Better nerve regeneration with distally based fascicular turnover flap than with conventional autologous nerve graft in a rat sciatic nerve defect model

Enhancing Functional Recovery after Segmental Nerve Defect Using Nerve Allograft Treated with Plasma-Derived Exosome

BACKGROUND

Nerve injuries can result in detrimental functional outcomes. Currently, autologous nerve graft offers the best outcome for segmental peripheral nerve injury. Allografts are alternatives, but do not have comparable results. This study evaluated whether plasma-derived exosome can improve nerve regeneration and functional recovery when combined with decellularized nerve allografts.

METHODS

The effect of exosomes on Schwann cell proliferation and migration were evaluated. A rat model of sciatic nerve repair was used to evaluate the effect on nerve regeneration and functional recovery. A fibrin sealant was used as the scaffold for exosome. Eighty-four Lewis rats were divided into autograft, allograft, and allograft with exosome groups. Gene expression of nerve regeneration factors was analyzed on postoperative day 7. At 12 and 16 weeks, rats were subjected to maximum isometric tetanic force and compound muscle action potential. Nerve specimens were then analyzed by means of histology and immunohistochemistry.

RESULTS

Exosomes were readily taken up by Schwann cells that resulted in improved Schwann cell viability and migration. The treated allograft group had functional recovery (compound muscle action potential, isometric tetanic force) comparable to that of the autograft group. Similar results were observed in gene expression analysis of nerve regenerating factors. Histologic analysis showed no statistically significant differences between treated allograft and autograft groups in terms of axonal density, fascicular area, and myelin sheath thickness.

CONCLUSIONS

Plasma-derived exosome treatment of decellularized nerve allograft may provide comparable clinical outcomes to that of an autograft. This can be a promising strategy in the future as an alternative for segmental peripheral nerve repair.

CLINICAL RELEVANCE STATEMENT

Off-the-shelf exosomes may improve recovery in nerve allografts.

Netrin-3 Suppresses Diabetic Neuropathic Pain by Gating the Intra-epidermal Sprouting of Sensory Axons

Diabetic neuropathic pain (DNP) is the most common disabling complication of diabetes. Emerging evidence has linked the pathogenesis of DNP to the aberrant sprouting of sensory axons into the epidermal area; however, the underlying molecular events remain poorly understood. Here we found that an axon guidance molecule, Netrin-3 (Ntn-3), was expressed in the sensory neurons of mouse dorsal root ganglia (DRGs), and downregulation of Ntn-3 expression was highly correlated with the severity of DNP in a diabetic mouse model. Genetic ablation of Ntn-3 increased the intra-epidermal sprouting of sensory axons and worsened the DNP in diabetic mice. In contrast, the elevation of Ntn-3 levels in DRGs significantly inhibited the intra-epidermal axon sprouting and alleviated DNP in diabetic mice. In conclusion, our studies identified Ntn-3 as an important regulator of DNP pathogenesis by gating the aberrant sprouting of sensory axons, indicating that Ntn-3 is a potential druggable target for DNP treatment.

MR microneurography of human peripheral fascicles using a clinical 3T MR scanner

BACKGROUND AND PURPOSE

Knowledge of nerve fascicular structures is essential for managing peripheral nerve disorders. This study aimed to investigate the feasibility of z-axis high-resolution magnetic resonance (MR) microneurography (zH-MRMN) in displaying the three-dimensional structures of tibial nerve fascicles in vivo using a 3T MR scanner.

MATERIALS AND METHODS

Twelve volunteers underwent z-axis conventional-resolution MR microneurography (zC-MRMN) and zH-MRMN of tibial nerves. The visibility scores of the nerve fascicles (VSNFs) on axial zC-MRMN images and axial zH-MRMN multiplanar reformation (MPR) images were compared. The nerve fascicle appearances on the longitudinal zH-MRMN MPR images were described.

RESULTS

In the nerve segments whose long axes were perpendicular to the imaging planes of both zC-MRMN and zH-MRMN, the VSNFs were not significantly different between the axial images of the two modalities (P = 0.083). In the nerve segments whose long axes were not perpendicular to the imaging planes of zC-MRMN, the VSNFs on the axial zC-MRMN images were significantly lower than those on the axial zH-MRMN MPR images that were angled perpendicular to the long axis of the tibial nerve (P < 0.001).

CONCLUSIONS

The longitudinal zH-MRMN MPR images clearly displayed the changing features of the intraneural fascicles as well as the gross morphology of the tibial nerves. zH-MRMN can clearly delineate the topography of the tibial nerve fascicles in vivo through use of a 3T MR scanner.

Localized delivery of brain-derived neurotrophic factor from PLGA microspheres promotes peripheral nerve regeneration in rats

Background

Repair of peripheral nerve defect presents a considerable challenge for reconstructive surgeons. The aim of this study is to develop a brain-derived neurotrophic factor (BDNF) from poly(D,L-lactide-co-glycolide) (PLGA) microspheres for the treatment of the peripheral nerve defect.

Method

BDNF microspheres were prepared by using an oil-in-water emulsification-solvent evaporation method. The morphology, particle size, encapsulation efficiency, drug loading and sustained release performance of microspheres was observed and calculated. Adipose mesenchymal stem cells (ADSCs) were isolated and expanded. ADSCs were divided into four groups: control, BDNF, blank microsphere and BDNF microsphere groups. Cell count kit-8 (CCK-8) assays were used to assess cell proliferation. Cell migration was determined by Transwell assays. Twenty-eight male Sprague–Dawley rats underwent transection damage model on the right sciatic nerve. The wet weight ratio of the gastrocnemius muscle was calculated by comparing the weight of the gastrocnemius muscle from the operated side to that of the normal side. Neuroelectrophysiological testing was performed to assess nerve function recovery. Nerve regeneration was evaluated by histological analysis and immunohistochemical staining.

Results

The microspheres were spherical and had uniform size (46.38 ± 1.00 μm), high encapsulation efficiency and high loading capacity. In vitro release studies showed that BDNF-loaded microspheres had good sustained release characteristics. The duration of BDNF release was extended to more than 50 days. BDNF or BDNF microsphere promote the proliferation and migration of ADSCs than control group (P < 0.05). Compared with control group, BDNF significantly decreased the nerve conduction velocity (NCV) and compound amplitude (AMP) (P < 0.05). The nerve fibers in the BDNF microsphere group were closely arranged and uniformly distributed than control group.

Conclusion

BDNF/PLGA sustained-release microsphere could promote the migration of ADSCs and promoted neural differentiation of ADSCs. Moreover, BDNF/PLGA sustained-release microsphere ameliorated nerve conduction velocity and prevented neuralgic amyotrophy.

Fascicular Turnover Flap: An Approach for Facial Nerve Reconstruction

ABSTRACT

Facial nerve injuries are a common complication associated with parotidectomy. These functionally debilitating injuries are conventionally treated with nonvascularized nerve grafting; however, this reconstructive modality produces moderate donor site morbidity and has limited efficacy for repairing large defects. In addition, nonvascularized nerve grafts are highly susceptible to radiotherapy and require a well-vascularized wound bed to produce adequate therapeutic results. The fascicular turnover flap, described by Koshima et al, utilizes a single fascicle to bridge two nerve endings that are in series with no donor site morbidity. Although studies have demonstrated this technique's efficacy, there is a paucity of data regarding its use in patients undergoing facial nerve reconstruction. Herein, we describe our early clinical experience using the fascicular turnover flap to reconstruct branches of the facial nerve in patients undergoing extensive parotidectomy. Our patients underwent successful reconstruction of the nerve defects produced by parotidectomy using the fascicular turnover flap. Despite postoperative radiotherapy, both patients demonstrated complete functional recovery at six months postoperatively. Although formal head-to-head studies are needed to compare the outcomes of this technique versus conventional nerve grafting for facial nerve reconstruction, our preliminary experiences suggest that the fascicular turnover flap is a viable modality of reconstruction with great potential.

Electrospun polycaprolactone (PCL)-amnion nanofibrous membrane prevents adhesions and promotes nerve repair in a rat model of sciatic nerve compression

Adhesion and scarring after neural surgery are detrimental to nerve regeneration and functional recovery. Amniotic membranes have been used in tissue repair due to their immunogenicity and richness in cytokines. In this study, an electrospun polycaprolactone (PCL)-amnion nanofibrous membrane was prepared for the treatment of sciatic nerve compression in a rat model. The effects of the PCL-amnion nanofibrous membrane on the prevention of adhesion formation and nerve regeneration were evaluated using electrophysiology and histological analyses. Compared with the medical chitosan hydrogel dressing, the PCL-amnion nanofibrous membrane significantly reduced peripheral nerve adhesion and promoted the rapid recovery of nerve conduction. Moreover, the immunohistochemical analysis identified more Schwann cells and less pro-inflammatory M1 macrophages in the PCL-amnion group. Western blot and RT-PCR results showed that the expression levels of type-Ⅰ and Ⅲ collagen in the PCL-treated rats were half of those in the control group after 12 weeks, while the expression level of nerve growth factor was approximately 3.5 times that found in the rats treated with medical chitosan hydrogel. In summary, electrospun PCL-amnion nanofibrous membranes can effectively reduce adhesion after neural surgery and promote nerve repair and regeneration. The long-term retention in vivo and sustained release of cytokines make PCL-amnion a promising biomaterial for clinical application.

Vascularized Muscle Flap to Reduce Wound Breakdown During Flexible Electrode-Mediated Functional Electrical Stimulation After Peripheral Nerve Injury

The success of devices delivering functional electrical stimulation (FES) has been hindered by complications related to implants including skin breakdown and subsequent wound dehiscence. Our hypothesis was that a vascularized muscle flap along the dorsal surface of an epimysial electrode would prevent skin breakdown during FES therapy to treat atrophy of the gastrocnemius muscle during peripheral nerve injury. Resection of a tibial nerve segment with subsequent electrode implantation on the dorsal surfaces of the gastrocnemius muscle was performed on ten Lewis rats. In five rats, the biceps femoris (BF) muscle was dissected and placed along the dorsal surface of the electrode (Flap group). The other five animals did not undergo flap placement (No Flap group). All animals were treated with daily FES therapy for 2 weeks and degree of immune response and skin breakdown were evaluated. The postoperative course of one animal in the No Flap group was complicated by complete wound dehiscence requiring euthanasia of the animal on postoperative day 4. The remaining 4 No Flap animals showed evidence of ulceration at the implant by postoperative day 7. The 5 animals in the Flap group did not have ulcerative lesions. Excised tissue at postoperative day 14 examined by histology and in vivo Imaging System (IVIS) showed decreased implant-induced inflammation in the Flap group. Expression of specific markers for local foreign body response were also decreased in the Flap group.