Peripheral Nerve Injury In Rats Research Articles

Effect of mesenchymal stem cells and melatonin on experimentally induced peripheral nerve injury in rats

Injury of a peripheral nerve (PNI) leads to both ischemic and inflammatory alterations. Sciatic nerve injury (SNI) represents the most widely used model for PNI. Mesenchymal stem cell-based therapy (MSCs) has convenient properties on PNI by stimulating the nerve regeneration. Melatonin has cytoprotective activity. The neuroprotective characteristics of MSCs and melatonin separately or in combination remain a knowledge need. In the rats-challenged SNI, therapeutic roles of intralesional MSCs and intraperitoneal melatonin injections were evaluated by functional assessment of peripheral nerve regeneration by walking track analysis involving sciatic function index (SFI) and two electrophysiological tests, electromyography and nerve conduction velocity, as well as measurement of antioxidant markers in serum, total antioxidant capacity (TAC) and malondialdehyde, and mRNA expression of brain derived neurotrophic factor (BDNF) in nerve tissues in addition to the histopathological evaluation of nerve tissue. Both individual and combination therapy with MSCs and melatonin therapies could effectively ameliorate this SNI and promote its regeneration as evidenced by improving the SFI and two electrophysiological tests and remarkable elevation of TAC with decline in lipid peroxidation and upregulation of BDNF levels. All of these led to functional improvement of the damaged nerve tissues and good recovery of the histopathological sections of sciatic nerve tissues suggesting multifactorial synergistic approach of the concurrent usage of melatonin and MSCs in PNI. The combination regimen has the most synergistic neuro-beneficial effects in PNI that should be used as therapeutic option in patients with PNI to boost their quality of life.

Post-treatment with maropitant reduces oxidative stress, endoplasmic reticulum stress and neuroinflammation on peripheral nerve injury in rats.

To determine the effective dose and therapeutic potential of maropitant using through expression of mediators of oxidative stress, inflammatory and of the unfolded protein response (UPR) (bio) markers on spinal cord using a model of neuropathic pain induced through chronic constriction injury (CCI) in rats. Randomized, blinded, prospective experimental study. 98 male Wistar rats. Rats were anesthetized with sevoflurane and after CCI, they were randomly assigned to the following groups that received: vehicle, 3, 6, 15, 30 e 50 mg/kg/24q of maropitant. The effect on inflammatory mediators (IL10, TNFα), oxidative stress (GPx, CAT, SOD), microglial (IBA-1) and neuronal (NeuN, TACR1) markers was evaluated though immunohistochemistry and expression levels of markers of hypoxia (HIF1α, Nrf2), antioxidant enzymes (Catalse, Sod1 and GPx1), and endoplasmic reticulum stress mediators (GRP78, CHOP and PERK) through qRT-PCR. Intraperitoneal injection (IP) of maropitant inhibited nociception with ID50 values of 4,1 mg/kg (5,85-19,36) in a neuropathic pain model through CCI. A dose of 30 mg/kg/24q was significantly effective in reducing mechanical allodynia 1 to 4h after treatment with nociception inhibition (145,83%). A reduction in the expression of hypoxia factors (HIF1α, Nrf2) was observed, along with an increase in antioxidant activity (CAT, SOD and GPX). Additionally, there was a reduction in inflammatory markes (IL10, TNFα), microglial (IBA-1), and neuronal markers (NeuN, TACR1). These findings demonstrate that the determined dose, administered daily for seven days, had an antinociceptive effect, as well as anti-inflammatory and antioxidant activity.

Effectiveness of Low Level Laser Therapy and Low Intensity Pulsed Ultrasound on Neuropathic Pain among the Experimentally Induced Peripheral Nerve Injury in Rat Model

Background: Peripheral nerve injury creates an impact on the inflammatory process, leading to an elevation inHypoxia-inducible factor-1 alpha levels, which contributes to the development and progression of neuropathicpain. An innovative approach to alleviating neuropathic pain involves targeting inflammation.Purpose: This study aims to compare the effect of Low-Level Laser Therapy (LLLT) and Low-Intensity PulsedUltrasound (LIPUS) on neuropathic pain among the experimentally induced peripheral nerve injury in rat model.Methods: Rats with induced sciatic nerve crush injury were randomly divided into three groups: control, LIPUStreatment, and LLLT treatment. Mechanical paw withdrawal threshold analysis was performed before the injuryand from POD 2nd, 7th, 14th, and 21st to assess effectiveness of the treatment.Result: Low-Level Laser Therapy (LLLT) group showing statistically greater improvement on POD 14 and 21compared to both the LIPUS group and the control group in terms of paw withdrawal threshold measurementsamong rats with crush-induced neuropathic pain (P < 0.001).Conclusion: This study found that the use of LLLT has a beneficial effect in the management of neuropathic painand control of analgesia compared to LIPUS by inhibiting the upregulation of HIF-1α synthesis during ischemia,hypoxia, and inflammation. However further studies are recommended to analyze long term results in largersample to control neuropathic pain.

Human umbilical cord mesenchymal stem cell-derived exosomes loaded into a composite conduit promote functional recovery after peripheral nerve injury in rats.

Complete transverse injury of peripheral nerves is challenging to treat. Exosomes secreted by human umbilical cord mesenchymal stem cells are considered to play an important role in intercellular communication and regulate tissue regeneration. In previous studies, a collagen/hyaluronic acid sponge was shown to provide a suitable regeneration environment for Schwann cell proliferation and to promote axonal regeneration. This three-dimensional (3D) composite conduit contains a collagen/hyaluronic acid inner sponge enclosed in an electrospun hollow poly (lactic-co-glycolic acid) tube. However, whether there is a synergy between the 3D composite conduit and exosomes in the repair of peripheral nerve injury remains unknown. In this study, we tested a comprehensive strategy for repairing long-gap (10 mm) peripheral nerve injury that combined the 3D composite conduit with human umbilical cord mesenchymal stem cell-derived exosomes. Repair effectiveness was evaluated by sciatic functional index, sciatic nerve compound muscle action potential recording, recovery of muscle mass, measuring the cross-sectional area of the muscle fiber, Masson trichrome staining, and transmission electron microscopy of the regenerated nerve in rats. The results showed that transplantation of the 3D composite conduit loaded with human umbilical cord mesenchymal stem cell-derived exosomes promoted peripheral nerve regeneration and restoration of motor function, similar to autograft transplantation. More CD31-positive endothelial cells were observed in the regenerated nerve after transplantation of the loaded conduit than after transplantation of the conduit without exosomes, which may have contributed to the observed increase in axon regeneration and distal nerve reconnection. Therefore, the use of a 3D composite conduit loaded with human umbilical cord mesenchymal stem cell-derived exosomes represents a promising cell-free therapeutic option for the treatment of peripheral nerve injury.

Effect of folic acid coated-crosslinked urethane-doped polyester elastomer nerve conduit on promoting the repair of long distance peripheral nerve injury in rats

To investigate the effect of folic acid coated-crosslinked urethane-doped polyester elastomer (fCUPE) nerve conduit in repairing long distance peripheral nerve injury. Thirty-six 3-month-old male Sprague Dawley rats weighing 180-220 g were randomly assigned to 3 groups, each consisting of 12 rats: CUPE nerve conduit transplantation group (group A), fCUPE nerve conduit transplantation group (group B), and autologous nerve transplantation group (group C), the contralateral healthy limb of group C served as the control group (group D). A 20-mm-long sciatic nerve defect model was established in rats, and corresponding materials were used to repair the nerve defect according to the group. The sciatic function index (SFI) of groups A-C was calculated using the Bain formula at 1, 2, and 3 months after operation. The nerve conduction velocity (NCV) of the affected side in groups A-D was assessed using neuroelectrophysiological techniques. At 3 months after operation, the regenerated nerve tissue was collected from groups A-C for S-100 immunohistochemical staining and Schwann cell count in groups A and B to compare the level of nerve repair and regeneration in each group. At 3 months after operation, the nerve conduits in all groups partially degraded. There was no significant adhesion between the nerve and the conduit and the surrounding tissues, the conduit was well connected with the distal and proximal nerves, and the nerve-like tissues in the conduit could be observed when the nerve conduit stents were cut off. SFI in group A was significantly higher than that in group C at each time point after operation and was significantly higher than that in group B at 2 and 3 months after operation ( P<0.05). There was no significant difference in SFI between groups B and C at each time point after operation ( P>0.05). NCV in group A was significantly slower than that in the other 3 groups at each time point after operation ( P<0.05). The NCV of groups B and C were slower than that of group D, but the difference was significant only at 1 month after operation ( P<0.05). There was no significant difference between groups B and C at each time point after operation ( P>0.05). Immunohistochemical staining showed that the nerve tissue of group A had an abnormal cavo-like structure, light tissue staining, and many non-Schwann cells. In group B, a large quantity of normal neural structures was observed, the staining was deeper than that in group A, and the distribution of dedifferentiated Schwann cells was obvious. In group C, the nerve bundles were arranged neatly, and the tissue staining was the deepest. The number of Schwann cells in group B was (727.50±57.60) cells/mm 2, which was significantly more than that in group A [(298.33±153.12) cells/mm 2] ( t=6.139, P<0.001). The fCUPE nerve conduit is effective in repairing long-distance sciatic nerve defects and is comparable to autologous nerve grafts. It has the potential to be used as a substitute material for peripheral nerve defect transplantation.

Inhibition of Schwann Cell Pyroptosis Promotes Nerve Regeneration in Peripheral Nerve Injury in Rats.

Peripheral nerve injury (PNI) is one of the most debilitating injuries, but therapies for PNI are still far from satisfactory. Pyroptosis, a recently identified form of cell death, has been demonstrated to participate in different diseases. However, the role of pyroptosis of Schwann cells in PNI remains unclear. We established a rat PNI model, and western blotting, transmission electron microscopy, and immunofluorescence staining were used to confirm pyroptosis of Schwann cells in PNI in vivo. In vitro, pyroptosis of Schwann cells was induced by lipopolysaccharides (LPS)+adenosine triphosphate disodium (ATP). An irreversible inhibitor of pyroptosis, acetyl (Ac)-Tyr-Val-Ala-Asp-chloromethyl ketone (Ac-YVAD-cmk), was used to attenuate Schwann cell pyroptosis. Moreover, the influence of pyroptotic Schwann cells on the function of dorsal root ganglion neurons (DRGns) was analyzed by a coculture system. Finally, the rat PNI model was intraperitoneally treated with Ac-YVAD-cmk to observe the effect of pyroptosis on nerve regeneration and motor function. Schwann cell pyroptosis was notably observed in the injured sciatic nerve. LPS+ATP treatment effectively induced Schwann cell pyroptosis, which was largely attenuated by Ac-YVAD-cmk. Additionally, pyroptotic Schwann cells inhibited the function of DRGns by secreting inflammatory factors. A decrease in pyroptosis in Schwann cells promoted regeneration of the sciatic nerve and recovery of motor function in rats. Given the role of Schwann cell pyroptosis in PNI progression, inhibition of Schwann cell pyroptosis might be a potential therapeutic strategy for PNI in the future.

NPS-Crosslinked Fibrin Gels Load with EMSCs to Repair Peripheral Nerve Injury in Rats.

Neural tissue engineering has been introduced as a novel therapeutic strategy for trauma-induced sciatic nerve defects. Here, a neuropeptide S (NPS)-crosslinked fibrin scaffolds (NPS@Fg) loaded with an ectomesenchymal stem cell (EMSC) system to bridge an 8-mm sciatic nerve defect in rats are reported. The Schwann cell-like and neural differentiation of the EMSCs on the engineered fibrin scaffolds are also assessed in vitro. These results show that the NPS@Fg promotes the differentiation of EMSCs into neuronal lineage cells, which may also contribute to the therapeutic outcome of the NPS@Fg+EMSCs strategy. After transplantation NPS@Fg+EMSCs into sciatic nerve defects in rats, nerve recovery is assessed up to 12 weeks postinjury. In vivo experiments show that the combination of NPS crosslinked fibrin scaffolds with EMSCs can significantly accelerate nerve healing and improve morphological repair. In the study, NPS@Fg+EMSCs may represent a new potential strategy for peripheral nerve reconstruction.

Neural grafts containing exosomes derived from Schwann cell-like cells promote peripheral nerve regeneration in rats

Schwann cell-like cells (SCLCs), differentiated from mesenchymal stem cells, have shown promising outcomes in the treatment of peripheral nerve injuries in preclinical studies. However, certain clinical obstacles limit their application. Hence, the primary aim of this study was to investigate the role of exosomes derived from SCLCs (SCLCs-exo) in peripheral nerve regeneration. SCLCs were differentiated from human amniotic mesenchymal stem cells (hAMSCs) in vitro and validated by immunofluorescence, real-time quantitative PCR and western blot analysis. Exosomes derived from hAMSCs (hAMSCs-exo) and SCLCs were isolated by ultracentrifugation and validated by nanoparticle tracking analysis, WB analysis and electron microscopy. A prefabricated nerve graft was used to deliver hAMSCs-exo or SCLCs-exo in an injured sciatic nerve rat model. The effects of hAMSCs-exo or SCLCs-exo on rat peripheral nerve injury (PNI) regeneration were determined based on the recovery of neurological function and histomorphometric variation. The effects of hAMSCs-exo or SCLCs-exo on Schwann cells were also determined via cell proliferation and migration assessment. SCLCs significantly expressed the Schwann cell markers glial fibrillary acidic protein and S100. Compared to hAMSCs-exo, SCLCs-exo significantly enhanced motor function recovery, attenuated gastrocnemius muscle atrophy and facilitated axonal regrowth, myelin formation and angiogenesis in the rat model. Furthermore, hAMSCs-exo and SCLCs-exo were efficiently absorbed by Schwann cells. However, compared to hAMSCs-exo, SCLCs-exo significantly promoted the proliferation and migration of Schwann cells. SCLCs-exo also significantly upregulated the expression of a glial cell-derived neurotrophic factor, myelin positive regulators (SRY-box transcription factor 10, early growth response protein 2 and organic cation/carnitine transporter 6) and myelin proteins (myelin basic protein and myelin protein zero) in Schwann cells. These findings suggest that SCLCs-exo can more efficiently promote PNI regeneration than hAMSCs-exo and are a potentially novel therapeutic approach for treating PNI.

Glucocorticoid Receptor/HCN4 Channels Interaction in Spinal Dorsal Horn Participates in the Regulation of Neuropathic Pain after Peripheral Nerve Injury in Rats.

We studied the interaction between glucocorticoid receptor (GR) and HCN4 channels in the rat model of spared nerve injury (SNI) in Sprague-Dawley rats (n=124). The animals were randomly divided into 6 groups: sham-operated (SO; n=24), SNI (reference group; n=20), and 4 experimental SNI groups intrathecally treated with dexamethasone (DEX; GR agonist; n=20), RU38486 (GR antagonist; n=20), ZD7288 (HCN channels blocker; n=20), and ZD7288+DEX (n=20). The paw mechanical withdrawal threshold (PWT) was measured one day before surgery (SO group) and on days 1, 3, 7, 14, and 21 after surgery. Behavioral results showed that mechanical hyperalgesia appeared on day 1 after SNI, while PWT decreased gradually with time. The expression of GR and HCN4 channels in L4-L6 dorsal horn of the spinal cord was detected by Western blotting and immunohistochemistry. In the reference group, SNI significantly increased GR expression up to day 14 after surgery in comparison with the SO group. The expression of GR showed a tendency to increase in the DEX group (with the maximum expression on days 14 and 21), significantly increased in the RU38486 group (maximum on day 7). In the ZD7288 group, GR expression was lower than in the SNI group and did not change throughout the experiment, suggesting that ZD7288 could block the expression of GR. In the DEX group, the expression of HCN4 channels was significantly higher on day 1 after SNI, but there were no differences in this parameter between the RU38486 and ZD7288 groups. In the ZD7288+DEX group, the expression of HCN4 channels significantly increased on days 14 and 21 after SNI. Thus, GR and HCN4 have the same linkage in the formation of central sensitization after SNI, but antagonists have no significant effect on the improvement of pain behavior.

Human Adipose-Derived Stem Cells Delay Muscular Atrophy after Peripheral Nerve Injury in Rats.

Given that denervation atrophy often occurs in muscle after peripheral nerve injury, the effects of injections of human adipose-derived stem cells (hADSCs) and platelet-rich plasma (PRP) into muscle after peripheral nerve injury were examined. hADSCs were isolated from human subcutaneous fat tissue, and PRP was prepared from rat whole blood before injection into a rat sciatic nerve injury model. Muscle atrophy was evaluated by quantitating the gross musculature and muscle fiber area and walking footprint analysis. At 4 weeks post-surgery, there were significant differences in the sciatic functional index between experimental (injected with hADSCs, PRP, or combined hADSCs + PRP) and non-operated groups (p < 0.0001), but no significant differences were observed between the different treatment groups (p > 0.05). Post hoc Bonferroni tests also showed significant differences in the wet muscle weight ratios of hADSC, PRP, and combined groups compared to PBS group. The gastrocnemius muscle fiber area was larger in hADSC group and the combined group compared to PBS group at 4 weeks post-surgery. The injection of hADSCs delays muscular atrophy after sciatic nerve injury in rats; thus, hADSCs are a promising alternative for regenerating atrophied muscle.

Activation of Double-Stranded RNA-Activated Protein Kinase in the Dorsal Root Ganglia and Spinal Dorsal Horn Regulates Neuropathic Pain Following Peripheral Nerve Injury in Rats.

Double-stranded RNA (dsRNA)-activated kinase (PKR) is an important component in inflammation and immune dysfunction. However, the role of PKR in neuropathic pain remains unclear. Here, we showed that lumbar 5 spinal nerve ligation (SNL) led to a significant increase in the level of phosphorylated PKR (p-PKR) in both the dorsal root ganglia (DRG) and spinal dorsal horn. Images of double immunofluorescence staining revealed that p-PKR was expressed in myelinated A-fibers, unmyelinated C-fibers, and satellite glial cells in the DRG. In the dorsal horn, p-PKR was located in neuronal cells, astrocytes, and microglia. Data from behavioral tests showed that intrathecal (i.t.) injection of 2-aminopurine (2-AP), a specific inhibitor of PKR activation, and PKR siRNA prevented the reductions in PWT and PWL following SNL. Established neuropathic pain was also attenuated by i.t. injection of 2-AP and PKR siRNA, which started on day 7 after SNL. Prior repeated i.t. injections of PKR siRNA prevented the SNL-induced degradation of IκBα and IκBβ in the cytosol and the nuclear translocation of nuclear factor κB (NF-κB) p65 in both the DRG and dorsal horn. Moreover, the SNL-induced increase in interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) production was diminished by this treatment. Collectively, these results suggest that peripheral nerve injury-induced PKR activation via NF-κB signaling-regulated expression of proinflammatory cytokines in the DRG and dorsal horn contributes to the pathogenesis of neuropathic pain. Our findings suggest that pharmacologically targeting PKR might be an effective therapeutic strategy for the treatment of neuropathic pain.

Analgesic effect of recombinant GABAergic precursors releasing ω-conotoxin MVIIA in a model of peripheral nerve injury in rats.

Development of chronic pain has been attributed to dysfunctional GABA signaling in the spinal cord. Direct pharmacological interventions on GABA signaling are usually not very efficient and often accompanied by side effects due to the widespread distribution of GABA receptors in CNS. Transplantation of GABAergic neuronal cells may restore the inhibitory potential in the spinal cord. Grafted cells may also release additional analgesic peptides by means of genetic engineering to further enhance the benefits of this approach. Conopeptides are ideal candidates for recombinant expression using cell-based strategies. The omega-conopeptide MVIIA is in clinical use for severe pain marketed as FDA approved Prialt in the form of intrathecal injections. The goal of this study was to develop transplantable recombinant GABAergic cells releasing conopeptide MVIIA and to evaluate the analgesic effect of the grafts in a model of peripheral nerve injury-induced pain. We have engineered and characterized the GABAergic progenitors expressing MVIIA. Recombinant and nonrecombinant cells were intraspinally injected into animals after the nerve injury. Animals were tested weekly up to 12 weeks for the presence of hypersensitivity, followed by histochemical and biochemical analysis of the tissue. We observed beneficial effects of the grafted cells in reducing hypersensitivity in all grafted animals, especially potent in the recombinant group. The level of pain-related cytokines was reduced in the grafted animals and correlation between these pain markers and actual behavior was indicated. This study demonstrated the feasibility of recombinant cell transplantation in the management of chronic pain.

The effect of poly(lactic-co-glycolic acid) conduit loading insulin-like growth factor 1 modified by a collagen-binding domain on peripheral nerve injury in rats.

Peripheral nerve injury (PNI) exists widely and seriously affects patients' daily lives. However, the effect of nerve repair is still limited, and only 50% of patients can recover useful functions. To overcome these obstacles, collagen-coated poly(lactic-co-glycolic acid) (PLGA) conduits loaded with CBD-IGF-1 were designed and tested in vitro and in vivo. The physical characterization of the conduit was tested by scanning electron microscopy, and the static water contact angle, release rate, and nerve regeneration ability of the conduit were verified in a rat sciatic nerve injury model. The results showed that the PLGA/col/CBD-IGF-1 conduit had a rough surface and good hydrophilicity. CBD-IGF-1 could be released slowly from the PLGA/col/CBD-IGF-1 conduit. In the in vivo experiment, gait analysis and electrophysiological evaluation showed that the sciatic functional index and electrophysiological parameters were best in the group treated with the PLGA/col/CBD-IGF-1 conduit. The pathological examination results for the sciatic nerve and gastrocnemius muscle in the group treated with the PLGA/col/CBD-IGF-1 conduit were better than those in the other three groups. In short, this study demonstrated the beneficial effects of CBD-IGF-1 in nerve regeneration. The PLGA/col/CBD-IGF-1 conduit has therapeutic potential for use in the treatment of PNI.

P.0296 Sex-dependent antinociceptive effects of fatty acid amide hydrolase but not monoacyl glycerol lipase inhibition following peripheral nerve injury in rats

P.0296 Sex-dependent antinociceptive effects of fatty acid amide hydrolase but not monoacyl glycerol lipase inhibition following peripheral nerve injury in rats

Cotinine Effects on Peripheral Nerve Injuries: An Experimental Study

Aim: Cigarette smoking is a common addictive manner and one of the greatest threats to health. Nicotine is one of the main components of cigarette. The aim of this study was to reveal the effect of cotinine which is an active metabolite of nicotine, on peripheral nerve injury in rats. Material and Methods: We studied 42 male adult albino-Wistar rats that were divided into three groups with simple randomization method. Group 1 were given Cotinine® (C-5923-sigma) intraperitoneally, at a dose of 0.3 mg/kg/day for 21 days. Group 2 were given ethyl alcohol, the solvent of Cotinine in the same way, dose and period. Group 3 were subjected to sciatic nerve compression injury by a clip, which has a closing pressure of 50 gr/cm2. Group 1 and 2 were subjected to the same type of injury at the end of 21 days. Four weeks later after trauma, both three groups were sacrificed and injured sciatic nerve sections are taken for histopathological analysis. Results: It was observed that cotinine aggravated the traumatic degeneration and as privileged caused to fibrosis. In the Schwann cells of thick-myelinated fibers exhibited higher grades of degeneration and mitochondrial augmentation. According to the multiple comparison results, the number of Wallerian degenerations in the trauma group was significantly lower than in both the drug-control (p=0.016) and drug (p&amp;lt;0.001) groups. This situation was estimated as a response to oxidative stress. Conclusion: This study reveals that peripheral nerve regeneration after traumatic injury may be affected negatively in smokers.

Astrocytic c-Jun N-terminal kinase-histone deacetylase-2 cascade contributes to glutamate transporter-1 decrease and mechanical allodynia following peripheral nerve injury in rats

Decrease of glutamate transporter-1 (GLT-1) in the spinal dorsal horn after nerve injury induces enhanced excitatory transmission and causes persistent pain. Histone deacetylases (HDACs)-catalyzed deacetylation might contribute to the decrease of GLT-1, while the detailed mechanisms have yet to be fully elaborated. Spinal nerve ligation (SNL) induced significant increases of HDAC2 and decreases of GLT-1 in spinal astrocytes. Intrathecal infusion of the HDAC2 inhibitors attenuated the decrease of GLT-1 and enhanced phosphorylation of glutamate receptors. GLT-1 and phosphorylated c-Jun N-terminal kinase (JNK) were highly colocalized in the spinal cord, and a large number of pJNK positive cells were HDAC2 positive. Intrathecally infusion of the JNK inhibitor SP600125 significantly inhibited SNL-induced upregulation of HDAC2. SNL-induced HDAC2 up-regulation could be inhibited by the neutralizing anti-tumor necrosis factor-α (TNF-α) binding protein etanercept or the microglial inhibitor minocycline. In cultured astrocytes, TNF-α induced enhanced phosphorylation of JNK and a significant increase of HDAC2, as well as a remarkable decrease of GLT-1, which could be prevented by SP600125 or the HDAC2 specific inhibitor CAY10683. Our data suggest that astrocytic JNK-HDAC2 cascade contributes to GLT-1 decrease and mechanical allodynia following peripheral nerve injury. Neuroimmune activation after peripheral nerve injury could induce epigenetic modification changes in astrocytes and contribute to chronic pain maintenance.

Inhibition of ferroptosis-like cell death attenuates neuropathic pain reactions induced by peripheral nerve injury in rats.

Relationships between iron-dependent ferroptosis and nerve system diseases have been recently revealed. However, the role of ferroptosis in neuropathic pain (NeP) remains to be elucidated. Thus, we aimed to investigate whether ferroptosis in spinal cord contributes to NeP induced by a chronic constriction injury (CCI) of the sciatic nerve. Forty Sprague-Dawley rats received CCI or sham surgery, and were randomly assigned to the following four groups: sham group; CCI+LIP group; CCI+Veh group; and CCI group. Liproxstatin-1 or corn oil were separately injected intraperitoneally for three consecutive days after surgery in the CCI+LIP or CCI+Veh group. The mechanical and thermal hypersensitivities were tested after surgery. Biochemical and morphological changes related to ferroptosis in the spinal cord were also assessed. These included iron content, glutathione peroxidase 4 (GPX4) and anti-acyl-CoA synthetase long-chain family member 4 (ACSL4) expression, lipid peroxidation assays, as well as mitochondrial morphology. CCI-induced NeP was followed by iron accumulation, increased lipid peroxidation and dysregulation of ACSL4 and GPX4. Moreover transmission electron microscopy confirmed the presence of aberrant morphological changes on mitochondrial, such as mitochondria shrinkage and membrane rupture. Furthermore, the administration of liproxstatin-1 on CCI rats attenuated hypersensitivities, lowered the iron level, decreased spinal lipid peroxidation, restored the dysregulations in GPX4 and ACSL4 levels, and protected against CCI induced morphological changes in mitochondria. Our findings indicated the involvement of ferroptosis in CCI induced NeP, and point to ferroptosis inhibitors such as liproxstatin-1 as potential therapies for hypersensitivity induced by peripheral nerve injury. The spinal ferroptosis-like cell death was involved in the development of neuropathic pain resulted from peripheral nerve injury, and inhibition of ferroptosis by liproxstatin-1 could alleviate mechanical and thermal hypersensitivities. This knowledge suggested that ferroptosis could represent a potential therapeutic target for neuropathic pain.

Coordinated changes in the expression of Wnt pathway genes following human and rat peripheral nerve injury.

A human neuroma-in continuity (NIC), formed following a peripheral nerve lesion, impedes functional recovery. The molecular mechanisms that underlie the formation of a NIC are poorly understood. Here we show that the expression of multiple genes of the Wnt family, including Wnt5a, is changed in NIC tissue from patients that underwent reconstructive surgery. The role of Wnt ligands in NIC pathology and nerve regeneration is of interest because Wnt ligands are implicated in tissue regeneration, fibrosis, axon repulsion and guidance. The observations in NIC prompted us to investigate the expression of Wnt ligands in the injured rat sciatic nerve and in the dorsal root ganglia (DRG). In the injured nerve, four gene clusters were identified with temporal expression profiles corresponding to particular phases of the regeneration process. In the DRG up- and down regulation of certain Wnt receptors suggests that nerve injury has an impact on the responsiveness of injured sensory neurons to Wnt ligands in the nerve. Immunohistochemistry showed that Schwann cells in the NIC and in the injured nerve are the source of Wnt5a, whereas the Wnt5a receptor Ryk is expressed by axons traversing the NIC. Taken together, these observations suggest a central role for Wnt signalling in peripheral nerve regeneration.

A meta-analysis of functional outcomes in rat sciatic nerve injury models.

Rat sciatic nerve injury (PNR) is the most utilized model in studies on peripheral nerve regeneration. However, large animal models are increasingly favored based on the assumption that nerve regeneration in rodents achieves more favorable outcomes than in humans. The purpose of this meta-analysis was to investigate which rat PNR models are more stringent and should be used before utilizing large animal experimentation. A PRISMA-guided meta-analysis of the English literature regarding functional outcomes in rat peripheral nerve injury models was conducted. Outcomes of five basic scenarios: (1) transected nerve/negative control, (2) transection with primary microsurgical repair, (3) isogenic/autologous grafts, (4) acellular-allogenic grafts, and (5) limb transplantation were compared to sciatic nerves without any intervention/positive control. Outcomes were compared using Sciatic Functional Index (SFI). Log-based projections were generated and evaluated using mean squared error (MSE), one-way-ANOVA, and Tukey-HSD post-hoc analysis. In total, 167 articles met the inclusion criteria. The earliest manifestations of motor recovery were encountered in the transection and primary repair group (p <.0005). There was a significant difference in recovery time and degree of recovery between all surgical models (p <.0005). At 24 weeks, the SFI in hindlimb transplantation group was significantly worse than all other groups (-74.07 ± 2.74, p <.0005). Autografts smaller than 10 mm recovered sooner than autografts longer than 10 mm (p = .021) and autografts recovered faster than allografts. This meta-analysis does not support the belief that neuro-regeneration is exceptional in transection models. These models remain adequate to provide translatable information and should initially be used in investigational studies.

ISP and PAP4 peptides promote motor functional recovery after peripheral nerve injury.

Both intracellular sigma peptide (ISP) and phosphatase and tensin homolog agonist protein (PAP4) promote nerve regeneration and motor functional recovery after spinal cord injury. However, the role of these two small peptides in peripheral nerve injury remains unclear. A rat model of brachial plexus injury was established by crush of the C6 ventral root. The rats were then treated with subcutaneous injection of PAP4 (497 µg/d, twice per day) or ISP (11 µg/d, once per day) near the injury site for 21 successive days. After ISP and PAP treatment, the survival of motoneurons was increased, the number of regenerated axons and neuromuscular junctions was increased, muscle atrophy was reduced, the electrical response of the motor units was enhanced and the motor function of the injured upper limbs was greatly improved in rats with brachial plexus injury. These findings suggest that ISP and PAP4 promote the recovery of motor function after peripheral nerve injury in rats. The animal care and experimental procedures were approved by the Laboratory Animal Ethics Committee of Jinan University of China (approval No. 20111008001) in 2011.