Research Article: Painful Terminal Neuroma Prevention by Capping PRGD/PDLLA Conduit in Rat Sciatic Nerves

Date Published: March 27, 2018

Publisher: John Wiley and Sons Inc.

Author(s): Jiling Yi, Nan Jiang, Binbin Li, Qiongjiao Yan, Tong Qiu, Killugudi Swaminatha Iyer, Yixia Yin, Honglian Dai, Ali K. Yetisen, Shipu Li.

http://doi.org/10.1002/advs.201700876

Abstract

Neuroma formation after amputation as a long‐term deficiency leads to spontaneous neuropathic pain that reduces quality of life of patients. To prevent neuroma formation, capping techniques are implemented as effective treatments. However, an ideal, biocompatible material covering the nerves is an unmet clinical need. In this study, biocompatible characteristics presented by the poly(D,L‐lactic acid)/arginylglycylaspartic acid (RGD peptide) modification of poly{(lactic acid)‐co‐ [(glycolic acid)‐alt‐(L‐lysine)]} (PRGD/PDLLA) are evaluated as a nerve conduit. After being capped on the rat sciatic nerve stump in vivo, rodent behaviors and tissue structures are compared via autotomy scoring and histological analyses. The PRGD/PDLLA capped group gains lower autotomy score and improves the recovery, where inflammatory infiltrations and excessive collagen deposition are defeated. Transmission electron microscopy images of the regeneration of myelin sheath in both groups show that abnormal myelination is only present in the uncapped rats. Changes in related genes (MPZ, MBP, MAG, and Krox20) are monitored quantitative real‐time polymerase chain reaction (qRT‐PCR) for mechanism investigation. The PRGD/PDLLA capping conduits not only act as physical barriers to inhibit the invasion of inflammatory infiltration in the scar tissue but also provide a suitable microenvironment for promoting nerve repairing and avoiding neuroma formation during nerve recovery.

Partial Text

More than 185 000 limbs are amputated in the United States annually.1 In 2005, the prevalence of limb loss was 1.6 million, which is projected to double by 2050.2 Besides the loss of a body part and its motor function, the majority of patients experience certain level of painful sensation after wound healing. These shock, burning, or electrical‐like pains can persist from months to years and impair patients’ life quality.3 This unsatisfied feeling is aroused by the occurrences of neuromas distributed at the stump of injured nerve.4 For the initial damage in peripheral nerve, residual axons undergo Wallerian degeneration, apoptosis, axons extension, and remyelination to achieve recovery.5 However, this limits regenerative ability that is not sufficient to overcome the long‐distance gap (>50 mm) or fail without the guidance of distal stump, which are typical neuropathic symptoms in serve trauma and amputation.6 In this case, a sprout can be observed at the proximal stump and axon extends spontaneously,7 but they are randomly oriented and chaotic milieu triggers a subsequent disorganization of remyelinations. Finally, a bulbous tissue (neuroma) is formed.8 Within the neuroma, many regenerated axons are surrounded by abnormal myelin sheath, exhibiting variable degrees of thickening, which alters the electrophysiological properties of axons and renders them hypersensitive to mechanical, chemical, and physical stimuli.9 Even worse, this hyperpathia can intensify by the factors that release at the stage of immune reaction, such as monocyte chemoattractant protein‐1, interleukin‐1 (IL‐1), and tumor necrosis factor‐alpha (TNF‐α).10 In prolonged inflammation, collagen and mature myofibroblasts may infiltrate into the neuroma, which acts as the main source of mechanical irritation on regenerating nerves, subsequently generating a persistent painfulness.11

Since the first successful report of peripheral nerve repair in 1836, it has been recognized that not all the nerve injures were amenable to direct end‐to‐end repair as the elasticity was limited.21 According to Seddon classifications for nerve injury, the two worst forms of injury were axonotmesis and neurotmesis, which referred to the presence of a gap in the axon or complete severance of nerve trunk.22 In these situations, surgical repair was often postponed because of the potential suture line dehiscence caused by delayed necrosis.17 Additionally, neuroma might be formed during this interval, which was often accompanied by hyperalgesia, allodynia, and cold intolerance.23 Sometimes extreme pain will cause the function loss of remaining part of body and productivity, resulting in high unemployment as well as high personal and public expenditures.24 For this painful sequel, a series of treatment principles has been developed.14 After the nerve injury, the path‐physiological response of transected nerve such as inflammation factors, growth factors, and scar tissue stimulation leads to neuroma formation, especially the painful neuroma formation at the nerve transection site. A commonly used neuroma prevention approach is shortening; however, its positive effects are very often transitory because of neuroma’s natural tendency to reoccur at the new nerve transection site. Covering the stump, which can be achieved by burying the nerve stump into a nearby anatomic structure or by capping it with different materials, isolates the nerve stump from the environment to obtain a preventive effect on neuroma formation.16, 24 However, high risk of neuroma was formed in the resection.25 To address these issues, nerve guidance capping conduits have been developed for the realignment of two stumps of damaged nerve.26 Some of these nerve capping conduits have the ability of providing a suitable microenvironment for promoting the neural regeneration.17 While different characteristics of the capping materials are needed in clinical applications for different kinds of damaged nerves, especially in amputation, the nerve injury is permanent. Full restoration of function cannot be achieved, due to the absence of whole distal stump.

We have evaluated the effects of PRGD/PDLLA capping conduits on inhibiting the formation of painful neuroma by the analysis of behavior, histological structure, and relative gene expression. The results indicated that inflammatory response, autotomy score, and scar deposition were reduced in the conduit group. Moreover, the myelin morphology of nerve stump capped with the PRGD/PDLLA capping conduits was thick and compact in TEM observation and the relative genes of myelin maturity were also upregulated. These factors contribute to the inhibition of painful neuroma. These changes may be due to the incorporation of RGD‐modified capping materials, which provided a favorable microenvironment for the nerve terminal recovery by inhibiting inflammatory amplification. Therefore, PRGD/PDLLA capping conduits could be a promising alternative used in capping nerve ends to inhibit neuroma formation.

Materials: Poly(D,L‐lactic acid) (PDLLA) (Mw: 250 000) was synthesized in house. Gly‐Arg‐Gly‐Asp‐Gly (RGD) and 1, l‐carbonyldiimidazole were purchased from GL Biochem (China). 1‐Ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide, Masson’s trichrome, and sirius red were purchased from Sigma‐Aldrich. Other chemicals were analytical grade. 3‐0 and 6‐0 monofilament nylon sutures were purchased from Ethicon, Inc. (Johnson & Johnson). SD rats were obtained from the Center for Disease Control and Prevention of Hubei Province (China). Epon 812 was purchased from Electron Microscopy Sciences (Hatfield, PA). Paraformaldehyde, paraffin, glutaraldehyde solution, osmium tetroxide, lead citrate, and uranyl acetate were purchased from Sinopharm Chemical Reagent Co., Ltd (China).

The authors declare no conflict of interest.

 

Source:

http://doi.org/10.1002/advs.201700876

 

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