Inhibition of IL-6 signaling: A novel therapeutic approach to treating spinal cord injury pain

Interleukin-6 in Spinal Cord Injury: Could Immunomodulation Replace Immunosuppression in the Management of Acute Traumatic Spinal Cord Injuries?

Traumatic spinal cord injuries (SCI) result in devastating impairment to an individual's functional ability. The pathophysiology of SCI is related to primary injury but further propagated by secondary reactions to injury, such as inflammation and oxidation. The inflammatory and oxidative cascades ultimately cause demyelination and Wallerian degeneration. Currently, no treatments are available to treat primary or secondary injury in SCI, but some studies have shown promising results by lessening secondary mechanisms of injury. Interleukins (ILs) have been described as key players in the inflammation cascade after neuronal injury; however, their role and possible inhibition in the context of acute traumatic SCIs have not been widely studied. Here, we review the relationship between SCI and IL-6 concentrations in the CSF and serum of individuals after traumatic SCIs. Furthermore, we explore the dual IL-6 signaling pathways and their relevance for future IL-6 targeted therapies in SCI.

Alterations in the spinal cord, trigeminal nerve ganglion, and infraorbital nerve through inducing compression of the dorsal horn region at the upper cervical cord in trigeminal neuralgia

BACKGROUND

Idiopathic trigeminal neuralgia (TN) cases encountered frequently in daily practice indicate significant gaps that still need to be illuminated in the etiopathogenesis. In this study, a novel TN animal model was developed by compressing the dorsal horn (DH) of the upper cervical spinal cord.

METHODS

Eighteen rabbits were equally divided into three groups, namely control (CG), sham (SG), and spinal cord compression (SCC) groups. External pressure was applied to the left side at the C3 level in the SCC group. Dorsal hemilaminectomy was performed in the SG, and the operative side was closed without compression. No procedure was implemented in the control group. Samples from the SC, TG, and ION were taken after seven days. For the histochemical staining, damage and axons with myelin were scored using Hematoxylin and Eosin and Toluidine Blue, respectively. Immunohistochemistry, nuclei, apoptotic index, astrocyte activity, microglial labeling, and CD11b were evaluated.

RESULTS

Mechanical allodynia was observed on the ipsilateral side in the SCC group. In addition, both the TG and ION were partially damaged from SC compression, which resulted in significant histopathological changes and increased the expression of all markers in both the SG and SCC groups compared to that in the CG. There was a notable increase in tissue damage, an increase in the number of apoptotic nuclei, an increase in the apoptotic index, an indication of astrocytic gliosis, and an upsurge in microglial cells. Significant increases were noted in the SG group, whereas more pronounced significant increases were observed in the SCC group. Transmission electron microscopy revealed myelin damage, mitochondrial disruption, and increased anchoring particles. Similar changes were observed to a lesser extent in the contralateral spinal cord.

CONCLUSION

Ipsilateral trigeminal neuropathic pain was developed due to upper cervical SCC. The clinical finding is supported by immunohistochemical and ultrastructural changes. Thus, alterations in the DH due to compression of the upper cervical region should be considered as a potential cause of idiopathic TN.

Investigation into effects of tocilizumab and epoetin beta in rats with experimental sciatic nerve injury model

OBJECTIVE

To investigate the effects of tocilizumab (TCZ), epoetin beta (EPO), and their combination on nerve regeneration in a sciatic nerve injury model.

MATERIALS AND METHOD

Male Sprague-Dawley rats were divided into (-) negative control, sham, TCZ, EPO ((+) positive control), and TCZ+EPO groups. The TCZ group received TCZ (8 mg/kg intraperitoneal) immediately after surgery. On day 14th, the EPO group received EPO (5000 IU/kg, intraperitoneal); the TCZ+EPO group received TCZ (8 mg/kg, intraperitoneal), EPO (5000 IU/kg, intraperitoneal), and TCZ (8 mg/kg, intraperitoneal) post-surgery. Motor and sensory functions were assessed pre and post-surgery. Lipid peroxidation and oxidative stress parameters were evaluated biochemically in the serum, and sciatic nerve tissue was evaluated histopathologically using haematoxylin-Eosin and Masson trichrome staining.

CONCLUSIONS

TCZ and EPO decreased nerve injury effects by increasing motor and sensory conduction velocities of the sciatic nerve. Biochemically, TCZ and EPO significantly increased Superoxide Dismutase, Catalase, and Glutathione peroxidase 4 levels while decreasing Lipid Peroxidation levels (p=0.001). Histopathologically, neuronal degeneration following nerve injury was decreased in the groups receiving TCZ and EPO (p=0.001). EPO and TCZ attenuate the adverse effects of nerve injury. However, the TCZ+EPO treatment favoured biochemical activities over tissue and functional activities. This has been confirmed functionally, biochemically, and histopathologically.

Immune drivers of physiological and pathological pain

Physiological pain serves as a warning of exposure to danger and prompts us to withdraw from noxious stimuli to prevent tissue damage. Pain can also alert us of an infection or organ dysfunction and aids in locating such malfunction. However, there are instances where pain is purely pathological, such as unresolved pain following an inflammation or injury to the nervous system, and this can be debilitating and persistent. We now appreciate that immune cells are integral to both physiological and pathological pain, and that pain, in consequence, is not strictly a neuronal phenomenon. Here, we discuss recent findings on how immune cells in the skin, nerve, dorsal root ganglia, and spinal cord interact with somatosensory neurons to mediate pain. We also discuss how both innate and adaptive immune cells, by releasing various ligands and mediators, contribute to the initiation, modulation, persistence, or resolution of various modalities of pain. Finally, we propose that the neuroimmune axis is an attractive target for pain treatment, but the challenges in objectively quantifying pain preclinically, variable sex differences in pain presentation, as well as adverse outcomes associated with immune system modulation, all need to be considered in the development of immunotherapies against pain.

Dissecting Genetic Mechanisms of Differential Locomotion, Depression, and Allodynia after Spinal Cord Injury in Three Mouse Strains

Strain differences have been reported for motor behaviors, and only a subset of spinal cord injury (SCI) patients develop neuropathic pain, implicating genetic or genomic contribution to this condition. Here, we evaluated neuropsychiatric behaviors in A/J, BALB/c, and C57BL/6 male mice and tested genetic or genomic alterations following SCI. A/J and BALB/c naive mice showed significantly less locomotor activity and greater anxiety-like behavior than C57BL/6 mice. Although SCI elicited locomotor dysfunction, C57BL/6 and A/J mice showed the best and the worst post-traumatic recovery, respectively. Mild (m)-SCI mice showed deficits in gait dynamics. All moderate/severe SCI mice exhibited similar degrees of anxiety/depression. mSCI in BALB/c and A/J mice resulted in depression, whereas C57BL/6 mice did not exhibit depression. mSCI mice had significantly lower mechanical thresholds than their controls, indicating high cutaneous hypersensitivity. C57BL/6, but not A/J and BLAB/c mice, showed significantly lower heat thresholds than their controls. C57BL/6 mice exhibited spontaneous pain. RNAseq showed that genes in immune responses and wound healing were upregulated, although A/J mice showed the largest increase. The cell cycle and the truncated isoform of trkB genes were robustly elevated in SCI mice. Thus, different genomics are associated with post-traumatic recovery, underscoring the likely importance of genetic factors in SCI.

Molecular pathway of pancreatic cancer-associated neuropathic pain

The pancreas is a heterocrine gland that has both exocrine and endocrine parts. Most pancreatic cancer begins in the cells that line the ducts of the pancreas and is called pancreatic ductal adenocarcinoma (PDAC). PDAC is the most encountered pancreatic cancer type. One of the most important characteristic features of PDAC is neuropathy which is primarily due to perineural invasion (PNI). PNI develops tumor microenvironment which includes overexpression of fibroblasts cells, macrophages, as well as angiogenesis which can be responsible for neuropathy pain. In tumor microenvironment inactive fibroblasts are converted into an active form that is cancer-associated fibroblasts (CAFs). Neurotrophins they also increase the level of Substance P, calcitonin gene-related peptide which is also involved in pain. Matrix metalloproteases are the zinc-associated proteases enzymes which activates proinflammatory interleukin-1β into its activated form and are responsible for release and activation of Substance P which is responsible for neuropathic pain by transmitting pain signal via dorsal root ganglion. All the molecules and their role in being responsible for neuropathic pain are described below.

NF-κB and JAK/STAT Signaling Pathways as Crucial Regulators of Neuroinflammation and Astrocyte Modulation in Spinal Cord Injury

Spinal cord injury (SCI) leads to significant functional impairments below the level of the injury, and astrocytes play a crucial role in the pathophysiology of SCI. Astrocytes undergo changes and form a glial scar after SCI, which has traditionally been viewed as a barrier to axonal regeneration and functional recovery. Astrocytes activate intracellular signaling pathways, including nuclear factor κB (NF-κB) and Janus kinase-signal transducers and activators of transcription (JAK/STAT), in response to external stimuli. NF-κB and STAT3 are transcription factors that play a pivotal role in initiating gene expression related to astrogliosis. The JAK/STAT signaling pathway is essential for managing secondary damage and facilitating recovery processes post-SCI: inflammation, glial scar formation, and astrocyte survival. NF-κB activation in astrocytes leads to the production of pro-inflammatory factors by astrocytes. NF-κB and STAT3 signaling pathways are interconnected: NF-κB activation in astrocytes leads to the release of interleukin-6 (IL-6), which interacts with the IL-6 receptor and initiates STAT3 activation. By modulating astrocyte responses, these pathways offer promising avenues for enhancing recovery outcomes, illustrating the crucial need for further investigation into their mechanisms and therapeutic applications in SCI treatment.

IL-6/JAK2/STAT3 axis mediates neuropathic pain by regulating astrocyte and microglia activation after spinal cord injury

After spinal cord injury (SCI), the control of activated glial cells such as microglia and astrocytes has emerged as a promising strategy for neuropathic pain management. However, signaling mechanism involved in glial activation in the process of neuropathic pain development and maintenance after SCI is not well elucidated. In this study, we investigated the potential role and mechanism of the JAK2/STAT3 pathway associated with glial cell activation in chronic neuropathic pain development and maintenance after SCI. One month after contusive SCI, the activation of JAK2/STAT3 pathway was markedly upregulated in both microglia and astrocyte in nociceptive processing regions of the lumbar spinal cord. In addition, both mechanical allodynia and thermal hyperalgesia was significantly inhibited by a JAK2 inhibitor, AG490. In particular, AG490 treatment inhibited both microglial and astrocyte activation in the lumbar (L) 4-5 dorsal horn and significantly decreased levels of p-p38MAPK, p-ERK and p-JNK, which are known to be activated in microglia (p-p38MAPK and p-ERK) and astrocyte (p-JNK). Experiments using primary cell cultures also revealed that the JAK2/STAT3 pathway promoted microglia and astrocyte activation after lipopolysaccharide stimulation. Furthermore, JAK2/STAT3 signaling and pain behaviors were significantly attenuated when the rats were treated with anti-IL-6 antibody. Finally, minocycline, a tetracycline antibiotic, inhibited IL-6/JAK2/STAT3 signaling pathway in activated glial cells and restored nociceptive thresholds and the hyperresponsiveness of dorsal neurons. These results suggest an important role of the IL-6/JAK2/STAT3 pathway in the activation of microglia and astrocytes and in the maintenance of chronic below-level pain after SCI.

Neuroinflammation: Breaking barriers and bridging gaps

Neurons are the cells of the nervous system and are responsible for every thought, movement and perception. Immune cells are the cells of the immune system, constantly protecting from foreign pathogens. Understanding the interaction between the two systems is especially important in disease states such as autoimmune or neurodegenerative disease. Unfortunately, this interaction is typically detrimental to the host. However, recent efforts have focused on how neurons and immune cells interact, either directly or indirectly, following traumatic injury to the nervous system. The outcome of this interaction can be beneficial - leading to successful neural repair, or detrimental - leading to functional deficits, depending on where the injury occurs. This review will discuss our understanding of neuron-immune cell interactions after traumatic injury to both the peripheral and central nervous system.

Inhibiting IL-6 in medicine: a new twist to sustain inhibition of his cytokine tin the therapy of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a chronic, progressive disease characterized by an increase in blood pressure in the lungs' arteries. It can occur in a variety of species, including humans, dogs, cats, and horses. To date, PAH has a high mortality rate in both veterinary and human medicine, often due to complications such as heart failure. The complex pathological mechanisms of PAH involve multiple cellular signalling pathways at various levels. IL-6 is a powerful pleiotropic cytokine that regulates several phases of immune response, inflammation, and tissue remodelling. The hypothesis of this study was that the use of an IL-6 antagonist in PAH could interrupt or mitigate the cascade of events that leads to the progression of the disease and the worsening of clinical outcome, as well as tissue remodelling. In this study, we used two pharmacological protocols with an IL-6 receptor antagonist in a monocrotaline-induced PAH model in rats. Our results showed that the use of an IL-6 receptor antagonist had a significant protective effect, ameliorating both haemodynamic parameters, lung and cardiac function, tissue remodelling, and the inflammation associated with PAH. The results of this study suggest that the inhibition IL-6 could be a useful pharmacological strategy in PAH, in both human and veterinary medicine.

Analysis of the Influence of IL-6 and the Activation of the Jak/Stat3 Pathway in Fibromyalgia

Background: Fibromyalgia is a medical condition that affects a small percentage of the population, with no known effective treatment. There is evidence to suggest that inflammation is a key factor in the nerve sensitization that characterizes the disorder. Therefore, this paper concentrates on the role of IL-6 in fibromyalgia and the related pain-like symptoms. Methods: This work aimed to evaluate Sprague–Dawley rats, which were injected for three consecutive days with 1 mg/kg of reserpine; IL-6-R Ab was intraperitoneally injected at 1.5 mg/kg seven days after the first reserpine injection. Behavioral analyses were conducted at the beginning of the experiment and at seven and twenty-one days from the first reserpine injection. At this timepoint, the animals were sacrificed, and tissues were collected for molecular and histological analysis. Results: Our data showed the analgesic effect of IL-6-R-Ab administration on mechanical allodynia and thermal hyperalgesia. Additionally, the reserpine + IL-6-R-Ab group showed a reduced expression of the pain-related mediators cFOS and NFG and reduced levels of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) and chemokines (Cxcl5, Cxcl10 and Cx3cl1). From the molecular point of view, the IL-6-R-Ab administration reduced the gp130 phosphorylation and the activation of the Jak/STAT3 pathway. Additionally, the IL-6-R Ab reduced the activation of neuroinflammatory cells. Conclusions: Our study showed that IL-6 plays a crucial role in fibromyalgia by triggering the Jak/STAT3 pathway, leading to an increase in chemokine levels and activating glial cells.

Tocilizumab promotes repair of spinal cord injury by facilitating the restoration of tight junctions between vascular endothelial cells

BACKGROUND

Our previous study demonstrated that M1 macrophages could impair tight junctions (TJs) between vascular endothelial cells by secreting interleukin-6 (IL-6) after spinal cord injury (SCI). Tocilizumab, as a humanized IL-6 receptor (IL-6R) monoclonal antibody approved for the clinic, has been applied in the treatment of neurological diseases in recent years, but the treatment effect of Tocilizumab on the TJs restoration of the blood-spinal cord barrier (BSCB) after SCI remains unclear. This study aimed to explore the effect of Tocilizumab on the restoration of TJs between vascular endothelial cells and axon regeneration after SCI.

METHODS

In this study, the mouse complete spinal cord crush injury model was used, and Tocilizumab was continuously injected intrathecally until the day of sample collection. A PBS injection in the same location was included as a control. At 14 days postinjury (dpi) and 28 dpi, spinal cord tissue sections were examined via tissue immunofluorescence. The Basso Mouse Scale (BMS) scores and footprint analysis were used to verify the effect of Tocilizumab on the recovery of motor function in mice after SCI.

RESULTS

We demonstrated that depletion of macrophages has no effect on axon regeneration and motor functional recovery after SCI, but mice subjected to Tocilizumab showed a significant increase in axon regeneration and a better recovery in motor function during the chronic phase after SCI. Moreover, our study demonstrated that at 14 and 28 dpi, the expression of claudin-5 (CLDN5) and zonula occludens-1 (ZO-1) between vascular endothelial cells was significantly increased and the leakage of BSCB was significantly reduced in the injured core after daily intrathecal injection of Tocilizumab. Notably, the infiltration of CD68⁺ macrophages/microglia and the formation of fibrotic scar were decreased in the injured core after Tocilizumab treatment. Tocilizumab treatment could effectively reduce the IL-6 expression in macrophages in the injured core.

CONCLUSION

The application of Tocilizumab to antagonize IL-6R can effectively reduce the expression of IL-6 in macrophages and facilitate TJs restoration of the BSCB, which is beneficial for axon regeneration and motor functional recovery after SCI. Hence, Tocilizumab treatment is a potential therapeutic strategy for SCI.

Resveratrol suppresses neuroinflammation to alleviate mechanical allodynia by inhibiting Janus kinase 2/signal transducer and activator of transcription 3 signaling pathway in a rat model of spinal cord injury

Background

Neuropathic pain (NP) is one of intractable complications of spinal cord injury (SCI) and lacks effective treatment. Resveratrol (Res) has been shown to possess potent anti-inflammatory and anti-nociceptive effects. In this study, we investigated the analgesic effect of Res and its underlying mechanism in a rat model of SCI.

Methods

The rat thoracic (T10) spinal cord contusion injury model was established, and mechanical thresholds were evaluated during an observation period of 21 days. Intrathecal administration with Res (300 μg/10 μl) was performed once a day for 7 days after the operation. On postoperative day 7, the expressions of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) were determined by enzyme-linked immunosorbent assay (ELISA) and Real-time quantitative PCR (RT-qPCR), the expression of Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway was determined by western blot and RT-qPCR, and the co-labeled phospho-STAT3 (p-STAT3) with neuronal nuclear antigen (NeuN), glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba-1) were explored by double immunofluorescence staining in the lumbar spinal dorsal horns. The temporal changes of p-STAT3 were investigated by western blot on the 1st, 3rd, 7th, 14th, and 21st days after the operation.

Results

Intrathecal administration with Res for 7 successive days alleviated mechanical allodynia of rats during the observation period. Meanwhile, treatment with Res suppressed the production of pro-inflammatory factors TNF-α, IL-1β and IL-6, and inhibited the expressions of phospho-JAK2 and p-STAT3 in the lumbar spinal dorsal horns on postoperative day 7. Additionally, the protein expression of p-STAT3 was significantly increased on the 1st day following the operation and remained elevated during the next 21 days, immunofluorescence suggested that the up-regulated p-STAT3 was co-located with glial cells and neurons.

Conclusion

Our current results indicated that intrathecal administration with Res effectively alleviated mechanical allodynia after SCI in rats, and its analgesic mechanism might be to suppress neuroinflammation by partly inhibiting JAK2/STAT3 signaling pathway.

Anti-interleukin-6 receptor antibody improves allodynia and cognitive impairment in mice with neuropathic pain following partial sciatic nerve ligation

Neuropathic pain caused by nerve injury presents with severe spontaneous pain and a range of comorbidities, including deficits in higher executive functioning, none of which are adequately treated with current analgesics. Interleukin-6 (IL-6), a proinflammatory cytokine, is critically involved in the development and maintenance of central sensitization. However, the roles of IL-6 in neuropathic pain and related comorbidities have yet to be fully clarified. The present study examined the effect of MR16-1, an anti-IL-6 receptor antibody and inhibits IL-6 activity, on allodynia and cognitive impairment in mice with neuropathic pain following partial sciatic nerve ligation (PSNL). Significant upregulation of IL-6 expression was observed in the hippocampus in PSNL mice. Intranasal administration of MR16-1 significantly improved cognitive impairment but not allodynia in PSNL mice. Intranasal MR16-1 blocked PSNL-induced degenerative effects on hippocampal neurons. Intraperitoneal administration of MR16-1 suppressed allodynia but not cognitive impairment of PSNL mice. The findings suggest that cognitive impairment associated with neuropathic pain is mediated through changes in hippocampus induced by IL-6. These data also suggest that IL-6 mediated peripheral inflammation underlies allodynia, and IL-6 mediated inflammation in the central nervous system underlies cognitive impairment associated with neuropathic pain, and further suggest the therapeutic potential of blocking IL-6 functioning by blocking its receptor.

The Role of Neuro-Immune Interactions in Chronic Pain: Implications for Clinical Practice

Chronic pain remains a public health problem and contributes to the ongoing opioid epidemic. Current pain management therapies still leave many patients with poorly controlled pain, thus new or improved treatments are desperately needed. One major challenge in pain research is the translation of preclinical findings into effective clinical practice. The local neuroimmune interface plays an important role in the initiation and maintenance of chronic pain and is therefore a promising target for novel therapeutic development. Neurons interface with immune and immunocompetent cells in many distinct microenvironments along the nociceptive circuitry. The local neuroimmune interface can modulate the activity and property of the neurons to affect peripheral and central sensitization. In this review, we highlight a specific subset of many neuroimmune interfaces. In the central nervous system, we examine the interface between neurons and microglia, astrocytes, and T lymphocytes. In the periphery, we profile the interface between neurons in the dorsal root ganglion with T lymphocytes, satellite glial cells, and macrophages. To bridge the gap between preclinical research and clinical practice, we review the preclinical studies of each neuroimmune interface, discuss current clinical treatments in pain medicine that may exert its action at the neuroimmune interface, and highlight opportunities for future clinical research efforts.

Minocycline prevents chronic restraint stress-induced vulnerability to developing cocaine self-administration and associated glutamatergic mechanisms: a potential role of microglia

Stressful experience-induced cocaine-related behaviors are associated with a significant impairment of glutamatergic mechanisms in the Nucleus Accumbens core (NAcore). The hallmarks of disrupted glutamate homeostasis following restraint stress are the enduring imbalance of glutamate efflux after a cocaine stimulus and increased basal concentrations of extracellular glutamate attributed to GLT-1 downregulation in the NAcore. Glutamate transmission is tightly linked to microglia functioning. However, the role of microglia in the biological basis of stress-induced addictive behaviors is still unknown. By using minocycline, a potent inhibitor of microglia activation with anti-inflammatory properties, we determined whether microglia could aid chronic restraint stress (CRS)-induced glutamate homeostasis disruption in the NAcore, underpinning stress-induced cocaine self-administration. In this study, adult male rats were restrained for 2 h/day for seven days (day 1-7). From day 16 until completing the experimental protocol, animals received a vehicle or minocycline treatment (30 mg/Kg/12h i.p.). On day 21, animals were assigned to microscopic, biochemical, neurochemical or behavioral studies. We confirm that the CRS-induced facilitation of cocaine self-administration is associated with enduring GLT-1 downregulation, an increase of basal extracellular glutamate and postsynaptic structural plasticity in the NAcore. These alterations were strongly related to the CRS-induced reactive microglia and increased TNF-α mRNA and protein expression, since by administering minocycline, the impaired glutamate homeostasis and the facilitation of cocaine self-administration were prevented. Our findings are the first to demonstrate that minocycline suppresses the CRS-induced facilitation of cocaine self-administration and glutamate homeostasis disruption in the NAcore. A role of microglia is proposed for the development of glutamatergic mechanisms underpinning stress-induced vulnerability to cocaine addiction.

Pain Symptoms in Optic Neuritis

Signs and symptoms of optic neuritis (ON), an autoimmune disorder of the central nervous system (CNS), differ between patients. Pain, which is commonly reported by ON patients, may be the major reason for some patients to visit the clinic. This article reviews the presence of pain related to ON with respect to underlying disorders, including multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), and myelin oligodendrocyte glycoprotein associated disease (MOGAD). The aim of this review is to provide an overview of pain symptoms in accordance with the context of various pathophysiological explanations, assist in differential diagnosis of ON patients, especially at the onset of disease, and make recommendations to aid physicians make decisions for follow up diagnostic examinations.

Optical Coherence Tomography Reveals Longitudinal Changes in Retinal Damage Under Different Treatments for Neuromyelitis Optica Spectrum Disorder

Background: Progressive retinal neuroaxonal damage after acute optic neuritis may occur in neuromyelitis optica spectrum disorder (NMOSD). However, it is unclear if treatments used to prevent attacks influence neurodegeneration.

Objectives: We aimed to investigate retinal damage in patients treated with disease-modifying drugs in a longitudinal study.

Methods: We retrospectively included 50 patients with aquaporin 4-antibody-seropositive NMOSD. Peripapillary retinal nerve fiber layer (pRNFL) thickness, macular ganglion cell complex (mGCC) thickness, total macular volume (TMV), and optic disc measures were acquired by spectral domain optical coherence tomography in patients treated with tocilizumab, rituximab, and azathioprine.

Results: Longitudinally, in eyes with a history of ON (NMOSD^ON+), we observed annual thinning of mGCC [tocilizumab: −1.77 (−3.44, −0.09) μm, p = 0.041; rituximab: −2.03 (−3.58, −0.48) μm, p = 0.017; azathioprine: −1.79 (−2.22, −1.37) μm, p < 0.001], and pRNFL [tocilizumab: −2.07 (−0.75, −3.39) μm, p = 0.005; rituximab: −2.18 (−0.36, −4.00) μm, p = 0.023; azathioprine: −2.37 (−0.98, −3.75) μm, p = 0.003], reduced TMV [tocilizumab: −0.12 (−0.22, −0.01) mm³, p = 0.028; rituximab: −0.15 (−0.21, −0.08) mm³, p = 0.001; azathioprine: −0.12 (−0.20, −0.04) mm³, p = 0.006], and increased cup area [tocilizumab: 0.08 (−0.01, 0.16) mm², p = 0.010; rituximab: 0.07 (0.01, 0.12) mm², p = 0.019; azathioprine: 0.14 (0.02, 0.26) mm², p = 0.023]. However, we detected no significant differences in annual changes in mGCC, pRNFL, TMV, and cup area between patients with tocilizumab, rituximab, and azathioprine in NMOSD^ON+ eyes. NMOSD^ON− eyes did not display mGCC or pRNFL thinning in patients treated with tocilizumab and rituximab. Intriguingly, we observed significant thinning of mGCC in patients treated with azathioprine compared with tocilizumab [−0.84 (−1.50, −0.18) μm vs. −0.19 (−0.87, 0.48) μm, p = 0.012] and rituximab [−0.84 (−1.50, −0.18) μm vs. −0.07 (−1.25, −2.51) μm, p = 0.015] in NMOSD^ON− eyes.

Conclusions: This study demonstrated that retinal ganglion cell loss is independent of ON attacks in NMOSD. Tocilizumab and rituximab may delay mGCC thinning in NMOSD^ON− eyes compared with azathioprine.

Role of IL-6 in the regulation of neuronal development, survival and function

The pleiotropic cytokine interleukin-6 (IL-6) is emerging as a molecule with both beneficial and destructive potentials. It can exert opposing actions triggering either neuron survival after injury or causing neurodegeneration and cell death in neurodegenerative or neuropathic disorders. Importantly, neurons respond differently to IL-6 and this critically depends on their environment and whether they are located in the peripheral or the central nervous system. In addition to its hub regulator role in inflammation, IL-6 is recently emerging as an important regulator of neuron function in health and disease, offering exciting possibilities for more mechanistic insight into the pathogenesis of mental, neurodegenerative and pain disorders and for developing novel therapies for diseases with neuroimmune and neurogenic pathogenic components.

Aromatherapy Plus Music Therapy Improve Pain Intensity and Anxiety Scores in Patients With Breast Cancer During Perioperative Periods: A Randomized Controlled Trial

INTRODUCTION

To investigate the effect of perioperative aromatherapy (AT) or/plus music therapy (MT) on pain and anxiety level, and the potential mechanism in women experiencing breast cancer surgery.

METHODS

A total of 160 patients with breast cancer were randomly assigned in a 1:1:1:1 ratio to receive usual care (UC), AT, MT, or combination therapy (CT) during perioperative periods. Pain intensity and anxiety scores were measured by visual analog scale. Interleukin (IL)-6 and high mobility group box 1 (HMGB-1) were measured by enzyme-linked immunosorbent assay.

RESULTS

There was a significant group effect on pain, anxiety, and IL-6 and HMGB-1 levels, with the greatest improvement occurring in the CT group (P < .001). Compared with the UC group, the AT and MT groups had lower mean changes of pain intensity and IL-6 and HMGB-1 levels, and greater anxiety reduction (P < .001). However, the differences between the AT and MT groups did not reach significance (P > .05).

CONCLUSION

In patients with breast cancer, perioperative CT achieves greater pain improvement and anxiety reduction and less marked increase in IL-6 and HMGB-1 levels. These results suggest that CT is an acceptable complementary and alternative medicine for breast cancer patients.

Emerging Role of Serum Glucocorticoid-Regulated Kinase 1 in Pathological Pain

Currently, the management of acute and chronic pain in clinical practice remains unsatisfactory due to the existence of limited effective treatments, and novel therapeutic strategies for pathological pain are urgently needed. In the past few decades, the role of serum and glucocorticoid-inducible kinase 1 (SGK1) in the development of pain and diurnal rhythms has been implicated in numerous studies. The expression levels of SGK1 mRNA and protein were found to be elevated in the spinal cord and brain in various pathological pain models. Blocking SGK1 significantly attenuated pain-like responses and the development of pathological pain. These studies provide strong evidence that SGK1 plays a role in the development of various types of pathological pain and that targeting SGK1 may be a novel therapeutic strategy for pain management. In this review article, we provide evidence from animal models for the potential role of SGK1 in the regulation of pathological pain caused by inflammation, nerve injury, psychiatric disorders, and chronic opioid exposure.

On the therapeutic targets and pharmacological treatments for pain relief following spinal cord injury: A mechanistic review

Spinal cord injury (SCI) is globally considered as one of the most debilitating disorders, which interferes with daily activities and life of the affected patients. Despite many developments in related recognizing and treating procedures, post-SCI neuropathic pain (NP) is still a clinical challenge for clinicians with no distinct treatments. Accordingly, a comprehensive search was conducted in PubMed, Medline, Scopus, Web of Science, and national database (SID and Irandoc). The relevant articles regarding signaling pathways, therapeutic targets and pharmacotherapy of post-SCI pain were also reviewed. Data were collected with no time limitation until November 2020. The present study provides the findings on molecular mechanisms and therapeutic targets, as well as developing the critical signaling pathways to introduce novel neuroprotective treatments of post-SCI pain. From the pathophysiological mechanistic point of view, post-SCI inflammation activates the innate immune system, in which the immune cells elicit secondary injuries. So, targeting the critical signaling pathways for pain management in the SCI population has significant importance in providing new treatments. Indeed, several receptors, ion channels, excitatory neurotransmitters, enzymes, and key signaling pathways could be used as therapeutic targets, with a pivotal role of n-methyl-D-aspartate, gamma-aminobutyric acid, and inflammatory mediators. The current review focuses on conventional therapies, as well as crucial signaling pathways and promising therapeutic targets for post-SCI pain to provide new insights into the clinical treatment of post-SCI pain. The need to develop innovative delivery systems to treat SCI is also considered.

Intravenous transplantation of olfactory ensheathing cells reduces neuroinflammation after spinal cord injury via interleukin-1 receptor antagonist

Rationale: Olfactory ensheathing cell (OEC) transplantation has emerged as a promising therapy for spinal cord injury (SCI) repair. In the present study, we explored the possible mechanisms of OECs transplantation underlying neuroinflammation modulation.

Methods: Spinal cord inflammation after intravenous OEC transplantation was detected in vivo and ex vivo by translocator protein PET tracer [¹⁸F]F-DPA. To track transplanted cells, OECs were transduced with enhanced green fluorescent protein (eGFP) and HSV1-39tk using lentiviral vector and were monitored by fluorescence imaging and [¹⁸F]FHBG study. Protein microarray analysis and ELISA studies were employed to analyze differential proteins in the injured spinal cord after OEC transplantation. The anti-inflammation function of the upregulated protein was also proved by in vitro gene knocking down experiments and OECs/microglia co-culture experiment.

Results: The inflammation in the spinal cord was decreased after OEC intravenous transplantation. The HSV1-39tk-eGFP-transduced OECs showed no accumulation in major organs and were found at the injury site. After OEC transplantation, in the spinal cord tissues, the interleukin-1 receptor antagonist (IL-1Ra) was highly upregulated while many chemokines, including pro-inflammatory chemokines IL-1α, IL-1β were downregulated. In vitro studies confirmed that lipopolysaccharide (LPS) stimulus triggered OECs to secrete IL-1Ra. OECs significantly suppressed LPS-stimulated microglial activity, whereas IL-1Ra gene knockdown significantly reduced their ability to modulate microglial activity.

Conclusion: The OECs that reached the lesion site were activated by the release of pro-inflammatory cytokines from activated microglia in the lesion site and secreted IL-1Ra to reduce neuroinflammation. Intravenous transplantation of OECs has high therapeutic effectiveness for the treatment of SCI via the secretion of IL-1Ra to reduce neuroinflammation.

The gut-brain axis and beyond: Microbiome control of spinal cord injury pain in humans and rodents

Spinal cord injury (SCI) is a devastating injury to the central nervous system in which 60 to 80% of patients experience chronic pain. Unfortunately, this pain is notoriously difficult to treat, with few effective options currently available. Patients are also commonly faced with various compounding injuries and medical challenges, often requiring frequent hospitalization and antibiotic treatment. Change in the gut microbiome from the "normal" state to one of imbalance, referred to as gut dysbiosis, has been found in both patients and rodent models following SCI. Similarities exist in the bacterial changes observed after SCI and other diseases with chronic pain as an outcome. These changes cause a shift in the regulation of inflammation, causing immune cell activation and secretion of inflammatory mediators that likely contribute to the generation/maintenance of SCI pain. Therefore, correcting gut dysbiosis may be used as a tool towards providing patients with effective pain management and improved quality of life.

Tocilizumab, a Potent Interleukin-6 Receptor Inhibitor, Decreases Bone Resorption and Increases the Rate of Bacterial Infection After Tooth Extraction in Rats

PURPOSE

Our objective was to evaluate the influence of pretreatment with tocilizumab (TCZ) in bone healing after tooth extraction in rats.

METHODS

Wistar male rats were equally divided into sham (ie, nonoperated), saline (both treated with 0.1 ml/kg saline), and six TCZ groups treated with 1, 2, 4, 8, 16, and 32 mg/kg TCZ (TCZ1 to TCZ32, respectively). Twenty-four hours after administration of vehicle or TCZ, exodontia of the first lower left molar was performed, and the animals were euthanized three days later for hematological analysis and organ (liver, spleen, and kidney mass indexes, and histological evaluation), gingiva (myeloperoxidase [MPO] assay), and mandible (radiographic, histomorphometric analysis, and IL-6 immunostaining) evaluation. Analysis of variance/Bonferroni test (statistical significance, P < .05) was performed using GraphPad Prism version 5.0 (GraphPad Inc, San Diego, CA, USA).

RESULTS

There was no difference in radiographic results; however, leukopenia (P = .039) and neutropenia (P < .001) were statistically significant in the TCZ16 and TCZ32 groups. Weight loss (P < .001) and reduced liver index (P = .001) were significantly dose-dependent; however, no histological alterations were observed in the other organs. Osteoclast counts were reduced in groups TCZ4 to TCZ32 (P < .001), and IL-6 immunostaining increased in the TCZ8 to TCZ32 groups (P < .001). Alveolar infection rates increased in groups TCZ4 to TCZ32 (P < .001), and MPO had a biphasic response, exhibiting a reduction in groups TCZ2 and TCZ4, and an increase in group TCZ32 (P = .004).

CONCLUSION

TCZ-induced immunosuppression led to a reduction in osteoclast function, an increase in alveolar infection, and compensatory neutrophil infiltration.

Regional Hyperexcitability and Chronic Neuropathic Pain Following Spinal Cord Injury

Spinal cord injury (SCI) causes maladaptive changes to nociceptive synaptic circuits within the injured spinal cord. Changes also occur at remote regions including the brain stem, limbic system, cortex, and dorsal root ganglia. These maladaptive nociceptive synaptic circuits frequently cause neuronal hyperexcitability in the entire nervous system and enhance nociceptive transmission, resulting in chronic central neuropathic pain following SCI. The underlying mechanism of chronic neuropathic pain depends on the neuroanatomical structures and electrochemical communication between pre- and postsynaptic neuronal membranes, and propagation of synaptic transmission in the ascending pain pathways. In the nervous system, neurons are the only cell type that transmits nociceptive signals from peripheral receptors to supraspinal systems due to their neuroanatomical and electrophysiological properties. However, the entire range of nociceptive signaling is not mediated by any single neuron. Current literature describes regional studies of electrophysiological or neurochemical mechanisms for enhanced nociceptive transmission post-SCI, but few studies report the electrophysiological, neurochemical, and neuroanatomical changes across the entire nervous system following a regional SCI. We, along with others, have continuously described the enhanced nociceptive transmission in the spinal dorsal horn, brain stem, thalamus, and cortex in SCI-induced chronic central neuropathic pain condition, respectively. Thus, this review summarizes the current understanding of SCI-induced neuronal hyperexcitability and maladaptive nociceptive transmission in the entire nervous system that contributes to chronic central neuropathic pain.

Transcriptional Profiling of Non-injured Nociceptors After Spinal Cord Injury Reveals Diverse Molecular Changes

Traumatic spinal cord injury (SCI) has devastating implications for patients, including a high predisposition for developing chronic pain distal to the site of injury. Chronic pain develops weeks to months after injury, consequently, patients are treated after irreparable changes have occurred. Nociceptors are central to chronic pain; however, the diversity of this cellular population presents challenges to understanding mechanisms and attributing pain modalities to specific cell types. To begin to address how peripheral sensory neurons below the injury level may contribute to the below-level pain reported by SCI patients, we examined SCI-induced changes in gene expression in lumbar dorsal root ganglia (DRG) below the site of injury. SCI was performed at the T10 vertebral level, with injury produced by a vessel clip with a closing pressure of 15 g for 1 min. Alterations in gene expression produce long-term sensory changes, therefore, we were interested in studying SCI-induced transcripts before the onset of chronic pain, which may trigger changes in downstream signaling pathways and ultimately facilitate the transmission of pain. To examine changes in the nociceptor subpopulation in DRG distal to the site of injury, we retrograde labeled sensory neurons projecting to the hairy hindpaw skin with fluorescent dye and collected the corresponding lumbar (L2–L6) DRG 4 days post-injury. Following dissociation, labeled neurons were purified by fluorescence-activated cell sorting (FACS). RNA was extracted from sorted sensory neurons of naïve, sham, or SCI mice and sequenced. Transcript abundances validated that the desired population of nociceptors were isolated. Cross-comparisons to data sets from similar studies confirmed, we were able to isolate our cells of interest and identify a unique pattern of gene expression within a subpopulation of neurons projecting to the hairy hindpaw skin. Differential gene expression analysis showed high expression levels and significant transcript changes 4 days post-injury in SCI cell populations relevant to the onset of chronic pain. Regulatory interrelationships predicted by pathway analysis implicated changes within the synaptogenesis signaling pathway as well as networks related to inflammatory signaling mechanisms, suggesting a role for synaptic plasticity and a correlation with pro-inflammatory signaling in the transition from acute to chronic pain.

Crotoxin Conjugated to SBA-15 Nanostructured Mesoporous Silica Induces Long-Last Analgesic Effect in the Neuropathic Pain Model in Mice

Neuropathic pain is a disease caused by structural and functional plasticity in central and peripheral sensory pathways that produce alterations in nociceptive processing. Currently, pharmacological treatment for this condition remains a challenge. Crotoxin (CTX), the main neurotoxin of Crotalus durissus terrificus rattlesnake venom, has well described prolonged anti-inflammatory and antinociceptive activities. In spite of its potential benefits, the toxicity of CTX remains a limiting factor for its use. SBA-15 is an inert nanostructured mesoporous silica that, when used as a vehicle, may reduce toxicity and potentiate the activity of different compounds. Based on this, we propose to conjugate crotoxin with SBA-15 (CTX:SBA-15) in order to investigate if when adsorbed to silica, CTX would have its toxicity reduced and its analgesic effect enhanced in neuropathic pain induced by the partial sciatic nerve ligation (PSNL) model. SBA-15 enabled an increase of 35% of CTX dosage. Treatment with CTX:SBA-15 induced a long-lasting reduction of mechanical hypernociception, without modifying the previously known pathways involved in antinociception. Moreover, CTX:SBA-15 reduced IL-6 and increased IL-10 levels in the spinal cord. Surprisingly, the antinociceptive effect of CTX:SBA-15 was also observed after oral administration. These data indicate the potential use of the CTX:SBA-15 complex for neuropathic pain control and corroborates the protective potential of SBA-15.

Mechanisms of Below-Level Pain Following Spinal Cord Injury (SCI)

Mechanisms of below-level pain are discoverable as neural adaptations rostral to spinal injury. Accordingly, the strategy of investigations summarized here has been to characterize behavioral and neural responses to below-level stimulation over time following selective lesions of spinal gray and/or white matter. Assessments of human pain and the pain sensitivity of humans and laboratory animals following spinal injury have revealed common disruptions of pain processing. Interruption of the spinothalamic pathway partially deafferents nocireceptive cerebral neurons, rendering them spontaneously active and hypersensitive to remaining inputs. The spontaneous activity among these neurons is disorganized and unlikely to generate pain. However, activation of these neurons by their remaining inputs can result in pain. Also, injury to spinal gray matter results in a cascade of secondary events, including excitotoxicity, with rostral propagation of excitatory influences that contribute to chronic pain. Establishment and maintenance of below-level pain results from combined influences of injured and spared axons in the spinal white matter and injured neurons in spinal gray matter on processing of nociception by hyperexcitable cerebral neurons that are partially deafferented. A model of spinal stenosis suggests that ischemic injury to the core spinal region can generate below-level pain. Additional questions are raised about demyelination, epileptic discharge, autonomic activation, prolonged activity of C nocireceptive neurons, and thalamocortical plasticity in the generation of below-level pain. PERSPECTIVE: An understanding of mechanisms can direct therapeutic approaches to prevent development of below-level pain or arrest it following spinal cord injury. Among the possibilities covered here are surgical and other means of attenuating gray matter excitotoxicity and ascending propagation of excitatory influences from spinal lesions to thalamocortical systems involved in pain encoding and arousal.

Pathological Mechanisms and Therapeutic Targets for Trigeminal Neuropathic Pain

Trigeminal neuropathic pain is a chronic pain condition caused by damage or inflammation of the trigeminal nerve or its branches, with both peripheral and central nervous system dysfunction contributing to the disorder. Trigeminal pain conditions present with diagnostic and therapeutic challenges to healthcare providers and often require multiple therapeutic approaches for pain reduction. This review will provide the overview of pathophysiology in peripheral and central nociceptive circuits that are involved in neuropathic pain conditions involving the trigeminal nerve and the current therapeutics that are used to treat these disorders. Recent advances in treatment of trigeminal pain, including novel therapeutics that target ion channels and receptors, gene therapy and monoclonal antibodies that have shown great promise in preclinical studies and clinical trials will also be described.

Neuregulin-1/ErbB network: An emerging modulator of nervous system injury and repair

Neuregulin-1 (Nrg-1) is a member of the Neuregulin family of growth factors with essential roles in the developing and adult nervous system. Six different types of Nrg-1 (Nrg-1 type I-VI) and over 30 isoforms have been discovered; however, their specific roles are not fully determined. Nrg-1 signals through a complex network of protein-tyrosine kinase receptors, ErbB2, ErbB3, ErbB4 and multiple intracellular pathways. Genetic and pharmacological studies of Nrg-1 and ErbB receptors have identified a critical role for Nrg-1/ErbB network in neurodevelopment including neuronal migration, neural differentiation, myelination as well as formation of synapses and neuromuscular junctions. Nrg-1 signaling is best known for its characterized role in development and repair of the peripheral nervous system (PNS) due to its essential role in Schwann cell development, survival and myelination. However, our knowledge of the impact of Nrg-1/ErbB on the central nervous system (CNS) has emerged in recent years. Ongoing efforts have uncovered a multi-faceted role for Nrg-1 in regulating CNS injury and repair processes. In this review, we provide a timely overview of the most recent updates on Nrg-1 signaling and its role in nervous system injury and diseases. We will specifically highlight the emerging role of Nrg-1 in modulating the glial and immune responses and its capacity to foster neuroprotection and remyelination in CNS injury. Nrg-1/ErbB network is a key regulatory pathway in the developing nervous system; therefore, unraveling its role in neuropathology and repair can aid in development of new therapeutic approaches for nervous system injuries and associated disorders.

Transcriptome profiling of dorsal root ganglia in a rat model of complex regional pain syndrome type-I reveals potential mechanisms involved in pain

Purpose: Complex regional pain syndrome type-I (CRPS-I) is a progressive and devastating pain condition, which remains clinically challenging. The mechanisms of CRPS-I still remain largely unknown. We aim to identify transcriptome profiles of genes relevant to pain mechanisms and major pathways involved in CRPS-I.

Methods: A rat model of chronic post-ischemia pain (CPIP) was established to mimic CRPS-I. RNA-sequencing (RNA-Seq) was used to profile transcriptome of L4-6 dorsal root ganglia (DRGs) of a rat model of CRPS-I.

Results: CPIP model rats developed persistent mechanical/thermal hyperalgesia in ipsilateral hind paw. RNA-Seq identified a total of 295 differentially expressed genes (DEGs), including 195 up- and 100 downregulated, in ipsilateral DRGs of CPIP rats compared with sham rats. The expression of several representative genes was confirmed by qPCR. Functional analysis of DEGs revealed that the most significant enriched biological processes of upregulated genes include response to lipopolysaccharide, inflammatory response and cytokine activity, which are all important mechanisms mediating pain. We further screened DEGs implicated in pain progress, genes enriched in small- to medium-sized sensory neurons and enriched in TRPV1-lineage nociceptors. By comparing our dataset with other published datasets of neuropathic or inflammatory pain models, we identified a core set of genes and pathways that extensively participate in CPIP and other neuropathic pain states.

Conclusion: Our study identified transcriptome gene changes in DRGs of an animal model of CRPS-I and could provide insights into identifying promising genes or pathways that can be potentially targeted to ameliorate CRPS-I.

Repeated Sigma-1 Receptor Antagonist MR309 Administration Modulates Central Neuropathic Pain Development After Spinal Cord Injury in Mice

Up to two-thirds of patients affected by spinal cord injury (SCI) develop central neuropathic pain (CNP), which has a high impact on their quality of life. Most of the patients are largely refractory to current treatments, and new pharmacological strategies are needed. Recently, it has been shown that the acute administration of the σ1R antagonist MR309 (previously developed as E-52862) at 28 days after spinal cord contusion results in a dose-dependent suppression of both mechanical allodynia and thermal hyperalgesia in wild-type CD-1 Swiss female mice. The present work was addressed to determine whether MR309 might exert preventive effects on CNP development by repeated administration during the first week after SCI in mice. To this end, the MR309 (16 or 32 mg/kg i.p.) modulation on both thermal hyperalgesia and mechanical allodynia development were evaluated weekly up to 28 days post-injury. In addition, changes in pro-inflammatory cytokine (TNF-α, IL-1β) expression and both the expression and activation (phosphorylation) of the N-methyl-D-aspartate receptor subunit 2B (NR2B-NMDA) and extracellular signal-regulated kinases (ERK1/2) were analyzed. The repeated treatment of SCI-mice with MR309 resulted in significant pain behavior attenuation beyond the end of the administration period, accompanied by reduced expression of central sensitization-related mechanistic correlates, including extracellular mediators (TNF-α and IL-1β), membrane receptors/channels (NR2B-NMDA) and intracellular signaling cascades (ERK/pERK). These findings suggest that repeated MR309 treatment after SCI may be a suitable pharmacologic strategy to modulate SCI-induced CNP development.

Mesenchymal stem cells and the neuronal microenvironment in the area of spinal cord injury

Cell-based technologies are used as a therapeutic strategy in spinal cord injury (SCI). Mesenchymal stem cells (MSCs), which secrete various neurotrophic factors and cytokines, have immunomodulatory, anti-apoptotic and anti-inflammatory effects, modulate reactivity/phenotype of astrocytes and the microglia, thereby promoting neuroregeneration seem to be the most promising. The therapeutic effect of MSCs is due to a paracrine mechanism of their action, therefore the survival of MSCs and their secretory phenotype is of particular importance. Nevertheless, these data are not always reported in efficacy studies of MSC therapy in SCI. Here, we provide a review with summaries of preclinical trials data evaluating the efficacy of MSCs in animal models of SCI. Based on the data collected, we have tried (1) to establish the behavior of MSCs after transplantation in SCI with an evaluation of cell survival, migration potential, distribution in the area of injured and intact tissue and possible differentiation; (2) to determine the effects MSCs on neuronal microenvironment and correlate them with the efficacy of functional recovery in SCI; (3) to ascertain the conditions under which MSCs demonstrate their best survival and greatest efficacy.

A toll-like receptor 9 antagonist restores below-level glial glutamate transporter expression in the dorsal horn following spinal cord injury

Spinal cord (SC) trauma elicits pathological changes at the primary lesion and in regions distant from the injury epicenter. Therapeutic agents that target mechanisms at the injury site are likely to exert additional effects in these remote regions. We previously reported that a toll-like receptor 9 (TLR9) antagonist, oligodeoxynucleotide 2088 (ODN 2088), improves functional deficits and modulates the milieu at the epicenter in mice sustaining a mid-thoracic contusion. The present investigations use the same paradigm to assess ODN 2088-elicited alterations in the lumbar dorsal horn (LDH), a region remote from the injury site where SCI-induced molecular alterations have been well defined. We report that ODN 2088 counteracts the SCI-elicited decrease in glial glutamate aspartate transporter (GLAST) and glutamate transporter 1 (GLT1) levels, whereas the levels of the neuronal glutamate transporter excitatory amino acid carrier 1 (EAAC1) and astroglial GABA transporter 3 (GAT3) were unaffected. The restoration of GLAST and GLT1 was neither paralleled by a global effect on astrocyte and microglia activation nor by changes in the expression of cytokines and growth factors reported to regulate these transporters. We conclude that the effects of intrathecal ODN 2088 treatment extend to loci beyond the epicenter by selectively targeting glial glutamate transporters.

Upregulation of calcium channel alpha-2-delta-1 subunit in dorsal horn contributes to spinal cord injury-induced tactile allodynia

BACKGROUND CONTEXT

Spinal cord injury (SCI) commonly results not only in motor paralysis but also in the emergence of neuropathic pain (NeuP), both of which can impair the quality of life for patients with SCI. In the clinical field, it is well known that pregabalin, which binds to the voltage-gated calcium channel alpha-2-delta-1 (α₂δ-1) subunit has therapeutic effects on NeuP after SCI. A previous study has demonstrated that SCI increased α₂δ-1 in the L4-L6 dorsal spinal cord of SCI rats by Western blot analysis and that the increase of α₂δ-1 was correlated with tactile allodynia of the hind paw. However, the detailed feature of an increase in α₂δ-1 protein in the spinal dorsal horn and the mechanism of pregabalin effect on SCI-induced NeuP have not been fully examined.

PURPOSE

This study aimed to examine the detailed distribution of α₂δ-1 expression in the lumbar spinal cord after thoracic SCI in rats and the correlation of the therapeutic effect of pregabalin in SCI rats.

STUDY DESIGN

Male Sprague-Dawley rats underwent thoracic (T10) spinal cord contusion injury using the IH impactor device. Spinal cord injury rats received pregabalin (30 mg/kg) once a day for 2 weeks over a 4-week period after SCI.

METHODS

The mechanical threshold in the rat hind paw was measured over 4 weeks. Alpha-2-delta-1 expression in the lumbar spinal cord and in the dorsal root ganglion (DRG) was analyzed using immunohistochemistry and in situ hybridization histochemistry.

RESULTS

A significant reduction of the withdrawal threshold of mechanical stimuli to the hind paw was observed for 2 weeks and continued at least 4 weeks after SCI. In the control rats, expression of α₂δ-1 immunoreactivity was detected mainly in laminae I and II in the lumbar dorsal horn. Thoracic SCI significantly increased α₂δ-1 immunoreactivity in laminae I and II in the lumbar dorsal horn 4 weeks after SCI; however, thoracic SCI did not affect the expression of α₂δ-1 mRNA in the L4 and L5 DRGs. Meanwhile, the signal intensity of α₂δ-1 mRNAs in the lumbar spinal cord increased from Day 7 and continued for at least 28 days after SCI. Cellular analysis showed that SCI increased the number of α₂δ-1-expressing cells in laminae I and II. The tactile allodynia of the hind paw in the SCI rats was reversed after pregabalin treatment and was maintained for 21 days. This administration of pregabalin decreased the α₂δ-1 immunoreactivity significantly in the lumbar dorsal horn of thoracic SCI rats at 28 days after SCI.

CONCLUSIONS

The present study results suggest that an increase of α₂δ-1 in the L4 and L5 dorsal horns after thoracic SCI is derived from the increase in the expression in lumbar spinal neurons. This increase may be involved in the development of NeuP in the hind paws and the therapeutic effect of pregabalin on central NeuP after SCI.

Activation of spinal dorsal horn P2Y13 receptors can promote the expression of IL-1β and IL-6 in rats with diabetic neuropathic pain

Objective

The dorsal horn P2Y₁₃ receptor is involved in the development of pain behavior induced by peripheral nerve injury. It is unclear whether the expression of proinflammatory cytokines interleukin (IL)-1β and IL-6 at the spinal dorsal horn are influenced after the activation of P2Y₁₃ receptor in rats with diabetic neuropathic pain (DNP).

Methods

A rat model of type 1 DNP was induced by intraperitoneal injection of streptozotocin (STZ). We examined the expression of P2Y₁₃ receptor, Iba-1, IL-1β, IL-6, JAK2, STAT3, pTyr₁₃₃₆, and pTyr₁₄₇₂ NR2B in rat spinal dorsal horn.

Results

Compared with normal rats, STZ-diabetic rats displayed obvious mechanical allodynia and the increased expression of P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 in the dorsal spinal cord that was continued for 6 weeks in DNP rats. The data obtained indicated that, in DNP rats, administration of MRS2211 significantly attenuated mechanical allodynia. Compared with DNP rats, after MRS2211 treatment, expression of the P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 were reduced 4 weeks after the STZ injection. However, MRS2211 treatment did not attenuate the expression of the P2Y₁₃ receptor, Iba-1, IL-1β, and IL-6 at 6 weeks after the STZ injection. MRS2211 suppressed JAK2 and STAT3 expression in the early stage, but not in the later stage. Moreover, pTyr₁₃₃₆ NR2B was significantly decreased, whereas pTyr₁₄₇₂ NR2B was unaffected in the dorsal spinal cord of MRS2211-treated DNP rats.

Conclusion

Intrathecal MRS2211 produces an anti-nociceptive effect in early-stage DNP. A possible mechanism involved in MRS2211-induced analgesia is that blocking the P2Y₁₃ receptor downregulates levels of IL-1β and IL-6, which subsequently inhibit the activation of the JAK2/STAT3 signaling pathway. Furthermore, blocking the activation of the P2Y₁₃ receptor can decrease NR2B-containing NMDAR phosphorylation in dorsal spinal cord neurons, thereby attenuating central sensitization in STZ-induced DNP rats.

Neuregulin-1 elicits a regulatory immune response following traumatic spinal cord injury

Background

Spinal cord injury (SCI) triggers a robust neuroinflammatory response that governs secondary injury mechanisms with both degenerative and pro-regenerative effects. Identifying new immunomodulatory therapies to promote the supportive aspect of immune response is critically needed for the treatment of SCI. We previously demonstrated that SCI results in acute and permanent depletion of the neuronally derived Neuregulin-1 (Nrg-1) in the spinal cord. Increasing the dysregulated level of Nrg-1 through acute intrathecal Nrg-1 treatment enhanced endogenous cell replacement and promoted white matter preservation and functional recovery in rat SCI. Moreover, we identified a neuroprotective role for Nrg-1 in moderating the activity of resident astrocytes and microglia following injury. To date, the impact of Nrg-1 on immune response in SCI has not yet been investigated. In this study, we elucidated the effect of systemic Nrg-1 therapy on the recruitment and function of macrophages, T cells, and B cells, three major leukocyte populations involved in neuroinflammatory processes following SCI.

Methods

We utilized a clinically relevant model of moderately severe compressive SCI in female Sprague-Dawley rats. Nrg-1 (2 μg/day) or saline was delivered subcutaneously through osmotic mini-pumps starting 30 min after SCI. We conducted flow cytometry, quantitative real-time PCR, and immunohistochemistry at acute, subacute, and chronic stages of SCI to investigate the effects of Nrg-1 treatment on systemic and spinal cord immune response as well as cytokine, chemokine, and antibody production.

Results

We provide novel evidence that Nrg-1 promotes a pro-regenerative immune response after SCI. Bioavailability of Nrg-1 stimulated a regulatory phenotype in T and B cells and augmented the population of M2 macrophages in the spinal cord and blood during the acute and chronic stages of SCI. Importantly, Nrg-1 fostered a more balanced microenvironment in the injured spinal cord by attenuating antibody deposition and expression of pro-inflammatory cytokines and chemokines while upregulating pro-regenerative mediators.

Conclusion

We provide the first evidence of a significant regulatory role for Nrg-1 in neuroinflammation after SCI. Importantly, the present study establishes the promise of systemic Nrg-1 treatment as a candidate immunotherapy for traumatic SCI and other CNS neuroinflammatory conditions.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1093-9) contains supplementary material, which is available to authorized users.

Targeting cytokines for treatment of neuropathic pain

BACKGROUND

Neuropathic pain is a challenging condition often refractory to existing therapies. An increasing number of studies have indicated that the immune system plays a crucial role in the mediation of neuropathic pain. Exploration of the various functions of individual cytokines in neuropathic pain will provide greater insight into the mechanisms of neuropathic pain and suggest potential opportunities to expand the repertoire of treatment options.

METHODS

A literature review was performed to assess the role of pro-inflammatory and anti-inflammatory cytokines in the development of neuropathic pain. Both direct and indirect therapeutic approaches that target various cytokines for pain were reviewed. The current understanding based on preclinical and clinical studies is summarized.

RESULTS AND CONCLUSIONS

In both human and animal studies, neuropathic pain has been associated with a pro-inflammatory state. Analgesic therapies involving direct manipulation of various cytokines and indirect methods to alter the balance of the immune system have been explored, although there have been few large-scale clinical trials evaluating the efficacy of immune modulators in the treatment of neuropathic pain. TNF-α is perhaps the widely studied pro-inflammatory cytokine in the context of neuropathic pain, but other pro-inflammatory (IL-1β, IL-6, and IL-17) and anti-inflammatory (IL-4, IL-10, TGF-β) signaling molecules are garnering increased interest. With better appreciation and understanding of the interaction between the immune system and neuropathic pain, novel therapies may be developed to target this condition.

Involvement of Spinal IL-6 Trans-Signaling in the Induction of Hyperexcitability of Deep Dorsal Horn Neurons by Spinal Tumor Necrosis Factor-Alpha

During peripheral inflammation, both spinal TNF-α and IL-6 are released within the spinal cord and support the generation of inflammation-evoked spinal hyperexcitability. However, whether spinal TNF-α and IL-6 act independently in parallel or in a functionally dependent manner has not been investigated. In extracellular recordings from mechanonociceptive deep dorsal horn neurons of normal rats in vivo, we found that spinal application of TNF-α increased spinal neuronal responses to mechanical stimulation of knee and ankle joints. This effect was significantly attenuated by either sgp130, which blocks IL-6 trans-signaling mediated by IL-6 and its soluble receptor IL-6R (sIL-6R); by an antibody to the IL-6 receptor; or by minocycline, which inhibits the microglia. IL-6 was localized in neurons of the spinal cord and, upon peripheral noxious stimulation in the presence of spinal TNF-α, IL-6 was released spinally. Furthermore, TNF-α recruited microglial cells to provide sIL-6R, which can form complexes with IL-6. Spinal application of IL-6 plus sIL-6R, but not of IL-6 alone, enhanced spinal hyperexcitability similar to TNF-α and the inhibition of TNF-α-induced hyperexcitability by minocycline was overcome by coadministration of sIL-6R, showing that sIL-6R is required. Neither minocycline nor the TNF-α-neutralizing compound etanercept inhibited the induction of hyperexcitability by IL-6 plus sIL-6R. Together, these data show that the induction of hyperexcitability of nociceptive deep dorsal horn neurons by TNF-α largely depends on the formation of IL-6/sIL-6R complexes that are downstream of TNF-α and requires the interactions of neurons and microglia orchestrated by TNF-α.

SIGNIFICANCE STATEMENT

Both spinal TNF-α and IL-6 induce a state of spinal hyperexcitability. We present the novel finding that the full effect of TNF-α on the development of spinal hyperexcitability depends on IL-6 trans-signaling acting downstream of TNF-α. IL-6 trans-signaling requires the formation of complexes of IL-6 and soluble IL-6 receptor. Spinal TNF-α furthers the release of IL-6 from neurons in the spinal cord during peripheral noxious stimulation and recruits microglial cells to provide soluble IL-6 receptor, which can form complexes with IL-6. Therefore, a specific interaction between neurons and microglia is required for the full development of TNF-α-induced hyperexcitability of nociceptive deep horsal horn neurons.

Inhibition of interleukin-6 function attenuates the central sensitization and pain behavior induced by osteoarthritis

Chronic pain is the most prominent and disabling symptom in the patients with osteoarthritis (OA), and the underlying mechanism largely remains unclear. Interleukin-6 (IL-6), a proinflammatory cytokine, is critically involved in the development and maintenance of central sensitization in several rodent models of chronic pain. The present study aims to elucidate the IL-6 mediated neurological adaptation in dorsal horn in the rat with monosodium iodoacetate (MIA) - induced OA. Significant upregulation of IL-6 expression was detected in the dorsal horn in the modeled rats. Blockade of IL-6 function by tocilizumab markedly suppressed the activation of astrocytes and microglia in the ipsilateral dorsal horn, reduced c-Fos immunoreactivity in dorsal horn neurons, and attenuated the upregulation of glutamate receptor subunits GluR1 and NR2B in dorsal horn in the rats with MIA-induced OA. It was further reported that administration of tocilizumab significantly improved the performance in weight-bearing test and mitigated the mechanical allodynia in the modeled rats. These data illustrated spinal IL-6 mediated mechanism underlying the chronic pain, and proposed the potential therapeutic effect of tocilizumab on the chronic pain in the setting of OA.

Niclosamide Inhibits Oxaliplatin Neurotoxicity while Improving Colorectal Cancer Therapeutic Response

Neuropathic pain is a limiting factor of platinum-based chemotherapies. We sought to investigate the neuroprotective potential of niclosamide in peripheral neuropathies induced by oxaliplatin. Normal neuron-like and cancer cells were treated in vitro with oxaliplatin associated or not with an inhibitor of STAT3 and NF-κB, niclosamide. Cell production of reactive oxygen species and viability were measured by 2',7'-dichlorodihydrofluorescein diacetate and crystal violet. Peripheral neuropathies were induced in mice by oxaliplatin with or without niclosamide. Neurologic functions were assessed by behavioral and electrophysiologic tests, intraepidermal innervation, and myelination by immunohistochemical, histologic, and morphologic studies using confocal microscopy. Efficacy on tumor growth was assessed in mice grafted with CT26 colon cancer cells. In neuron-like cells, niclosamide downregulated the production of oxaliplatin-mediated H₂O₂, thereby preventing cell death. In colon cancer cells, niclosamide enhanced oxaliplatin-mediated cell death through increased H₂O₂ production. These observations were explained by inherent lower basal levels of GSH in cancer cells compared with normal and neuron-like cells. In neuropathic mice, niclosamide prevented tactile hypoesthesia and thermal hyperalgesia and abrogated membrane hyperexcitability. The teniacide also prevented intraepidermal nerve fiber density reduction and demyelination in oxaliplatin mice in this mixed form of peripheral neuropathy. Niclosamide prevents oxaliplatin-induced increased levels of IL6, TNFα, and advanced oxidized protein products. Niclosamide displayed antitumor effects while not abrogating oxaliplatin efficacy. These results indicate that niclosamide exerts its neuroprotection both in vitro and in vivo by limiting oxaliplatin-induced oxidative stress and neuroinflammation. These findings identify niclosamide as a promising therapeutic adjunct to oxaliplatin chemotherapy. Mol Cancer Ther; 16(2); 300-11. ©2016 AACR.

Macrophagic control of the response to uropathogenic E. coli infection by regulation of iron retention in an IL-6-dependent manner

Introduction

Uropathogenic Escherichia coli (UPEC), the causative agent of over 85% of urinary tract infections (UTIs), elaborate a number of siderophores to chelate iron from the host. On the other hand, the host immune imperative is to limit the availability of iron to the bacteria. Little is known regarding the mechanisms underlying this host‐iron‐UPEC interaction. Our objective was to determine whether macrophages, in response to UPEC infection, retain extracellular siderophore‐bound and free iron, thus limiting the ability of UPEC to access iron.

Methods

Quantitative PCR, immunoblotting analysis, and gene expression analysis of wild type and IL‐6‐deficient macrophages was performed.

Results

We found that (1) macrophages upon UPEC infection increased expression of lipocalin 2, a siderophore‐binding molecule, of Dmt1, a molecule that facilitates macrophage uptake of free iron, and of the intracellular iron cargo molecule ferritin, and decreased expression of the iron exporter ferroportin; (2) bladder macrophages regulate expression of genes involved in iron retention upon UPEC infection; (3) IL‐6, a cytokine known to play an important role in regulating host iron homeostasis as well as host defense to UPEC, regulates this process, in part by promoting production of lipocalin 2; and finally, (4) inhibition of IL‐6 signaling genetically and by neutralizing antibodies against the IL‐6 receptor, promoted intra‐macrophagic UPEC growth in the presence of excess iron.

Conclusions

Together, our study suggests that macrophages retain siderophore‐bound and free iron in response to UPEC and IL‐6 signaling is necessary for macrophages to limit the growth of UPEC in the presence of excess iron. IL‐6 signaling and iron regulation is one mechanism by which macrophages may mediate UPEC clearance.

Toll like receptor 9 antagonism modulates spinal cord neuronal function and survival: Direct versus astrocyte-mediated mechanisms

Toll like receptors (TLRs) are expressed by cells of the immune system and mediate the host innate immune responses to pathogens. However, increasing evidence indicates that they are important contributors to central nervous system (CNS) function in health and in pathological conditions involving sterile inflammation. In agreement with this idea, we have previously shown that intrathecal administration of a TLR9 antagonist, cytidine-phosphate-guanosine oligodeoxynucleotide 2088 (CpG ODN 2088), ameliorates the outcomes of spinal cord injury (SCI). Although these earlier studies showed a marked effect of CpG ODN 2088 on inflammatory cells, the expression of TLR9 in spinal cord (SC) neurons and astrocytes suggested that the antagonist exerts additional effects through direct actions on these cells. The current study was undertaken to assess the direct effects of CpG ODN 2088 on SC neurons, astrocytes and astrocyte-neuron interactions, in vitro. We report, for the first time, that inhibition of TLR9 in cultured SC neurons alters their function and confers protection against kainic acid (KA)-induced excitotoxic death. Moreover, the TLR9 antagonist attenuated the KA-elicited endoplasmic reticulum (ER) stress response in neurons, in vitro. CpG ODN 2088 also reduced the transcript levels and release of chemokine (C-X-C) motif ligand 1 (CXCL1) and monocyte chemotactic protein 1 (MCP-1) by astrocytes and it diminished interleukin-6 (IL-6) release without affecting transcript levels in vitro. Conditioned medium (CM) of CpG ODN 2088-treated astroglial cultures decreased the viability of SC neurons compared to CM of vehicle-treated astrocytes. However, this toxicity was not observed when astrocytes were co-cultured with neurons. Although CpG ODN 2088 limited the survival-promoting effects of astroglia, it did not reduce neuronal viability compared to controls grown in the absence of astrocytes. We conclude that the TLR9 antagonist acts directly on both SC neurons and astrocytes. Neuronal TLR9 antagonism confers protection against excitotoxic death. It is likely that this neuroprotection is partly due to the attenuation of the ER stress response provoked by excitotoxicity. Although CpG ODN 2088 limits the supportive effects of astrocytes on neurons, it could potentially exert beneficial effects by decreasing the release of pro-inflammatory cytokines and chemokines by astroglia. These findings highlight the multiple roles of TLR9 in the SC and have implications for pathological conditions including SCI where excitotoxicity and neuroinflammation play a prominent role in neuronal degeneration.

Tocilizumab's effect on cognitive deficits induced by intracerebroventricular administration of streptozotocin in Alzheimer's model

Neuroinflammation plays pivotal roles in the pathogenesis of Alzheimer's disease (AD). IL-6 is pleiotropic cytokine which plays significant pathological role in inflammatory diseases and causes prolonged inflammation. Additionally, IL-6 activates microglia cells and enhances the accumulation of amyloid-β peptides. Moreover, IL-6 signal transduction is mediated by membrane-bound and soluble IL-6 receptors. Tocilizumab which is a humanized anti-human IL-6 receptor (IL-6R) monoclonal antibody binds to both of these receptors and inhibits IL-6 signaling by this route. The objective was to investigate tocilizumab's potential effects in the treatment of AD. Male Sprague-Dawley rats were divided into three groups: sham (control), streptozotocin (STZ), and tocilizumab-STZ. We used a single dose of intracerebroventricular (ICV) tocilizumab, beginning 1 h prior to injection of STZ for 3 weeks. The rats in STZ and tocilizumab-STZ groups were given ICV-STZ (3 mg/kg). Behavioral parameters were evaluated on days 17-20 and the rats were sacrificed on day-21 to examine histopathological changes. STZ injection caused significant decrease in the mean escape latency in passive avoidance and also declined the performance improvement in Morris water maze tests. Tocilizumab-STZ group significantly improved learning and spatial memory functions by increasing RLT in the passive avoidance and by shortening escape latency in reaching the platform in the Morris water maze. Histopathological changes were examined using hematoxylin and eosin and immunohistochemical (IHC) stainings. IHC analysis revealed that while protein expressions of amyloid-ß (3.5 ± 0.2) and IL-6 (2.9 ± 0.4) showed intense immune-positivity in STZ group, amyloid-ß (1.3 ± 0.1) and IL-6 (1.5 ± 0.2) immunoreactivities were substantially decreased in tocilizumab treatment group. We conclude that tocilizumab treatment attenuated significantly STZ-induced cognitive impairment and histopathological changes. Further studies would be desirable to investigate clinically relevant protective effects of tocilizumab in AD.