Curcumin upregulates S100 expression and improves regeneration of the sciatic nerve following its complete amputation in mice

Sustainable Release Selenium Laden with SiO2 Restoring Peripheral Nerve Injury via Modulating PI3K/AKT Pathway Signaling Pathway

Background

Inhibiting ROS overproduction is considered a very effective strategy for the treatment of peripheral nerve injuries, and Se has a remarkable antioxidant effect; however, since the difference between the effective concentration of Se and the toxic dose is not large, we synthesized a nanomaterial that can release Se slowly so that it can be used more effectively.

Methods

Se@SiO2 NPs were synthesized using a mixture of Cu2-x Se nanocrystals, and the mechanism of action of Se@SiO2 NPs was initially explored by performing sequencing, immunofluorescence staining and Western blotting of cellular experiments. The mechanism of action of Se@SiO2 NPs was further determined by performing behavioral assays after animal experiments and by sampling the material for histological staining, immunofluorescence staining, and ELISA. The effects, mechanisms and biocompatibility of Se@SiO2 NPs for peripheral nerve regeneration were determined.

Results

Porous Se@SiO2 was successfully synthesized, had good particle properties, and could release Se slowly. CCK-8 experiments revealed that the optimal experimental doses were 100 μM H2O2 and 200 μg/mL Se@SiO2, and RNA-seq revealed that porous Se@SiO2 was associated with cell proliferation, apoptosis, and the PI3K/AKT pathway. WB showed that porous Se@SiO2 could increase the expression of cell proliferation antigens (PCNA and S100) and antiapoptotic proteins (Bcl-2), decrease the expression of proapoptotic proteins (Bax), and increase the expression of antioxidative stress proteins (Nrf2, HO-1, and SOD2). EdU cell proliferation and ROS fluorescence assays showed that porous Se@SiO2 promoted cell proliferation and reduced ROS levels. The therapeutic effect of LY294002 (a PI3K/AKT pathway inhibitor) was decreased significantly and its effect was lost when it was added simultaneously with porous Se@SiO2. Animal experiments revealed that the regenerated nerve fiber density, myelin thickness, axon area, gastrocnemius muscle wet-to-weight ratio, myofiber area, sciatic nerve function index (SFI), CMAP, apoptotic cell ratio, and levels of antioxidative stress proteins and anti-inflammatory factors were increased following the administration of porous Se@SiO2. The levels of oxidative stress proteins and anti-inflammatory factors were significantly greater in the Se@SiO2 group than in the PNI group, and the effect of LY294002 was decreased significantly and was lost when it was added simultaneously with porous Se@SiO2.

Conclusion

Se@SiO2 NPs are promising, economical and effective Se-releasing nanomaterials that can effectively reduce ROS production, inhibit apoptosis and promote cell proliferation after nerve injury via the PI3K/AKT pathway, ultimately accelerating nerve regeneration. These findings could be used to design new, promising drugs for the treatment of peripheral nerve injury.

Pulsed electromagnetic field-assisted reduced graphene oxide composite 3D printed nerve scaffold promotes sciatic nerve regeneration in rats

Peripheral nerve injuries can lead to sensory or motor deficits that have a serious impact on a patient's mental health and quality of life. Nevertheless, it remains a major clinical challenge to develop functional nerve conduits as an alternative to autologous grafts. We applied reduced graphene oxide (rGO) as a bioactive conductive material to impart electrophysiological properties to a 3D printed scaffold and the application of a pulsed magnetic field to excite the formation of microcurrents and induce nerve regeneration.In vitrostudies showed that the nerve scaffold and the pulsed magnetic field made no effect on cell survival, increased S-100βprotein expression, enhanced cell adhesion, and increased the expression level of nerve regeneration-related mRNAs.In vivoexperiments suggested that the protocol was effective in promoting nerve regeneration, resulting in functional recovery of sciatic nerves in rats, when they were damaged close to that of the autologous nerve graft, and increased expression of S-100β, NF200, and GAP43. These results indicate that rGO composite nerve scaffolds combined with pulsed magnetic field stimulation have great potential for peripheral nerve rehabilitation.

Lacosamide alleviates bilateral cavernous nerve injury-induced erectile dysfunction in the rat model by ameliorating pathological changes in the corpus cavernosum

Bilateral cavernous nerve injury-related erectile dysfunction (BCNI-ED) shows a limited response to type 5 phosphodiesterase inhibitors. Furthermore, lacosamide (LCM) can alleviate peripheral neuropathy. To explore whether LCM can improve the erectile response after BCNI, we randomly divided 30 young Sprague-Dawley rats into three groups (n = 10 per group), namely, the sham operation, 0.9% normal saline-treated (BCNI + 0.9% NS), and LCM-treated BCNI (BCNI + LCM) groups. LCM was injected intraperitoneally at a dose of 90 mg/kg/day for 7 consecutive days. Erectile function was assessed by measuring the ratio of peak intracavernous pressure (ICP) to mean arterial pressure (MAP), and tissues were harvested for transmission electron microscopy, immunofluorescence, Masson's trichrome staining, TUNEL staining, and Western blot analysis. The BCNI + 0.9% NS group showed reduced ICP/MAP ratio (0.93 ± 0.04 vs. 0.44 ± 0.05, P < 0.0001). An increased proportion of TUNEL-positive cells (0.04 ± 0.01 vs 0.87 ± 0.03, P < 0.0001) and a decreased smooth muscle/collagen ratio (0.44 ± 0.01 vs. 0.33 ± 0.01, P < 0.001) were observed in the BCNI + 0.9% NS compared with the sham group. Administration of LCM significantly restored the ICP/MAP ratio (0.44 ± 0.05 vs. 0.74 ± 0.05, P < 0.001) and decreased the proportion of TUNEL positive cells (0.87 ± 0.03 vs. 0.60 ± 0.04, P < 0.0001) in the corpus cavernosum following BCNI. The ratio of smooth muscle to collagen (0.43 ± 0.01vs. 0.33 ± 0.01, P < 0.01) and expression of α-SMA (P < 0.0001) in the BCNI + LCM group significantly increased compared with BCNI + 0.9% NS group, indicating alleviation of fibrosis. Apoptotic markers, including Bax/Bcl-2 (P < 0.01) and Caspase-3 (P < 0.0001) in the BCNI + LCM group was significantly lower than that in the BCNI + 0.9% NS group. LCM treatment partially upregulated the expression of vWF and eNOS in cavernous tissue in rats subjected to BCNI (P < 0.05). Increases in S100-β and nNOS expression in the major pelvic ganglion (MPG) were observed after LCM administration. In summary, LCM can recover erectile function in BCNI-ED rat model by suppressing corporal apoptosis and fibrosis, and protecting the cavernous nerve.

Electroactive scaffolds of biodegradable polyurethane/polydopamine-functionalized graphene oxide regulating the inflammatory response and revitalizing the axonal growth cone for peripheral nerve regeneration

Long-gap peripheral nerve injury remains a major challenge in regenerative medicine and results in permanent sensory and motor dysfunction. Nerve guidance scaffolds (NGSs) are known as a promising alternative to autologous nerve grafting. The latter, the current "gold standard" in clinical practice, is frequently constrained by the limited availability of sources and the inevitable damage to the donor area. Given the electrophysiological properties of nerves, electroactive biomaterials are being intensively investigated in nerve tissue engineering. In this study, we engineered a conductive NGS compounded of biodegradable waterborne polyurethane (WPU) and polydopamine-reduced graphene oxide (pGO) for repairing impaired peripheral nerves. The incorporation of pGO at the optimal concentration (3 wt%) promoted in vitro spreading of Schwann cells (SCs) with high expression of the proliferation marker S100 protein. In an in vivo study of sciatic nerve transection injury, WPU/pGO NGSs were found to regulate the immune microenvironment by activating macrophage M2 polarization and upregulate growth-associated protein 43 (GAP43) to facilitate axonal elongation. Histological and motor function analysis demonstrated that WPU/pGO NGSs had a neuroprosthetic effect close to that of an autograft, which significantly promoted the regeneration of myelinated axons, reduced gastrocnemius atrophy, and enhanced hindlimb motor function. These findings together suggested that electroactive WPU/pGO NGSs may represent a safe and effective strategy to manage large nerve defects.

THE EFFECTS OF CURCUMIN AND BLUEBERRY ON AXONAL REGENERATION AFTER PERIPHERAL NERVE INJURY

The purpose of this study was to analyze the axonal regeneration and therapeutic effects of curcumin and blueberry administration following peripheral nerve injury using stereological, electron microscopic and electrophysiological methods. Animals in were assigned into one of four groups - control (Cont), injury (Inj), injury+curcumin (Cur) and injury+blueberry (Blue). Following the induction of sciatic nerve crush injury (75 Newtons for 5sec) in the Inj, Cur, and Blue groups, the rats in the Cur group received intraperitoneal injection of 30mg/kg curcumin (Sigma C1386) and the rats in the Blue group received 4g/kg blueberry by gavage over a four-week period. The rats in the Cont and Inj groups were not exposed to any substance. All animals were given standard chow. Sciatic functional index analyses were performed on the 14^th and 28^th days after injury, and electromyography (EMG) results were recorded. Stereological analysis of the nerve was performed under light microscopy. Light and electron microscopies were used for the histopathological evaluation of the sciatic nerve. Analysis of myelinated axon numbers revealed no significant differences between the Inj group and the Cur and Blue groups. However, a significant difference was observed between the Blue and Inj groups in terms of axonal areas. EMG test results differed between the Blue and the Inj groups (p<0.05), but no significant difference was observed between the Inj and Cur groups. Electron microscopic analysis revealed protective effects of curcumin and blueberry treatment after injury. The use of the curcumin and blueberry may represent a supportive approach to the protection of nerve fibers after peripheral nerve crush injury.

The effect of tropisetron on peripheral diabetic neuropathy: possible protective actions against inflammation and apoptosis

Diabetic peripheral neuropathy (DPN) is a common nerve disorder of diabetes. The aim of this study was to explore the protective effects of tropisetron in DPN. Type 1 diabetes was created by a single injection of streptozotocin (50 mg/kg, ip). Tropisetron (3 mg/kg, ip) was administered daily for 2 weeks. Our analysis showed that nerve fibers and their myelin sheaths were thinned with decreased myelinated fiber number in diabetic animals. The intensity of Bcl-2 staining decreased and the intensity of Bax staining increased in the sciatic nerves of diabetic rats by using immunohistochemical staining. Furthermore, diabetes significantly increased tumor necrosis factor-alpha, interleukin 1-β (TNFα and IL-1β) and Bax/Bcl-2 ratio in sciatic nerves of rats. However, intraperitoneal injection of tropisetron significantly reversed these alterations induced by diabetes. These findings suggest that tropisetron attenuates diabetes-induced peripheral nerve injury through its anti-inflammatory and anti-apoptotic effects, and may provide a novel therapeutic strategy to ameliorate the process of peripheral neuropathy in diabetes.

The role of spinal cord tractography in detecting lesions following selective bladder afferent and efferent fibers: A novel method for induction of neurogenic lower urinary tract dysfunction in rabbit

OBJECTIVE

Neurogenic lower urinary tract dysfunction (NLUTD), a challenging disorder, is defined by lack of bladder control due to the abnormalities in neural pathways and can be classified based on the location of lesions within the nervous system, thus investigating the neural pathways can help us to know the site of the lesion and specify the class of the NLUTD. Diffusion Tensor Imaging (DTI) tractography, a noninvasive advanced imaging method, is capable of detecting central nervous system pathologies, even if routine magnetic resonance imaging shows no abnormality. Accordingly, tractography is an ideal technique to evaluate patients with NLUTD and visualize the pathology site within the spine. This study aimed to introduce a novel method of spinal cord injury (SCI) to establish NLUTD in the rabbit and to investigate the potential of tractography in tracing neural tracts of the spinal cord in an induced NLUTD animal model.

MATERIALS AND METHODS

An animal model of NLUTD was induced through cauterization of the spinal cord at the level T12-L1 in 12 rabbits. Then rabbits were assessed via DTI, urodynamic studies (UDS), voiding cystourethrogram (VCUG), and pathology assessments using antineurofilament 200 (NF200) antibody, anti-S100, anti-Smooth Muscle Actin, anti-Myogenin, and anti-MyoD1.

RESULTS

The tractography visualized lesions within spinal cord fibers. DTI parameters including fractional anisotropy (FA) value and tract density were significantly decreased (FA: p-value = 0.01, Tract density: p-value = 0.05) after injury. The mean diffusivity (MD) was insignificantly increased compared to before the injury. Also, the results of UDS and pathology assessments corroborated that applying SCI and the establishment of the NLUTD model was completely successful.

CONCLUSION

In the present study, we investigated the auxiliary role of tractography in detecting the spinal cord lesions in the novel established rabbit model of NLUTD. The introduced method of NLUTD induction was without the leg's neurological deficit, easily applicable, low-cost, and was accompanied by minimal surgical preparation and a satisfactory survival rate in comparison with other SCI animal models.

Ameliorating potential of curcumin and its analogue in central nervous system disorders and related conditions: A review of molecular pathways

Curcumin, isolated from turmeric (Curcuma longa L.) is one of the broadly studied phytomolecule owing to its strong antioxidant and anti-inflammatory potential and has been considered a promising therapeutic candidate in a wide range of disorders. Considering, its low bioavailability, different curcumin analogs have been developed to afford desired pharmacokinetic profile and therapeutic outcome in varied pathological states. Several preclinical and clinical studies have indicated that curcumin ameliorates mitochondrial dysfunction, inflammation, oxidative stress apoptosis-mediated neural cell degeneration and could effectively be utilized in the treatment of different neurodegenerative diseases. Hence, in this review, we have summarized key findings of experimental and clinical studies conducted on curcumin and its analogues with special emphasis on molecular pathways, viz. NF-kB, Nrf2-ARE, glial activation, apoptosis, angiogenesis, SOCS/JAK/STAT, PI3K/Akt, ERK1/2 /MyD88 /p38 MAPK, JNK, iNOS/NO, and MMP pathways involved in imparting ameliorative effects in the therapy of neurodegenerative disorders and associated conditions.

The Impact of Supplements on Recovery After Peripheral Nerve Injury: A Review of the Literature

Peripheral nerve injury (PNI) can result from trauma, surgical resection, iatrogenic injury, and/or local anesthetic toxicity. Damage to peripheral nerves may result in debilitating weakness, numbness, paresthesia, pain, and/or autonomic instability. As PNI is associated with inflammation and nerve degeneration, means to mitigate this response could result in improved outcomes. Numerous nutrients have been investigated to prevent the negative sequelae of PNI. Alpha-lipoic acid, cytidine diphosphate-choline (CDP Choline), curcumin, melatonin, vitamin B12, and vitamin E have demonstrated notable success in improving recovery following PNI within animal models. While animal studies show ample evidence that various supplements may improve recovery after PNI, similar evidence in human patients is limited. The goal of this review is to analyze supplements that have been used successfully in animal models of PNI to serve as a reference for future studies on human patients. By analyzing supplements that have shown efficacy in animal studies, healthcare providers will have a resource from which to guide decision-making regarding future human studies investigating the role that supplements could play in PNI recovery. Ultimately, establishing a comprehensive understanding of these supplements in human patients following PNI may significantly improve post-surgical outcomes, quality of life, and peripheral nerve regeneration.

The Potential Benefits of Dietary Polyphenols for Peripheral Nerve Regeneration

Peripheral nerves are frequently affected by lesions caused by trauma (work accidents, car incidents, combat injuries) and following surgical procedures (for instance cancer resection), resulting in loss of motor and sensory function with lifelong impairments. Irrespective of the intrinsic capability of the peripheral nervous system for regeneration, spontaneous or surgically supported regeneration is often unsatisfactory with the limited functional success of nerve repair. For this reason, many efforts have been made to improve the regeneration process. Beyond innovative microsurgical methods that, in certain cases, are necessary to repair nerve injuries, different nonsurgical treatment approaches and adjunctive therapies have been investigated to enhance nerve regeneration. One possibility could be taking advantage of a healthy diet or lifestyle and their relation with proper body functions. Over the years, scientific evidence has been obtained on the benefits of the intake of polyphenols or polyphenol-rich foods in humans, highlighting the neuroprotective effects of these compounds in many neurodegenerative diseases. In order to improve the available knowledge about the potential beneficial role of polyphenols in the process of peripheral nerve regeneration, this review assessed the biological effects of polyphenol administration in supporting and promoting the regenerative process after peripheral nerve injury.

An injectable and self-healing hydrogel with controlled release of curcumin to repair spinal cord injury

The harsh local micro-environment following spinal cord injury (SCI) remains a great challenge for neural regeneration. Local reconstitution of a favorable micro-environment by biocompatible scaffolds with desirable functions has thus been an area of concern. Herein, a hybrid hydrogel was developed using Fmoc-grafted chitosan (FC) and Fmoc peptide (FI). Dynamic reversible π-π stacking interactions of the fluorenyl rings enabled the FC/FI hybrid hydrogel to exhibit excellent injectable and self-healing properties, as characterized by visual appearances and rheological tests. Furthermore, the FC/FI hybrid hydrogel showed a slow and persistent release of curcumin (Cur), which was named as FC/FI-Cur hydrogel. In vitro studies confirmed that with the support of FC/FI-Cur hydrogel, neurite outgrowth was promoted, and Schwann cell (SC) migration away from dorsal root ganglia (DRG) spheres with enhanced myelination was substantiated. The FC/FI-Cur hydrogel well reassembled extracellular matrix at the lesion site of rat spinal cord and exerted outstanding effects in modulating local inflammatory reaction by regulating the phenotypes of infiltrated inflammatory cells. In addition, endogenous SCs were recruited in the FC/FI-Cur graft and participated in the remyelination process of the regenerated nerves. These outcomes favored functional recovery, as evidenced by improved hind limbs movement and enhanced electrophysiological properties. Thus, our study not only advanced the development of multifunctional hydrogels but also provided insights into comprehensive approaches for SCI repair.

Engineering 2D approaches fibrous platform incorporating turmeric and polyaniline nanoparticles to predict the expression of βIII-Tubulin and TREK-1 through qRT-PCR to detect neuronal differentiation of PC12 cells

The bioengineering electroactive construct of a nerve-guided conduit for repairing and restoring injured nerves is an exciting biomedical endeavor that has implications for the treatment of peripheral nerve injury. In this study, we report the development the polycaprolactone (PCL) nanofibrous substrate consisting of turmeric (TUR) and polyaniline nanoparticles (PANINPs) exhibits topological and biological features that mimics the natural extracellular matrix (ECM) for nerve cells. We evaluated the morphology of 2-dimensional (2D) fibrous substrates, and their ability of stem cell adhesion, growth and proliferation rate were influenced by use of various concentrations of turmeric in PCL-TUR substrates. The results showed that 0.62 wt% of TUR and 0.28 wt% of PANINPs in PCL nanofibers substrate exhibited the optimal cellular microenvironment to accelerate PC12 cellular activities. The in vitro experiments revealed that PCL-TUR@PANI substrates significantly stimulated the proliferation, differentiation, and spontaneous outgrowth and extension of neurites from the cells. The substrate has the capacity to respond directly to neuronal markers with significant upregulation of βIII-Tubulin and TREK-1 through myelination, and also trigger neurotrophic protein expression, which was confirmed via immunocytochemistry and quantitative real-time polymerase chain reaction (qRT-PCR) analysis. This study provides a new technique to design substrate of nerve tissue-specific microenvironment for peripheral nerve cell regeneration and could offer promising biomaterials for in vivo peripheral nerve repair.

Curcumin Can Activate the Nrf2/HO-1 Signaling Pathway and Scavenge Free Radicals in Spinal Cord Injury Treatment

Spinal cord injury (SCI) is a devastating event that often leads to permanent neurological deficits. Evidence from emerging studies has implicated oxygen-derived free radicals and high-energy oxidants as mediators of secondary SCI. Therefore, targeting these mediators using antioxidants could be beneficial for the disease. Several signaling pathways, such as the nuclear factor erythroid-2-related factor 2/heme oxygenase 1 (Nrf2/HO-1), have been associated with the regulation of some pathophysiological features of SCI. Curcumin is a plant medicinal agent whose diverse pharmacological properties have been extensively investigated and reported, notably its ability to curtail inflammatory damage by inhibiting the nuclear factor-κ-light-chain-enhancer of activated B cells. In this review, we analyze the role of curcumin in activating Nrf2/HO-1 and scavenging free radicals to repair SCI. With its minimal side effects, curcumin could be a potential therapy for SCI treatment.

Phagocytosis by Peripheral Glia: Importance for Nervous System Functions and Implications in Injury and Disease

The central nervous system (CNS) has very limited capacity to regenerate after traumatic injury or disease. In contrast, the peripheral nervous system (PNS) has far greater capacity for regeneration. This difference can be partly attributed to variances in glial-mediated functions, such as axon guidance, structural support, secretion of growth factors and phagocytic activity. Due to their growth-promoting characteristic, transplantation of PNS glia has been trialed for neural repair. After peripheral nerve injuries, Schwann cells (SCs, the main PNS glia) phagocytose myelin debris and attract macrophages to the injury site to aid in debris clearance. One peripheral nerve, the olfactory nerve, is unique in that it continuously regenerates throughout life. The olfactory nerve glia, olfactory ensheathing cells (OECs), are the primary phagocytes within this nerve, continuously clearing axonal debris arising from the normal regeneration of the nerve and after injury. In contrast to SCs, OECs do not appear to attract macrophages. SCs and OECs also respond to and phagocytose bacteria, a function likely critical for tackling microbial invasion of the CNS via peripheral nerves. However, phagocytosis is not always effective; inflammation, aging and/or genetic factors may contribute to compromised phagocytic activity. Here, we highlight the diverse roles of SCs and OECs with the focus on their phagocytic activity under physiological and pathological conditions. We also explore why understanding the contribution of peripheral glia phagocytosis may provide us with translational strategies for achieving axonal regeneration of the injured nervous system and potentially for the treatment of certain neurological diseases.

Effects of tamoxifen therapy on sciatic nerve crush injury: An experimental study in rats

OBJECTIVE

This study aimed to determine the effects of tamoxifen on sciatic nerve crush injury in a rat model using histopathological, histomorphometric, and immunohistochemical approaches.

METHODS

In this study, 24 male Sprague-Dawley rats aged of 5 to 7 weeks and weighing between 300 g and 400 g were used. The rats were randomly divided into 3 groups: control (group C), sciatic nerve injury (group SNI), and sciatic nerve injury with tamoxifen (group SNT). The sciatic nerve crush injury model was performed using the De Koning's crush force method. In group C, only a skin incision was made and then the skin was sutured. In group SNI, the injury model was performed but no treatment was applied. In group SNT, the injury model was executed, and then 40 mg/kg/day tamoxifen was given for 4 weeks by intraperitoneal methods. At the end of 4 weeks, all animals were killed using high doses of an anesthetic. Approximately, 2-cm sciatic nerve samples were obtained for histopathological, histomorphometric, and immunohistochemical analyses using the old skin incision.

RESULTS

In the histopathological examination, vascular congestion and density of vacuolization were significantly lower in group SNT than in group SNI (p<0.05). In the histomorphometric examination, the mean sciatic nerve diameter was 306±62 µm in group C, 510±42 µm in group SNI, and 204±23 µm in group SNT. A significant difference was observed in the sciatic nerve diameter measurements among the 3 groups (p<0.05). In pairwise comparisons, the mean sciatic nerve diameter was significantly lower in group SNT than in group SNI (p=0.00002). Sciatic nerve diameter measurements of both groups were found to be significantly higher than group C (p<0.05). The mean epineurium thickness was 17±0.8 µm in group C, 32±2.5 µm in group SNI, and 17±0.8 µm in group SNT. A significant difference was observed in the epineurium thickness measurements among the 3 groups (p<0.05). In pairwise comparisons, the epineurium thickness was significantly higher in group SNI than in groups SNT and C (p<0.05). In the immunohistochemical analysis, S100 immunoreactivity was found significantly higher in group SNI than in the other 2 groups (p<0.05).

CONCLUSION

The histomorphometric, histopathological, and immunohistochemical data obtained from this study have shown that tamoxifen has a beneficial effect on sciatic nerve crush injury in the experimental rat model.

Ascorbic acid accelerates Wallerian degeneration after peripheral nerve injury

Wallerian degeneration occurs after peripheral nerve injury and provides a beneficial microenvironment for nerve regeneration. Our previous study demonstrated that ascorbic acid promotes peripheral nerve regeneration, possibly through promoting Schwann cell proliferation and phagocytosis and enhancing macrophage proliferation, migration, and phagocytosis. Because Schwann cells and macrophages are the main cells involved in Wallerian degeneration, we speculated that ascorbic acid may accelerate this degenerative process. To test this hypothesis, 400 mg/kg ascorbic acid was administered intragastrically immediately after sciatic nerve transection, and 200 mg/kg ascorbic acid was then administered intragastrically every day. In addition, rat sciatic nerve explants were treated with 200 μM ascorbic acid. Ascorbic acid significantly accelerated the degradation of myelin basic protein-positive myelin and neurofilament 200-positive axons in both the transected nerves and nerve explants. Furthermore, ascorbic acid inhibited myelin-associated glycoprotein expression, increased c-Jun expression in Schwann cells, and increased both the number of macrophages and the amount of myelin fragments in the macrophages. These findings suggest that ascorbic acid accelerates Wallerian degeneration by accelerating the degeneration of axons and myelin in the injured nerve, promoting the dedifferentiation of Schwann cells, and enhancing macrophage recruitment and phagocytosis. The study was approved by the Southern Medical University Animal Care and Use Committee (approval No. SMU-L2015081) on October 15, 2015.

Key Developments in the Potential of Curcumin for the Treatment of Peripheral Neuropathies

Peripheral neuropathies (PN) can be triggered after metabolic diseases, traumatic peripheral nerve injury, genetic mutations, toxic substances, and/or inflammation. PN is a major clinical problem, affecting many patients and with few effective therapeutics. Recently, interest in natural dietary compounds, such as polyphenols, in human health has led to a great deal of research, especially in PN. Curcumin is a polyphenol extracted from the root of Curcuma longa. This molecule has long been used in Asian medicine for its anti-inflammatory, antibacterial, and antioxidant properties. However, like numerous polyphenols, curcumin has a very low bioavailability and a very fast metabolism. This review addresses multiple aspects of curcumin in PN, including bioavailability issues, new formulations, observations in animal behavioral tests, electrophysiological, histological, and molecular aspects, and clinical trials published to date. The, review covers in vitro and in vivo studies, with a special focus on the molecular mechanisms of curcumin (anti-inflammatory, antioxidant, anti-endoplasmic reticulum stress (anti-ER-stress), neuroprotection, and glial protection). This review provides for the first time an overview of curcumin in the treatment of PN. Finally, because PN are associated with numerous pathologies (e.g., cancers, diabetes, addiction, inflammatory disease...), this review is likely to interest a large audience.

Current Status of Therapeutic Approaches against Peripheral Nerve Injuries: A Detailed Story from Injury to Recovery

Peripheral nerve injury is a complex condition with a variety of signs and symptoms such as numbness, tingling, jabbing, throbbing, burning or sharp pain. Peripheral nerves are fragile in nature and can easily get damaged due to acute compression or trauma which may lead to the sensory and motor functions deficits and even lifelong disability. After lesion, the neuronal cell body becomes disconnected from the axon's distal portion to the injury site leading to the axonal degeneration and dismantlement of neuromuscular junctions of targeted muscles. In spite of extensive research on this aspect, complete functional recovery still remains a challenge to be resolved. This review highlights detailed pathophysiological events after an injury to a peripheral nerve and the associated factors that can either hinder or promote the regenerative machinery. In addition, it throws light on the available therapeutic strategies including supporting therapies, surgical and non-surgical interventions to ameliorate the axonal regeneration, neuronal survival, and reinnervation of peripheral targets. Despite the availability of various treatment options, we are still lacking the optimal treatments for a perfect and complete functional regain. The need for the present age is to discover or design such potent compounds that would be able to execute the complete functional retrieval. In this regard, plant-derived compounds are getting more attention and several recent reports validate their remedial effects. A plethora of plants and plant-derived phytochemicals have been suggested with curative effects against a number of diseases in general and neuronal injury in particular. They can be a ray of hope for the suffering individuals.

Comparison of melatonin and curcumin effect at the light and dark periods on regeneration of sciatic nerve crush injury in rats

Being one of the acute clinical problems, peripheral nerve injury can bring about a number of consequences including severe disability, reduced Quality of life (QOL) and immense costs. Currently, melatonin and curcumin are widely applied because of their immunomodulatory, anti-inflammatory, neuro-protective and antioxidant properties. The present study aims to compare the effects of melatonin and curcumin during light and dark periods on sciatic nerve crush injury repair. Accordingly, rats received IP injections of curcumin (100 mg/kg) and melatonin (10 mg/kg) over two periods of light (9:00 a.m.) and dark (9:00 p.m.) for 4 weeks. In order to evaluate rats, functional (walking track analysis and electrophysiological measurements), histomorphometric and gastrocnemius muscle mass investigations were administered. No statistically significant difference was identified between dark and light curcumin groups while curcumin groups displayed better results than did melatonin groups. In addition, dark melatonin group displayed better results than the light melatonin. On the whole, this study found that melatonin and curcumin can be used to quicken neural recovery and help treat nerve injury. It was also found that better neuroregeneration or nerve regeneration was induced when rats were treated by melatonin during the dark period while effects and injection time did not correlate in curcumin application.

Ascorbic Acid Facilitates Neural Regeneration After Sciatic Nerve Crush Injury

Ascorbic acid (AA) is an essential micronutrient that has been safely used in the clinic for many years. The present study indicates that AA has an unexpected function in facilitating nerve regeneration. Using a mouse model of sciatic nerve crush injury, we found that AA can significantly accelerate axonal regrowth in the early stage [3 days post-injury (dpi)], a finding that was revealed by immunostaining and Western blotting for antibodies against GAP-43 and SCG10. On day 28 post-injury, histomorphometric assessments demonstrated that AA treatment increased the density, size, and remyelination of regenerated axons in the injured nerve and alleviated myoatrophy in the gastrocnemius. Moreover, the results from various behavioral tests and electrophysiological assays revealed that nerve injury-derived functional defects in motor and sensory behavior as well as in nerve conduction were significantly attenuated by treatment with AA. The potential mechanisms of AA in nerve regeneration were further explored by investigating the effects of AA on three types of cells involved in this process [neurons, Schwann cells (SCs) and macrophages] through a series of experiments. Overall, the data illustrated that AA treatment in cultured dorsal root ganglionic neurons resulted in increased neurite growth and lower expression of RhoA, which is an important inhibitory factor in neural regeneration. In SCs, proliferation, phagocytosis, and neurotrophin expression were all enhanced by AA. Meanwhile, AA treatment also improved proliferation, migration, phagocytosis, and anti-inflammatory polarization in macrophages. In conclusion, this study demonstrated that treatment with AA can promote the morphological and functional recovery of injured peripheral nerves and that this effect is potentially due to AA’s bioeffects on neurons, SCs and macrophages, three of most important types of cells involved in nerve injury and regeneration.

Local low dose curcumin treatment improves functional recovery and remyelination in a rat model of sciatic nerve crush through inhibition of oxidative stress

Traumatic injuries to peripheral nerves are frequent, however, specific pharmacological treatments are currently lacking. Curcumin has antioxidant, anti-inflammatory and neuroprotective properties but high oral doses are required for therapeutic use, particularly due to its low bioavailability. The aim of the present study was to investigate the effects of local and continuous treatment using low curcumin doses on functional recovery and nerve regeneration after rat sciatic nerve crush (SNC). Curcumin was administered by osmotic pumps with a catheter delivering the drug at the injury site (0.2 mg/day for 4 weeks). Functionally, early improvements in mechanical sensitivity, finger spacing of the injured paw, skilful walking and grip strength were observed in curcumin-treated animals. The curcumin treatment increased expression of compact myelin proteins (MPZ and PMP22), myelin sheath thickness and, correspondingly, increased motor and sensitive nerve conduction velocity. Microscopic analysis of gastrocnemius muscle indicated a curcumin-induced decrease in neurogenic lesions. Curcumin treatment reduced the production of reactive oxygen species (ROS) (which were notably produced by macrophages), lipid peroxidation and increased expression of transcription factor Nrf2. In silico analyses indicated that curcumin combines all the characteristics required to be an efficient lipid peroxidation inhibitor at the heart of biological membranes, hence protecting their degradation due to ROS. This antioxidant capacity is likely to contribute to the beneficial effects of curcumin after SNC injury. These results demonstrate that, when administrated locally, low doses of curcumin represent a promising therapy for peripheral nerve regeneration.