Neurotropin® Accelerates the Differentiation of Schwann Cells and Remyelination in a Rat Lysophosphatidylcholine-Induced Demyelination Model

Region-specific response of central microglial cells to sciatic nerve demyelination through sensory and motor pathways

Peripheral nerve injury can cause changes in microglial cells on the spinal dorsal and ventral horns. This region-specific response implies that central microglial cells could be activated through both sensory and motor pathways. In order to further determine how peripheral nerve injury activates central microglial cells through neural pathways, the sciatic nerve was selected as the target for neural tract tracing and demyelination. Firstly, we used cholera toxin subunit B (CTB) to map the central sensory and motor territories of the sciatic nerve. Secondly, we applied lysophosphatidylcholine to establish the model of sciatic nerve demyelination and examined the distribution of activated microglial cells via immunofluorescence with ionized calcium-binding adapter molecule 1. It was shown that CTB labeling included the transganglionically labeled sensory afferents and retrogradely labeled somata of motor neurons along the sensory and motor pathways of the sciatic nerve ipsilateral to the injection, in which sensory afferents terminated on the gracile nucleus, Clarke's nucleus, and spinal dorsal horn, while motor neurons located on the spinal ventral horn. Consistently, after sciatic nerve demyelination, the activated microglial cells were observed in the same territories as CTB-labeling, showing shortened processes and enlarged cell bodies. These results support the idea that central microglia might be activated by signals from the demyelinated sciatic nerve through both sensory and motor pathways.

In vitro models for neuropathic pain phenotypic screening in brain therapeutics

The discovery of brain therapeutics faces a significant challenge due to the low translatability of preclinical results into clinical success. To address this gap, several efforts have been made to obtain more translatable neuronal models for phenotypic screening. These models allow the selection of active compounds without predetermined knowledge of drug targets. In this review, we present an overview of various existing models within the field, examining their strengths and limitations, particularly in the context of neuropathic pain research. We illustrate the usefulness of these models through a comparative review in three crucial areas: i) the development of novel phenotypic screening strategies specifically for neuropathic pain, ii) the validation of the models for both primary and secondary screening assays, and iii) the use of the models in target deconvolution processes.

Neurotropin® accelerates peripheral nerve regeneration in a rat sciatic nerve crush injury model

BACKGROUND

Peripheral nerve injuries are common and serious conditions. The effect of Neurotropin® (NTP), a nonprotein extract derived from the inflamed skin of rabbits inoculated with vaccinia virus, on peripheral nerve regeneration has not been fully elucidated. However, it has analgesic properties via the activation of descending pain inhibitory systems. Therefore, the current study aimed to determine the effects of NTP on peripheral nerve regeneration.

METHODS

We examined axonal outgrowth of dorsal root ganglion (DRG) neurons using immunocytochemistry in vitro. In addition, nerve regeneration was evaluated functionally, electrophysiologically, and histologically in a rat sciatic nerve crush injury model in vivo. Furthermore, gene expression of neurotrophic factors in the injured sciatic nerves and DRGs was evaluated.

RESULTS

In the dorsal root ganglion neurons in vitro, NTP promoted axonal outgrowth at a concentration of 10 mNU/mL. Moreover, the systemic administration of NTP contributed to the recovery of motor and sensory function at 2 weeks, and of sensory function, nerve conduction velocity, terminal latency, and axon-remyelination 4 weeks after sciatic nerve injury. In the gene expression assessment, insulin-like growth factor 1 and vascular endothelial growth factor expressions were increased in the injured sciatic nerve 2 days postoperatively.

CONCLUSIONS

Therefore, NTP might be effective in not only treating chronic pain but also promoting peripheral nerve regeneration after injury.

Exercise induced myelin protein zero improvement in neuropathic pain rats

PURPOSE

Aerobic exercise including swimming plays a suitable role in improving somatosensory injuries. Neuropathic pain is a debilitating condition that occurs following injury or diseases of somatosensory system. In the present study, we tried to investigate the effect of exercise on myelin protein zero of sciatic nerve injured rats.

MATERIALS AND METHODS

Forty male rats (180-220 g) were divided into five groups (intact, sham, sham + exercise, neuropathy, and neuropathy + exercise). Right Sciatic nerve of anesthetized rats was exposed and loosely ligated (four ligations with 1 mm apart) using catgut chromic sutures to induce neuropathy. After 3 days of recovery, swimming exercise began (20 min/day/5 days a week/4 weeks). Mechanical allodynia and thermal hyperalgesia were detected using Von Frey filaments and plantar test, respectively. Sciatic nerve at the place of injury was dissected out to measure the myelin protein zero by western blot analysis. In the intact and sham groups, sciatic nerve removed at the place similar to injured group.

RESULTS

We found that neuropathy significantly (p < 0.05) reduced paw withdrawal mechanical and thermal thresholds and swimming exercise significantly (p < 0.05) increased paw withdrawal mechanical and thermal thresholds compared to the neuropathy group. Moreover, we found that MPZ level significantly (p < 0.01) decreased in neuropathy group against that in sham group, and exercise prominently (p < 0.05) reversed MPZ level towards control level.

CONCLUSIONS

Swimming exercise improves myelin protein zero level in neuropathic rats along with attenuating neuropathic pain. This is a promising approach in improving neuropathological disorders including Charcot-Marie-Tooth and Dejerine-Sottas disease.

Lysophosphatidylcholine: Potential Target for the Treatment of Chronic Pain

The bioactive lipid lysophosphatidylcholine (LPC), a major phospholipid component of oxidized low-density lipoprotein (Ox-LDL), originates from the cleavage of phosphatidylcholine by phospholipase A2 (PLA2) and is catabolized to other substances by different enzymatic pathways. LPC exerts pleiotropic effects mediated by its receptors, G protein-coupled signaling receptors, Toll-like receptors, and ion channels to activate several second messengers. Lysophosphatidylcholine (LPC) is increasingly considered a key marker/factor positively in pathological states, especially inflammation and atherosclerosis development. Current studies have indicated that the injury of nervous tissues promotes oxidative stress and lipid peroxidation, as well as excessive accumulation of LPC, enhancing the membrane hyperexcitability to induce chronic pain, which may be recognized as one of the hallmarks of chronic pain. However, findings from lipidomic studies of LPC have been lacking in the context of chronic pain. In this review, we focus in some detail on LPC sources, biochemical pathways, and the signal-transduction system. Moreover, we outline the detection methods of LPC for accurate analysis of each individual LPC species and reveal the pathophysiological implication of LPC in chronic pain, which makes it an interesting target for biomarkers and the development of medicine regarding chronic pain.

Construction and effect evaluation of different sciatic nerve injury models in rats

Background

The most commonly used experimental model for preclinical studies on peripheral nerve regeneration is the sciatic nerve injury model. However, no experimental study has been conducted to evaluate acute injury modes at the same time.

Objective

We conducted sciatic nerve transverse injury, clamp injury, keep epineurium and axon cutting injury, and chemical damage injury in rats to evaluate the degree of damage of the four different injury modes and the degree of self-repair after injury.

Methods

The sciatic nerve transverse injury model, clamp injury model, keep epineurium injury model, and chemical damage injury model were constructed. Then, the sciatic nerve function was assessed using clinical evaluation methods and electrophysiological examinations, as well as immunofluorescence and axonal counting assessments of the reconstructed nerve pathways.

Results

The evaluations showed that the transverse group had the lowest muscle action potential, sciatic functional index, nociceptive threshold, mechanical threshold, rate of wet gastrocnemius muscle weight, area of muscle fiber, and numbers of myelinated nerve fibers. The chemical group had the highest, while the clamp group and the keep epineurium group had medium.

Conclusion

Transverse injury models have the most stable effect among all damage models; chemical injury models self-recover quickly and damage incompletely with poor stability of effect; and clamp injury models and keep epineurium injury models have no significant differences in many ways with medium stability.

Fluorocitrate and neurotropin confer analgesic effects on neuropathic pain in diabetic rats via inhibition of astrocyte activation in the periaqueductal gray

Currently, effective treatments for diabetic neuropathic pain (DNP) are still unmet clinical needs. Activation of astrocytes in the ventrolateral region of periaqueductal gray (vlPAG) has a regulating effect on pain responses. The present study was designed to confirm that repeated intra-vlPAG injection of fluorocitrate (FC), a selective inhibitor of astrocyte activation or intraperitoneal (IP) injection of neurotropin, a widely prescribed analgesic drug for chronic pain, inhibited the activation of astrocytes in vlPAG and thus produced an analgesic effect on DNP. An in vivo model was developed to study DNP in rats. The changes in mechanical withdrawal threshold (MWT) and activation levels of astrocytes in the vlPAG were evaluated in all experimental rats. Compared with normal rats, vlPAG-based glial fibrillary acid protein (GFAP) was clearly upregulated, whereas the MWTs of DNP rats were markedly diminished. The intra-vlPAG injections of FC or IP injections of neurotropin attenuated the alterations both in MWTs and expression levels of GFAP in vlPAG in DNP rats. Collectively, these findings suggest the antinociceptive effects of FC and neurotropin in DNP rats, which were associated with suppressing the activation of astrocytes in vlPAG.

Neurotropin protects rotator cuff tendon cells from lidocaine-induced cell death

Background

Local anesthetics often are used in rotator cuff tears as therapeutic tools, although some cases have reported that they have detrimental effects. Neurotropin (NTP) is used widely in Japan as a treatment for various chronic pain conditions and is shown to have protective effects on cartilage and nerve cells. In this study, we investigated the protective effect of NTP against lidocaine-induced cytotoxicity.

Methods

Tenocytes from rotator cuff tendons were incubated with lidocaine, NTP, lidocaine with NTP, and a control medium. Cell viability was evaluated using the WST-8 assay. Cell apoptosis was detected via annexin V staining using flow cytometry. The expression of BCL-2 and cytochrome c, which are involved in the intrinsic mitochondrial pathway of apoptosis, was evaluated via Western blotting and immunohistochemical staining.

Results

In the cell viability assay, lidocaine decreased cell viability in a dose-dependent manner, and NTP did not affect cell viability. Moreover, NTP significantly inhibited the cytotoxic effect of lidocaine. The flow cytometry analysis showed that lidocaine significantly induced apoptosis in tenocytes, and NTP considerably inhibited this lidocaine-induced apoptosis. Western blotting experiments showed that lidocaine decreased the protein expression of BCL-2, and that NTP conserved the expression of BCL-2, even when used with lidocaine. Immunohistochemical staining for cytochrome c showed that 0.1% lidocaine increased cytochrome c-positive cells, and NTP suppressed lidocaine-induced cytochrome c expression.

Conclusions

NTP suppresses lidocaine-induced apoptosis of tenocytes by inhibiting the mitochondrial apoptotic pathway. Intra-articular/ bursal injection of NTP with lidocaine could protect tenocytes in rotator cuff tendons against lidocaine-induced apoptosis.

Effect of Interleukin-1β on Gene Expression Signatures in Schwann Cells Associated with Neuropathic Pain

Interleukin-1β (IL-1β) plays a critical role in the development of neuropathic pain through activation of Schwann cells (SCs) after nerve injury. Here, we applied an RNA sequencing (RNA-seq) approach to identify the effect of IL-1β on gene signatures of a rat SC line (RSC96) and the potential molecular mechanisms underlying the development of neuropathic pain. RNA-seq data demonstrated a total of 57 significantly differentially expressed genes (DEGs) with 35 up-regulated and 22 down-regulated between SCs treated with IL-1β, and control SCs without treatment. Bioinformatics analysis showed that key upregulated DEGs included those associated with immune and inflammation-related processes, neurotrophin production and SC proliferation. Five proteins encoded by key upregulated DEGs (Ceacam1, Hap1, Irs3, Lgi4 and Mif) were further verified by Western blot. Consistent with the RNA-Seq results, the expression of key genes was confirmed in SCs by immunofluorescence of the chronic constriction injury (CCI) sciatic nerve in rats. Furthermore, we demonstrated that treatment with IL-1β resulted in an increase in p38/ERK phosphorylation, and activators of p38/ERK enhanced the effect of IL-1β on the expression some of the key genes, whereas p38/ERK inhibitors reversed these effects. In conclusion, the present study highlights key genes involved in the development of neuropathic pain through activation of SCs after nerve injury. Identification of these genes and subsequent evidence of their mediation by IL-1β treatment promote our understanding of molecular mechanisms of nerve injury induced neuropathic pain, and highlight potential molecular targets for the treatment of neuropathic pain.

Negative Pressure Neurogenesis: A Novel Approach to Accelerate Nerve Regeneration after Complete Peripheral Nerve Transection

Various modalities to facilitate nerve regeneration have been described in the literature with limited success. We hypothesized that negative pressure applied to a sectioned peripheral nerve would enhance nerve regeneration by promoting angiogenesis and axonal lengthening.

METHODS

Wistar rats' sciatic nerves were cut (creating ~7 mm nerve gap) and placed into a silicone T-tube, to which negative pressure was applied. The rats were divided into 4 groups: control (no pressure), group A (low pressure: 10 mm Hg), group B (medium pressure: 20/30 mm Hg) and group C (high pressure: 50/70 mm Hg). The nerve segments were retrieved after 7 days for gross and histological analysis.

RESULTS

In total, 22 rats completed the study. The control group showed insignificant nerve growth, whereas the 3 negative pressure groups showed nerve growth and nerve gap reduction. The true nerve growth was highest in group A (median: 3.54 mm) compared to group B, C, and control (medians: 1.19 mm, 1.3 mm, and 0.35 mm); however, only group A was found to be significantly different to the control group (**P < 0.01). Similarly, angiogenesis was observed to be significantly greater in group A (**P < 0.01) in comparison to the control.

CONCLUSIONS

Negative pressure stimulated nerve lengthening and angiogenesis within an in vivo rat model. Low negative pressure (10 mm Hg) provided superior results over the higher negative pressure groups and the control, favoring axonal growth. Further studies are required with greater number of rats and longer recovery time to assess the functional outcome.

Association of NAT2 genetic polymorphism with the efficacy of Neurotropin® for the enhancement of aggrecan gene expression in nucleus pulposus cells: a pilot study

BACKGROUND

Intervertebral disc degeneration, one of the major causes of low-back pain, results from altered biosynthesis/turnover of extracellular matrix in the disc. Previously, we reported that the analgesic drug Neurotropin® (NTP) had an anabolic effect on glycosaminoglycan synthesis in cultured nucleus pulposus (NP) cells via the stimulation of chondroitin sulfate N-acetylgalactosaminyltransferase 1. However, its effect on the aggrecan core protein was not significantly detected, because of the data variance. A microarray analysis suggested that the effect of NTP on aggrecan was correlated with N-acetyltransferase 2 (NAT2), a drug-metabolizing enzyme. Specific NAT2 alleles are known to correlate with rapid, intermediate, and slow acetylation activities and side effects of various drugs. We investigated the association between the efficacy of NTP on aggrecan expression and the NAT2 genotype in cell donors.

METHODS

NP cells were isolated from intervertebral disc tissues donated by 31 Japanese patients (28-68 years) who underwent discectomy. NTP was added to the primary cell cultures and its effect on the aggrecan mRNA was analyzed using real-time quantitative PCR. To assess acetylator status, genotyping was performed based on the inferred NAT2 haplotypes of five common single-nucleotide polymorphisms using allele-specific PCR.

RESULTS

The phenotype frequencies of NAT2 in the patients were 0%, 42.0%, and 58.0% for slow, intermediate, and rapid acetylators, respectively. The proportions of responders to NTP treatment (aggrecan upregulation, ≥ 1.1-fold) in the intermediate and rapid acetylators were 76.9% and 38.9%, respectively. The odds ratio of the comparison of the intermediate acetylator status between responders and nonresponders was 5.2 (95% CI 1.06-26.0, P = 0.036), and regarding the 19 male patients, this was 14.0 (95% CI 1.54-127.2, P = 0.012). In the 12 females, the effect was not correlated with NAT2 phenotype but seemed to become weaker along with aging.

CONCLUSIONS

An intermediate acetylator status significantly favored the efficacy of NTP treatment to enhance aggrecan production in NP cells. In males, this tendency was detected with higher significance. This study provides suggestive data of the association between NAT2 variants and the efficacy of NTP treatment. Given the small sample size, results should be further confirmed.

Neuroprotection by Neurotropin through Crosstalk of Neurotrophic and Innate Immune Receptors in PC12 Cells

Infected or damaged tissues release multiple “alert” molecules such as alarmins and damage-associated molecular patterns (DAMPs) that are recognized by innate immune receptors, and induce tissue inflammation, regeneration, and repair. Recently, an extract from inflamed rabbit skin inoculated with vaccinia virus (Neurotropin^®, NTP) was found to induce infarct tolerance in mice receiving permanent ischemic attack to the middle cerebral artery. Likewise, we report herein that NTP prevented the neurite retraction in PC12 cells by nerve growth factor (NGF) deprivation. This effect was accompanied by interaction of Fyn with high-affinity NGF receptor TrkA. Sucrose density gradient subcellular fractionation of NTP-treated cells showed heretofore unidentified membrane fractions with a high-buoyant density containing Trk, B subunit of cholera toxin-bound ganglioside, flotillin-1 and Fyn. Additionally, these new membrane fractions also contained Toll-like receptor 4 (TLR4). Inhibition of TLR4 function by TAK-242 prevented the formation of these unidentified membrane fractions and suppressed neuroprotection by NTP. These observations indicate that NTP controls TrkA-mediated signaling through the formation of clusters of new membrane microdomains, thus providing a platform for crosstalk between neurotrophic and innate immune receptors. Neuroprotective mechanisms through the interaction with innate immune systems may provide novel mechanism for neuroprotection.

Neurotropin Inhibits Lipid Accumulation by Maintaining Mitochondrial Function in Hepatocytes via AMPK Activation

The accumulation of lipid droplets in the cytoplasm of hepatocytes, known as hepatic steatosis, is a hallmark of non-alcoholic fatty liver disease (NAFLD). Inhibiting hepatic steatosis is suggested to be a therapeutic strategy for NAFLD. The present study investigated the actions of Neurotropin (NTP), a drug used for chronic pain in Japan and China, on lipid accumulation in hepatocytes as a possible treatment for NAFLD. NTP inhibited lipid accumulation induced by palmitate and linoleate, the two major hepatotoxic free fatty acids found in NAFLD livers. An RNA sequencing analysis revealed that NTP altered the expression of mitochondrial genes. NTP ameliorated palmitate-and linoleate-induced mitochondrial dysfunction by reversing mitochondrial membrane potential, respiration, and β-oxidation, suppressing mitochondrial oxidative stress, and enhancing mitochondrial turnover. Moreover, NTP increased the phosphorylation of AMPK, a critical factor in the regulation of mitochondrial function, and induced PGC-1β expression. Inhibition of AMPK activity and PGC-1β expression diminished the anti-steatotic effect of NTP in hepatocytes. JNK inhibition could also be associated with NTP-mediated inhibition of lipid accumulation, but we did not find the association between AMPK and JNK. These results suggest that NTP inhibits lipid accumulation by maintaining mitochondrial function in hepatocytes via AMPK activation, or by inhibiting JNK.

Effect of the combination of high-frequency repetitive magnetic stimulation and neurotropin on injured sciatic nerve regeneration in rats

Repetitive magnetic stimulation is effective for treating posttraumatic neuropathies following spinal or axonal injury. Neurotropin is a potential treatment for nerve injuries like demyelinating diseases. This study sought to observe the effects of high-frequency repetitive magnetic stimulation, neurotropin and their combined use in the treatment of peripheral nerve injury in 32 adult male Sprague-Dawley rats. To create a sciatic nerve injury model, a 10 mm-nerve segment of the left sciatic nerve was cut and rotated through 180° and each end restored continuously with interrupted sutures. The rats were randomly divided into four groups. The control group received only a reversed autograft in the left sciatic nerve with no treatment. In the high-frequency repetitive magnetic stimulation group, peripheral high-frequency repetitive magnetic stimulation treatment (20 Hz, 20 min/d) was delivered for 10 consecutive days after auto-grafting. In the neurotropin group, neurotropin therapy (0.96 NU/kg per day) was administrated for 10 consecutive days after surgery. In the combined group, the combination of peripheral high-frequency repetitive magnetic stimulation (20 Hz, 20 min/d) and neurotropin (0.96 NU/kg per day) was given for 10 consecutive days after the operation. The Basso-Beattie-Bresnahan locomotor rating scale was used to assess the behavioral recovery of the injured nerve. The sciatic functional index was used to evaluate the recovery of motor functions. Toluidine blue staining was performed to determine the number of myelinated fibers in the distal and proximal grafts. Immunohistochemistry staining was used to detect the length of axons marked by neurofilament 200. Our results reveal that the Basso-Beattie-Bresnahan locomotor rating scale scores, sciatic functional index, the number of myelinated fibers in distal and proximal grafts were higher and axon lengths were longer in the high-frequency repetitive magnetic stimulation, neurotropin and combined groups compared with the control group. These measures were not significantly different among the high-frequency repetitive magnetic stimulation, neurotropin and combined groups. Therefore, our results suggest that peripheral high-frequency repetitive magnetic stimulation or neurotropin can promote the repair of injured sciatic nerves, but their combined use seems to offer no significant advantage. This study was approved by the Animal Ethics Committee of the Affiliated Changzhou No. 2 People’s Hospital of Nanjing Medical University, China on December 23, 2014 (approval No. 2014keyan002-01).

Lysophosphatidic acids and their substrate lysophospholipids in cerebrospinal fluid as objective biomarkers for evaluating the severity of lumbar spinal stenosis

Lysophospholipids (LPLs) are known to have potentially important roles in the initiation and maintenance of neuropathic pain in animal models. This study investigated the association between the clinical severity of lumbar spinal stenosis (LSS) and the cerebrospinal fluid (CSF) levels of LPLs, using human samples. We prospectively identified twenty-eight patients with LSS and fifteen controls with idiopathic scoliosis or bladder cancer without neurological symptoms. We quantified LPLs from CSF using liquid chromatography-tandem mass spectrometry. We assessed clinical outcome measures of LSS (Neuropathic Pain Symptom Inventory (NPSI) and Zurich Claudication Questionnaire (ZCQ)) and categorized patients into two groups according to their severity. Five species of lysophosphatidic acid (LPA), nine species of lysophosphatidylcholine (LPC), and one species of lysophosphatidylinositol (LPI) were detected. The CSF levels of all species of LPLs were significantly higher in LSS patients than controls. Patients in the severe NPSI group had significantly higher LPL levels (three species of LPA and nine species of LPC) than the mild group. Patients in the severe ZCQ group also had significantly higher LPL levels (four species of LPA and nine species of LPC). This investigation demonstrates a positive correlation between the CSF levels of LPLs and the clinical severity of LSS. LPLs are potential biomarkers for evaluating the severity of LSS.

Neurotropin reduces memory impairment and neuroinflammation via BDNF/NF-κB in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease with limited treatments and no cure. Neurotropin (NTP) is an analgesic drug widely prescribed for neuropathic pain. Increasing evidence suggests that NTP may also protect against neurodegeneration, but NTP's treatment potential against memory impairments of AD remains to be explored. APP/PS1 mice, which model AD, were given NTP for three months then cognitively tested with the Morris water maze. Their Aβ burden, microglial and astrocytic activation, and BDNF levels were compared to untreated controls using immunofluorescent staining. Expression of pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) and NF-κB pathway related proteins (p65 and IκB-α) were examined by ELISA or Western blots in vivo and in vitro in the microglia cell line. Lastly, BV-2 cells were pre-treated with the selective BDNF inhibitor ANA-12 and with NTP to examine mechanistic pathways. Taken together, NTP treatment reduced cognitive impairment, Aβ deposits, and glial activation in cortex and hippocampus APP/PS1 mice. IL-1β, IL-6 and TNF-α also decreased after NTP treatment in vivo and in vitro, and BDNF levels rose. Also, NTP reduced p65 and IκB-α activation and the effect of NTP on pro-inflammatory cytokines and NF-κB pathway related proteins was abolished by BDNF inhibitor. Our results indicate that NTP reduces neuroinflammation and improves the cognitive deficits in APP/PS1 mice possibly via BDNF/NF-κB pathway. NTP may be a new promising drug candidate for patients with AD.