocytes in control medium or medium containing recombinant basic fibroblast growth factor (FGF). FGF was found to inhibit neurite outgrowth, with a significant effect seen at 0.5 ng/ml and a maximal effect at 10 ng/ml. FGF increased the production of arachidonic acid (AA) in cerebellar neurons, and when added directly to cultures or generated endogenously via activation of phospholipase A2 using melittin, this second messenger could mimic the inhibitory effect of FGF. FGF and AA could also specifically inhibit neurite outgrowth stimulated by three cell adhesion molecules (NCAM, N-cadherin and L1) expressed in transfected fibroblasts, or in the case of L1 bound to a tissue culture substratum. These data demonstrate that, in certain cellular contexts, FGF can act as an inhibitory cue for axonal growth and that arachidonic acid is the second messenger responsible for this activity. We discuss the possibility that arachidonic acid inhibits neurite outgrowth by desensitising the second messenger pathway underlying neuronal responsiveness to cell adhesion molecules.