Effect of white adipose tissue flap and insulin-like growth factor-1 on nerve regeneration in rats

Biohacking Nerve Repair: Novel Biomaterials, Local Drug Delivery, Electrical Stimulation, and Allografts to Aid Surgical Repair

The regenerative capacity of the peripheral nervous system is limited, and peripheral nerve injuries often result in incomplete healing and poor outcomes even after repair. Transection injuries that induce a nerve gap necessitate microsurgical intervention; however, even the current gold standard of repair, autologous nerve graft, frequently results in poor functional recovery. Several interventions have been developed to augment the surgical repair of peripheral nerves, and the application of functional biomaterials, local delivery of bioactive substances, electrical stimulation, and allografts are among the most promising approaches to enhance innate healing across a nerve gap. Biocompatible polymers with optimized degradation rates, topographic features, and other functions provided by their composition have been incorporated into novel nerve conduits (NCs). Many of these allow for the delivery of drugs, neurotrophic factors, and whole cells locally to nerve repair sites, mitigating adverse effects that limit their systemic use. The electrical stimulation of repaired nerves in the perioperative period has shown benefits to healing and recovery in human trials, and novel biomaterials to enhance these effects show promise in preclinical models. The use of acellular nerve allografts (ANAs) circumvents the morbidity of donor nerve harvest necessitated by the use of autografts, and improvements in tissue-processing techniques may allow for more readily available and cost-effective options. Each of these interventions aid in neural regeneration after repair when applied independently, and their differing forms, benefits, and methods of application present ample opportunity for synergistic effects when applied in combination.

Adipose Tissue Uses in Peripheral Nerve Surgery

Currently, many different techniques exist for the surgical repair of peripheral nerves. The degree of injury dictates the repair and, depending on the defect or injury of the peripheral nerve, plastic surgeons can perform nerve repairs, grafts, and transfers. All the previously listed techniques are routinely performed in human patients, but a novel addition to these peripheral nerve surgeries involves concomitant fat grafting to the repair site at the time of surgery. Fat grafting provides adipose-derived stem cells to the injury site. Though fat grafting is performed as an adjunct to some peripheral nerve surgeries, there is no clear evidence as to which procedures have improved outcomes resultant from concomitant fat grafting. This review explores the evidence presented in various animal studies regarding outcomes of fat grafting at the time of various types of peripheral nerve surgery.

Autologous fat grafting for nerve regeneration and neuropathic pain: current state from bench-to-bedside

Despite recent advances in microsurgical techniques, functional recovery following peripheral nerve injury remains slow and inadequate. Poor peripheral nerve regeneration not only leaves patients with significant impairments, but also commonly leads to the development of debilitating neuropathic pain. Recent research has demonstrated the potential therapeutic benefits of adipose-derived stem cells, to enhance nerve regeneration. However, clinical translation remains limited due to the current regulatory burdens of the US FDA. A reliable and immediately translatable alternative is autologous fat grafting, where native adipose-derived stem cells present in the transferred tissue can potentially act upon regenerating axons. This review presents the scope of adipose tissue-based therapies to enhance outcomes following peripheral nerve injury, specifically focusing on their role in regeneration and ameliorating neuropathic pain.

State-of-the-Art Techniques in Treating Peripheral Nerve Injury

BACKGROUND

Peripheral nerve injuries remain a major clinical concern, as they often lead to chronic disability and significant health care expenditures. Despite advancements in microsurgical techniques to enhance nerve repair, biological approaches are needed to augment nerve regeneration and improve functional outcomes after injury.

METHODS

Presented herein is a review of the current literature on state-of-the-art techniques to enhance functional recovery for patients with nerve injury. Four categories are considered: (1) electroceuticals, (2) nerve guidance conduits, (3) fat grafting, and (4) optogenetics. Significant study results are highlighted, focusing on histologic and functional outcome measures.

RESULTS

This review documents the current state of the literature. Advancements in neuronal stimulation, tissue engineering, and cell-based therapies demonstrate promise with regard to augmenting nerve regeneration and appropriate rehabilitation.

CONCLUSIONS

The future of treating peripheral nerve injury will include multimodality use of electroconductive conduits, fat grafting, neuronal stimulation, and optogenetics. Further clinical investigation is needed to confirm the efficacy of these technologies on peripheral nerve recovery in humans, and how best to implement this treatment for a diverse population of nerve-injured patients.

Epineural adipose-derived stem cell injection in a sciatic rodent model

BACKGROUND

The aim was to evaluate the regenerative effect of epineural injection of rat ASCs (rASCs) in three different settings of acute and chronic compression in a rat sciatic nerve model.

METHODS

Acute compression (60 s) with a vessel clamp over a distance of 1 mm (group 1) or 10 mm (group 2), as well as chronic compression with a permanent remaining, nonabsorbable polymeric clip over a distance of 1 mm (group 3) was performed. Depending on the group, either 5 × 106 rASCs or the same volume (25 μl) of culture medium (CM) was injected with a 30G needle in the epineurium at the time of compression. Outcome measures were functional gait evaluations, imaging analysis, histomorphometric analyses, and muscle weight.

RESULTS

The rats in group 2 had a better function than those with group 1 at one and especially at 2 weeks. After 4 weeks however, almost all rats were close to a normal function. There was a similar Muscle Weight Ratio (MWR) after 2 weeks in all groups, whereas after 4 weeks, the MWR in group 3 was lower compared with group 1 and 2. Histomorphometric analysis showed a better myelination in group 1 & 2 compared to group 3 after 4 weeks. ASCs have a beneficial effect on myelin thickness (G-Ratio).

CONCLUSIONS

We successfully evaluated the regenerative effect of epineural injection of rASCs in three different settings of acute and chronic compression. However, there were no significant differences in outcomes between the ASC-treated groups and control groups.

Molecular Mechanism of the "Babysitter" Procedure for Nerve Regeneration and Muscle Preservation in Peripheral Nerve Repair in a Rat Model

OBJECTIVE

To investigate the molecular mechanism of nerve "babysitter" for nerve regeneration and muscle preservation in peripheral nerve repair.

METHODS

Eighty rats were equalized into 4 groups: peroneal nerve transected, group A received no treatment; group B underwent end-to-end repair; group C underwent end-to-side "babysitter" with donor epineurial window; group D underwent end-to-side "babysitter" with 40% donor neurectomy. During second-stage procedure, end-to-end neurorrhaphies were executed in groups A, C, and D. Expression of Insulin-like growth factor (IGF)-1 in spinal cord and IGF-1, TNF-like weak inducer of apoptosis (TWEAK), and Fn14 in anterior tibial muscles were evaluated by histopathology at 4-, 8-, 12-, and 24-week timepoints postoperatively.

RESULTS

At 4 weeks, group D expressed comparable IGF-1 with group B, and greater value than groups A and C in spinal cord. By 24 weeks, groups B and D showed higher values than groups A and C. Insulin-like growth factor 1 in muscles were greater in groups C and D than in groups A and B at 4 weeks, and comparable in all groups at 24 weeks. At 4 weeks, immunoreactive scores of TWEAK were 9.00 ± 0, 3.00 ± 0, 6.75 ± 0.75, and 6.75 ± 0.75, respectively. No differences were noticed in all groups by 24 weeks. At 4 weeks, Fn14 were similar in groups A, C, and D, but lower in group B. Group D showed comparable Fn14 with groups B and C, but lower value than group A at 24 weeks.

CONCLUSIONS

End-to-side nerve "babysitter" in peripheral nerve could promote fiber regeneration and muscle preservation by regulating expression of IGF-1 and TWEAK-Fn14. End-to-side "babysitter" with partial donor neurectomy could achieve comparable effects with end-to-end repair.

The potential roles for adipose tissue in peripheral nerve regeneration

INTRODUCTION

This review summarizes current understanding about the role of adipose-derived tissues in peripheral nerve regeneration and discusses potential advances that would translate this approach into the clinic.

METHODS

We searched PubMed for in vivo, experimental studies on the regenerative effects of adipose-derived tissues on peripheral nerve injuries. We summarized the methods and results for the 42 experiments.

RESULTS

Adipose-derived tissues enhanced peripheral nerve regeneration in 86% of the experiments. Ninety-five percent evaluated purified, cultured, or differentiated adipose tissue. These approaches have regulatory and scaling burdens, restricting clinical usage. Only one experiment tested the ability of adipose tissue to enhance nerve regeneration in conjunction with nerve autografts, the clinical gold standard.

CONCLUSION

Scientific studies illustrate that adipose-derived tissues enhance regeneration of peripheral nerves. Before this approach achieves clinical acceptance, fat processing must become automated and regulatory approval achieved. Animal studies using whole fat grafts are greatly needed for clinical translation.

IGF1 Promotes Adipogenesis by a Lineage Bias of Endogenous Adipose Stem/Progenitor Cells

Adipogenesis is essential for soft tissue reconstruction following trauma or tumor resection. We demonstrate that CD31(-)/34(+)/146(-) cells, a subpopulation of the stromal vascular fraction (SVF) of human adipose tissue, were robustly adipogenic. Insulin growth factor-1 (IGF1) promoted a lineage bias towards CD31(-)/34(+)/146(-) cells at the expense of CD31(-)/34(+)/146(+) cells. IGF1 was microencapsulated in poly(lactic-co-glycolic acid) scaffolds and implanted in the inguinal fat pad of C57Bl6 mice. Control-released IGF1 induced remarkable adipogenesis in vivo by recruiting endogenous cells. In comparison with the CD31(-)/34(+)/146(+) cells, CD31(-)/34(+)/146(-) cells had a weaker Wnt/β-catenin signal. IGF1 attenuated Wnt/β-catenin signaling by activating Axin2/PPARγ pathways in SVF cells, suggesting IGF1 promotes CD31(-)/34(+)/146(-) bias through tuning Wnt signal. PPARγ response element (PPRE) in Axin2 promoter was crucial for Axin2 upregulation, suggesting that PPARγ transcriptionally activates Axin2. Together, these findings illustrate an Axin2/PPARγ axis in adipogenesis that is particularly attributable to a lineage bias towards CD31(-)/34(+)/146(-) cells, with implications in adipose regeneration.

Targeted mesenchymal stem cell and vascular endothelial growth factor strategies for repair of nerve defects with nerve tissue implanted autogenous vein graft conduits

Peripheral nerve gaps exceeding 1 cm require a bridging repair strategy. Clinical feasibility of autogenous nerve grafting is limited by donor site comorbidity. In this study we investigated neuroregenerative efficacy of autogenous vein grafts implanted with tissue fragments from distal nerve in combination with vascular endothelial growth factor (VEGF) or mesenchymal stem cells (MSCs) in repair of rat peripheral nerve defects. Six-groups of Sprague-Dawley rats (n = 8 each) were evaluated in the autogenous setting using a 1.6 cm long peroneal nerve defect: Empty vein graft (group 1), Nerve graft (group 2), Vein graft and nerve fragments (group 3), Vein graft and nerve fragments and blank microspheres (group 4), Vein graft and nerve fragments and VEGF microspheres (group 5), Vein graft and nerve fragments and MSCs (group 6). Nerve fragments were derived from distal segment. Walking track analysis, electrophysiology and nerve histomorphometry were performed for assessment. Peroneal function indices (PFI), electrophysiology (amplitude) and axon count results for group 2 were -9.12 ± 3.07, 12.81 ± 2.46 mV, and 1697.88 ± 166.18, whereas the results for group 5 were -9.35 ± 2.55, 12.68 ± 1.78, and 1566 ± 131.44, respectively. The assessment results did not reveal statistical difference between groups 2 and 5 (P > 0.05). The best outcomes were seen in group 2 and 5 followed by group 6. Compared to other groups, poorest outcomes were seen in group 1 (P ≤ 0.05). PFI, electrophysiology (amplitude) and axon count results for group 1 were -208.82 ± 110.69, 0.86 ± 0.52, and 444.50 ± 274.03, respectively. Vein conduits implanted with distal nerve-derived nerve fragments improved axonal regeneration. VEGF was superior to MSCs in facilitating nerve regeneration. © 2015 Wiley Periodicals, Inc. Microsurgery 36:578-585, 2016.

The sciatic nerve injury model in pre-clinical research

In the pre-clinical view, the study of peripheral nerve repair and regeneration still needs to be carried out in animal models due to the structural complexity of this organ which can be only partly simulated in vitro. The far most used experimental model is based on the injury of the sciatic nerve, the largest nerve trunk in mammals. In this paper, the potential application of the sciatic nerve injury model in pre-clinical research is critically reviewed. This paper is aimed at helping researchers in properly employing this in vivo model for the study of nerve repair and regeneration as well as interpreting the results in a clinical translation perspective.

The effectiveness of tetanus toxin on sciatic nerve regeneration: a preliminary experimental study in rats

OBJECT

The purpose was to investigate the effects of local tetanus toxin (TeTx) application on sciatic nerve regeneration following a rat model of transection injury.

METHODS

After both sciatic nerves were transected and repaired with three epineural sutures, 12 male Wistar albino rats were divided into two groups. 0.25 ml (2.5 flocculation units) TeTx was injected into a piece of absorbable gelatin sponge in TeTx group. In controls, 0.25 ml saline injected. Assessments were performed by using climbing degrees, compound muscle action potentials (CMAPs) and histological parameters (axon number and axonal diameter) 12th week.

RESULTS

CMAPs amplitudes were 11.6 ± 4.7 mV and 1.4 ± 1.3 mV in gastrocnemius and interdigital muscles in TeTx group (5.8 ± 2.4 mV and 0.2 ± 0.1 mV, P < 0.05). Climbing degrees were significantly different (61.6 ± 1.7 vs. 38.3 ± 2.6, P < 0.05). Total axon numbers were higher (1341.1 ± 57.3 vs. 877.5 ± 34.9, P < 0.05) and the mean axon diameter was smaller (4.2 ± 2.1 vs. 2.5 ± 1.9, P < 0.05) in the TeTx group.

CONCLUSION

This preliminary study firstly demonstrated the effectiveness of TeTx on nerve repair in experimental sciatic rat model based on functional, electromyographic and histological parameters.

"Strategic sequences" in adipose-derived stem cell nerve regeneration

BACKGROUND

Peripheral nerve injuries (PNI) are a major source of morbidity worldwide. The development of cellular regenerative therapies has the potential to improve outcomes of nerve injuries. However, an ideal therapy has yet to be found. The purpose of this study is to examine the current literature key points of regenerative techniques using human adipose-derived stem cells (hADSCs) for nerve regeneration and derive a comprehensive approach to hADSC therapy for PNI.

METHODS

A literature review was conducted using the electronic database PubMed to search for current experimental approaches to repairing PNI using hADSCs. Key search elements focused on specific components of nerve regeneration paradigms, including (1) support cells, (2) scaffolds, and (3) nerve conduits.

RESULTS

Strategic sequences were developed by optimizing the components of different experimental regenerative therapies. These sequences focus on priming hADSCs within a specialized growth medium, a hydrogel matrix base, and a collagen nerve conduit to achieve neuromodulatory nerve regeneration. hADSCs may exert their neuroregenerative influence through paracrine effects on surrounding Schwann cells in addition to physical interactions with injured tissue.

CONCLUSIONS

hADSCs may play a key role in nerve regeneration by acting primarily as support for local neurotrophic mediation and modulation of nerve growth rather than that of a primary neuronal differentiation agent.