Down-Regulation of CXCL12/CXCR4 Expression Alleviates Ischemia-Reperfusion-Induced Inflammatory Pain via Inhibiting Glial TLR4 Activation in the Spinal Cord

Aitongping patch could alleviate cancer pain via suppressing microglia activation and modulating the miR-150-5p/CXCL12 signaling

PURPOSE

We aimed to investigate the pharmacological effects and mechanisms of the Aitongping formula for treating cancer pain.

METHODS

We enrolled 60 cancer patients with Numeric Rating Scale above 4 and grouped them randomly as a Control group (N = 30) and a Patch group (N = 30). We also established bone cancer mice models via tumor implantation. And the animal groups were established as a Sham group, a tumor cell implantation (TCI) group, a TCI + Patch group, and a Patch group.

RESULTS

After the validation of successful tumor implantation, we identified candidate miRNAs and genes that were dysregulated in TCI mice and compared their expressions between different mice groups. We also observed the effect of Aitongping patch in vitro in mice primary microglia. The time to disease progression and cancer stability were prolonged by Aitongping patch in cancer patients. And the daily morphine dose was lower, and patients' quality of life was improved in the Patch group. Moreover, Aitongping patch alleviated cancer pain and inhibited microglia activation after the successful implantation of bone tumor in TCI mice. We also observed the dysregulation of miR-150-5p and chemokine CXC motif ligand 12 (CXCL12) mRNA in TCI mice. And CXCL12 was found to be targeted by miR-150-5p. Aitongping patch was found to upregulate miR-150-5p and downregulate CXCL12 in vivo and in vitro.

CONCLUSION

Aitongping patch could alleviate cancer pain via suppressing microglia activation, and the downregulation of miR-150-5p, as well as the upregulation of CXCL12 mRNA and protein, induced by tumor implantation or lipopolysaccharide stimulation, was restored by Aitongping treatment.

Esketamine inhibits the c-Jun N-terminal kinase pathway in the spinal dorsal horn to relieve bone cancer pain in rats

Cancer-induced bone pain (CIBP) is one of the most common and feared symptoms in patients with advanced tumors. The X-C motif chemokine ligand 12 (CXCL12) and the CXCR4 receptor have been associated with glial cell activation in bone cancer pain. Moreover, mitogen-activated protein kinases (MAPKs), as downstream CXCL12/CXCR4 signals, and c-Jun, as activator protein AP-1 components, contribute to the development of various types of pain. However, the specific CIBP mechanisms remain unknown. Esketamine is a non-selective N-methyl-d-aspartic acid receptor (NMDA) inhibitor commonly used as an analgesic in the clinic, but its analgesic mechanism in bone cancer pain remains unclear. We used a tumor cell implantation (TCI) model and explored that CXCL12/CXCR4, p-MAPKs, and p-c-Jun were stably up-regulated in the spinal cord. Immunofluorescence images showed activated microglia in the spinal cord on day 14 after TCI and co-expression of CXCL12/CXCR4, p-MAPKs (p-JNK, p-ERK, p-p38 MAPK), and p-c-Jun in microglia. Intrathecal injection of the CXCR4 inhibitor AMD3100 reduced JNK and c-Jun phosphorylations, and intrathecal injection of the JNK inhibitor SP600125 and esketamine also alleviated TCI-induced pain and reduced the expression of p-JNK and p-c-Jun in microglia. Overall, our data suggest that the CXCL12/CXCR4-JNK-c-Jun signaling pathway of microglia in the spinal cord mediates neuronal sensitization and pain hypersensitivity in cancer-induced bone pain and that esketamine exerts its analgesic effect by inhibiting the JNK-c-Jun pathway.

Knockdown of PAC1 improved inflammatory pain in mice by regulating the RAGE/TLR4/NF-κB signaling pathway

The development of inflammatory pain seriously affects the activities and general functions of patients in daily life. At present, the research on the mechanism of pain relief is still insufficient. This study aimed to investigate the influence of PAC1 on the progression of inflammatory pain and its molecular mechanism. Lipopolysaccharide (LPS) was used to induce BV2 microglia activation to establish an inflammation model, and CFA injection was used to establish a mouse inflammatory pain model. The results showed that PAC1 was highly expressed in BV2 microglia induced by LPS. Knockdown of PAC1 significantly reduced LPS-induced inflammation and apoptosis in BV2 cells, and RAGE/TLR4/NF-κB signaling pathway was involved in the regulation of BV2 cells by PAC1. What's more, knockdown of PAC1 alleviated CFA-induced mechanical allodynia and thermal hyperalgesia in mice, as well as reduced the development of inflammatory pain to a certain extent. Therefore, Knockdown of PAC1 relieved inflammatory pain in mice by inhibiting the RAGE/TLR4/NF-κB signaling pathway. Targeting PAC1 may be a new direction for the treatment of inflammatory pain.

Electroacupuncture Attenuates Fibromyalgia Pain via Toll-like Receptor 4 in the Mouse Brain

BACKGROUND

Fibromyalgia (FM) is characterized by complex pain symptoms lacking impersonal considerations in diagnosis and treatment evaluation, which often happens in women. Chronic and persistent widespread pain is the key symptom disturbing patients with FM, leading to depression, obesity, and sleep disturbances. Toll-like receptor 4 (TLR4) activation produces a harmful sensory input involved in central pain; this is the focus of this study. Electroacupuncture (EA) has beneficial effects in reducing FM pain, but its connection with TLR4 signaling is still unknown.

METHODS

Intermittent cold stress significantly induced mechanical and thermal pain. EA, but not sham EA, reliably attenuated mechanical and thermal hyperalgesia. The increased inflammatory mediators in FM mice were reduced in the EA group, but not in the sham group.

RESULTS

All TLR4 and related molecule levels increased in the FM mice's hypothalamus, periaqueductal gray (PAG), and cerebellum. These increases could be attenuated by EA but not sham stimulation. Activation of TLR4 by lipopolysaccharide (LPS) significantly induced FM and can be further reversed by a TLR4 antagonist.

CONCLUSIONS

These mechanisms provide evidence that the analgesic effect of EA is related to the TLR4 pathway. In addition, we showed that inflammation can activate the TLR4 pathway and provided new possible therapeutic targets for FM pain.

MicroRNA: Crucial modulator in purinergic signalling involved diseases

Both microRNAs (miRNAs) and purinergic signalling are widely and respectively expressed in various tissues of different organisms and play vital roles in a variety of physiological and pathological processes. Here, we reviewed the current publications contributed to the relationship of miRNAs and purinergic signalling in cardiovascular diseases, gastrointestinal diseases, neurological diseases, and ophthalmic diseases. We tried to decode the miRNAs-purinergic signalling network of purinergic signalling involved diseases. The evidence indicated that more than 30 miRNAs (miR-22, miR-30, miR-146, miR-150, miR-155, miR-187, etc.) directly or indirectly modulate P1 receptors (A₁, A_2A, A_2B, A₃), P2 receptors (P2X1, P2X3, P2X4, P2X7, P2Y2, P2Y6, P2Y12), and ecto-enzymes (CD39, CD73, ADA2); P2X7 and CD73 could be modulated by multiple miRNAs (P2X7: miR-21, miR-22, miR-30, miR-135a, miR-150, miR-186, miR-187, miR-216b; CD73: miR-141, miR-101, miR-193b, miR-340, miR-187, miR-30, miR-422a); miR-187 would be the common miRNA to modulate P2X7 and CD73.

Secondary damage and neuroinflammation in the spinal dorsal horn mediate post-thalamic hemorrhagic stroke pain hypersensitivity: SDF1-CXCR4 signaling mediation

Central post-stroke pain (CPSP) is an intractable neuropathic pain, which can be caused by primary lesion of central somatosensory system. It is also a common sequelae of the thalamic hemorrhagic stroke (THS). So far, the underlying mechanisms of CPSP remain largely unknown. Our previous studies have demonstrated that SDF1-CXCR4 signaling in the hemorrhagic region contributes to the maintenance of the THS pain hypersensitivity via mediation of the thalamic neuroinflammation. But whether the spinal dorsal horn, an initial point of spinothalamic tract (STT), suffers from retrograde axonal degeneration from the THS region is still unknown. In this study, neuronal degeneration and loss in the spinal dorsal horn were detected 7 days after the THS caused by intra-thalamic collagenase (ITC) injection by immunohistochemistry, TUNEL staining, electron microscopy, and extracellular multi-electrode array (MEA) recordings, suggesting the occurrence of secondary apoptosis and death of the STT projecting neuronal cell bodies following primary THS via retrograde axonal degeneration. This retrograde degeneration was accompanied by secondary neuroinflammation characterized by an activation of microglial and astrocytic cells and upregulation of SDF1-CXCR4 signaling in the spinal dorsal horn. As a consequence, central sensitization was detected by extracellular MEA recordings of the spinal dorsal horn neurons, characterized by hyperexcitability of both wide dynamic range and nociceptive specific neurons to suprathreshold mechanical stimuli. Finally, it was shown that suppression of spinal neuroinflammation by intrathecal administration of inhibitors of microglia (minocycline) and astrocytes (fluorocitrate) and antagonist of CXCR4 (AMD3100) could block the increase in expression levels of Iba-1, GFAP, SDF1, and CXCR4 proteins in the dorsal spinal cord and ameliorate the THS-induced bilateral mechanical pain hypersensitivity, implicating that, besides the primary damage at the thalamus, spinal secondary damage and neuroinflammation also play the important roles in maintaining the central post-THS pain hypersensitivity. In conclusion, secondary neuronal death and neuroinflammation in the spinal dorsal horn can be induced by primary thalamic neural damage via retrograde axonal degeneration process. SDF1-CXCR4 signaling is involved in the mediation of secondary spinal neuroinflammation and THS pain hypersensitivity. This finding would provide a new therapeutic target for treatment of CPSP at the spinal level.

3D Bioprinted Neural-Like Tissue as a Platform to Study Neurotropism of Mouse-Adapted SARS-CoV-2

The effects of neuroinvasion by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) become clinically relevant due to the numerous neurological symptoms observed in Corona Virus Disease 2019 (COVID-19) patients during infection and post-COVID syndrome or long COVID. This study reports the biofabrication of a 3D bioprinted neural-like tissue as a proof-of-concept platform for a more representative study of SARS-CoV-2 brain infection. Bioink is optimized regarding its biophysical properties and is mixed with murine neural cells to construct a 3D model of COVID-19 infection. Aiming to increase the specificity to murine cells, SARS-CoV-2 is mouse-adapted (MA-SARS-CoV-2) in vitro, in a protocol first reported here. MA-SARS-CoV-2 reveals mutations located at the Orf1a and Orf3a domains and is evolutionarily closer to the original Wuhan SARS-CoV-2 strain than SARS-CoV-2 used for adaptation. Remarkably, MA-SARS-CoV-2 shows high specificity to murine cells, which present distinct responses when cultured in 2D and 3D systems, regarding cell morphology, neuroinflammation, and virus titration. MA-SARS-CoV-2 represents a valuable tool in studies using animal models, and the 3D neural-like tissue serves as a powerful in vitro platform for modeling brain infection, contributing to the development of antivirals and new treatments for COVID-19.

Drug Discovery in Spinal Cord Injury With Ankylosing Spondylitis Identified by Text Mining and Biomedical Databases

Spinal cord injury (SCI) and ankylosing spondylitis (AS) are common inflammatory diseases in spine surgery. However, it is a project where the relationship between the two diseases is ambiguous and the efficiency of drug discovery is limited. Therefore, the study aimed to investigate new drug therapies for SCI and AS. First, text mining was used to obtain the interacting genes related to SCI and AS, and then, the functional analysis was conducted. Protein–protein interaction (PPI) networks were constructed by STRING online and Cytoscape software to identify hub genes. Last, hub genes and potential drugs were performed after undergoing drug–gene interaction analysis, and MicroRNA and transcription factors regulatory networks were also analyzed. Two hundred five genes common to “SCI” and “AS” identified by text mining were enriched in inflammatory responses. PPI network analysis showed that 30 genes constructed two significant modules. Ultimately, nine (SST, VWF, IL1B, IL6, CXCR4, VEGFA, SERPINE1, FN1, and PROS1) out of 30 genes could be targetable by a total of 13 drugs. In conclusion, the novel core genes contribute to a novel insight for latent functional mechanisms and present potential prognostic indicators and therapeutic targets in SCI and AS.

Toll-Like Receptor 4 in Pain: Bridging Molecules-to-Cells-to-Systems

Pain impacts the lives of billions of people around the world - both directly and indirectly. It is complex and transcends beyond an unpleasant sensory experience to encompass emotional experiences. To date, there are no successful treatments for sufferers of chronic pain. Although opioids do not provide any benefit to chronic pain sufferers, they are still prescribed, often resulting in more complications such as hyperalgesia and dependence. In order to develop effective and safe medications to manage, and perhaps even treat pain, it is important to evaluate novel contributors to pain pathologies. As such, in this chapter we review the role of Toll-like receptor 4, a receptor of the innate immune system, that continues to gain substantial attention in the field of pain research. Positioned in the nexus of the neuro and immune systems, TLR4 may provide one of the missing pieces in understanding the complexities of pain. Here we consider how TLR4 enables a mechanistical understanding of pain as a multidimensional biopsychosocial state from molecules to cells to systems and back again.

lncRNA MEG3 aggravated neuropathic pain and astrocyte overaction through mediating miR-130a-5p/CXCL12/CXCR4 axis

OBJECTIVE

Long non-coding RNAs (lncRNAs) exert a critical function in mediating neuropathic pain (NP). MEG3, a novel lncRNA, contributes to astrocyte activation and inflammation. However, its role in NP remains unclear.

METHODS

The chronic constriction injury (CCI) method was employed to construct an NP rat model. Astrocyte activation was induced by lipopolysaccharide (LPS). The profiles of MEG3, microRNA (miR)-130a-5p, CXC motif chemokine receptor 12 (CXCL12)/CXC motif chemokine receptor 4 (CXCR4), and the Rac1/NF-κB pathway in CCI rats' spinal cord tissues and astrocytes were monitored by reverse transcription-quantitative PCR (RT-qPCR) and western blot (WB). Pain scores of CCI rats were assessed. Enzyme-linked immunosorbent assay (ELISA) was adopted to monitor neuroinflammation alteration. The glial fibrillary acidic protein (GFAP)-labeled astrocytes were tested by immunohistochemistry (IHC). Bioinformatics, dual-luciferase reporter assay and RNA immunoprecipitation (RIP) were utilized to verify the molecular mechanism between MEG3 and miR-130a-3p.

RESULTS

MEG3, CXCL12 and CXCR4 were overexpressed and miR-130a-5p was knocked down in CCI rats and LPS-induced astrocytes. Up-regulating MEG3 aggravated NP, enhanced inflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor (TNF)-α, and interleukin-6 (IL-6) expression and release in CCI rats and LPS-induced astrocytes. Up-regulating miR-130-5p repressed LPS-induced inflammation in astrocytes. AS verified by the dual-luciferase reporter assay and RIP assay, MEG3 sponged miR-130a-5p as a competitive endogenous RNA (ceRNA). What's more, miR-130a-5p up-regulation weakened the MEG3-induced proinflammatory effects on LPS-induced astrocytes.

CONCLUSIONS

MEG3 aggravates NP and astrocyte activation via the miR-130a-5p/CXCL12/CXCR4 axis, which is a potential therapeutic target for NP.

Blocking receptor for advanced glycation end products (RAGE) or toll-like receptor 4 (TLR4) prevents posttraumatic epileptogenesis in mice

OBJECTIVE

Effective treatment for the prevention of posttraumatic epilepsy is still not available. Here, we sought to determine whether blocking receptor for advanced glycation end products (RAGE) or toll-like receptor 4 (TLR4) signaling pathways would prevent posttraumatic epileptogenesis.

METHODS

In a mouse undercut model of posttraumatic epilepsy, daily injections of saline, RAGE monoclonal antibody (mAb), or TAK242, a TLR4 inhibitor, were made for 1 week. Their effects on seizure susceptibility and spontaneous epileptic seizures were evaluated with a pentylenetetrazol (PTZ) test in 2 weeks and with continuous video and wireless electroencephalography (EEG) monitoring between 2 and 6 weeks after injury, respectively. Seizure susceptibility after undercut in RAGE knockout mice was also evaluated with the PTZ test. The lesioned cortex was analyzed with immunohistology.

RESULTS

Undercut animals treated with RAGE mAb or TAK242 showed significantly higher seizure threshold than saline-treated undercut mice. Consistently, undercut injury in RAGE knockout mice did not cause a reduction in seizure threshold in the PTZ test. EEG and video recordings revealed a significant decrease in the cumulative spontaneous seizure events in the RAGE mAb- or TAK242-treated group (p < 0.001, when the RAGE mAb or TAK242 group is compared with the saline group). The lesioned cortical tissues of RAGE mAb- or TAK242-treated undercut group showed higher neuronal densities of Nissl staining and higher densities of glutamic acid decarboxylase 67-immunoreactive interneurons than the saline-treated undercut group. Immunostaining to GFAP and Iba-1 revealed lower densities of astrocytes and microglia in the cortex of the treatment groups, suggesting reduced glia activation.

SIGNIFICANCE

RAGE and TLR4 signaling are critically involved in posttraumatic epileptogenesis. Blocking these pathways early after traumatic brain injury is a promising strategy for preventing posttraumatic epilepsy.

Subcutaneous Administration of AMD3100 into Mice Models of Alzheimer's Disease Ameliorated Cognitive Impairment, Reduced Neuroinflammation, and Improved Pathophysiological Markers

BACKGROUND

Alzheimer's disease (AD), the prevalent dementia in the elderly, involves many related and interdependent pathologies that manifest simultaneously, leading to cognitive impairment and death. Amyloid-β (Aβ) accumulation in the brain triggers the onset of AD, accompanied by neuroinflammatory response and pathological changes. The CXCR4/CXCL12 (SDF1) axis is one of the major signal transduction cascades involved in the inflammation process and regulation of homing of hematopoietic stem cells (HSCs) within the bone marrow niche. Inhibition of the axis with AMD3100, a reversible antagonist of CXCR4 mobilizes endogenous HSCs from the bone marrow into the periphery, facilitating the recruitment of bone marrow-derived microglia-like cells into the brain, attenuates the neuroinflammation process that involves release of excitotoxic markers such as TNFα, intracellular Ca2 +, and glutamate and upregulates monocarboxylate transporter 1, the major L-lactate transporter in the brain.

OBJECTIVE

Herein, we investigate if administration of a combination of AMD3100 and L-lactate may have beneficial effects in the treatment of AD.

METHODS

We tested the feasibility of the combined treatment for short- and long-term efficacy for inducing endogenous stem cells' mobilization and attenuation of neuroinflammation in two distinct amyloid-β-induced AD mouse models.

RESULTS

The combined treatment did not demonstrate any adverse effects on the mice, and resulted in a significant improvement in cognitive/memory functions, attenuated neuroinflammation, and alleviated AD pathologies compared to each treatment alone.

CONCLUSION

This study showed AMD3100's beneficial effect in ameliorating AD pathogenesis, suggesting an alternative to the multistep procedures of transplantation of stem cells in the treatment of AD.

Mechanism of Cdk5-synaptophysin-SNARE pathway in acute and chronic inflammatory pain

PURPOSE

Currently, there is no favorable treatment plan for inflammatory pain, so exploring new analgesics is still a research hotspot in this area. Cyclin-dependent protein kinase 5 (Cdk5) is a pain-related protein kinase, but its mechanism in inflammatory pain has not been clarified. This research aimed to explore the mechanism of Cdk5-synaptophysin (Syn)-soluble N-ethylmaleimide-sensitivity factor (NSF) attachment protein receptor (SNARE) in acute and chronic inflammatory pain.

METHODS

Rat models of acute and chronic inflammatory pain were induced by formalin and complete Freund's adjuvant (CFA), separately, and some rats injected with normal saline through intraplantar injection were divided into a control group. Thirty minutes before modeling, rats were given Cdk5 inhibitor (Roscovitine, Ros), SNARE scavenger (botulinum toxin A, BTTA), glutamate receptor inhibitor (MK801), and dimethyl sulfoxide (DMSO) through spinal canals, and the paw withdrawal threshold (PWT) and thermal withdrawal latency (PWL) at difference time points were compared.

RESULTS

Compared with rats in the control group, those in the rat models of acute and chronic inflammatory pain showed lower PWT and PWL, higher Cdk5 enzyme level, tight correlation of Cdk5 with Syn, SNARE, p25 proteins, and higher levels of Cdk5, Syn and SNARE. And the above situation was dramatically reversed under intervention of Ros, BTTA and MK801.

CONCLUSION

Cdk5-Syn-SNARE pathway is a therapeutic target for inflammatory pain. Blocking the activation of this pathway is beneficial to exert analgesic effect.

MiR-126-3p-Enriched Extracellular Vesicles from Hypoxia-Preconditioned VSC 4.1 Neurons Attenuate Ischaemia-Reperfusion-Induced Pain Hypersensitivity by Regulating the PIK3R2-Mediated Pathway

Recent evidence suggests that hypoxia preconditioning can alter the microRNA (miRNA) profile of extracellular vesicles (EVs) and has better neuroprotective effects when enriched miRs are delivered to recipients. However, the roles of exosomal miRNAs in regulating ischaemia-reperfusion (IR)-induced pain hypersensitivity are largely unknown. Thus, we isolated EVs from normoxia-conditioned neurons (Nor-VSC EVs) and Hypo-VSC EVs by ultracentrifugation. After the initial screening by a microarray analysis and quantitative RT-PCR (qRT-PCR), miR-126-3p, which was detected as the most altered miR in the Hypo-VSC EVs, was further confirmed by applying GW4869 to inhibit exosomal secretion. Moreover, transfection with a miR-126 mimic obviously increased miR-126-3p expression in Nor-VSC EVs, whereas a miR-126 inhibitor prevented the increase in miR-126-3p in Hypo-VSC EVs. A rat model of pain was established by performing 8-min occlusion of the aorta. Following IR, compared with the Nor-VSC EVs- or antagomir-126-injected rats, the Hypo-VSC EVs-injected rats displayed improved pain hypersensitivity demonstrated as higher PWT and PWL values. Mechanistically, PIK3R2 is a target of miR-126-3p and might be a modulator of the phosphoinositide 3-kinase (PI3K)/Akt pathway as the PIK3R2 and PI3K immunoreactivities in each group were changed in opposite directions. Compared with the controls, higher protein levels of PI3K and phosphorylated Akt but lower levels of phosphorylated nuclear factor-κ B (NF-κB), tumour necrosis factor (TNF)-α and interleukin (IL)-1β were detected in the spinal cords of the Hypo-VSC EVs-injected rats, and these effects were impaired by an injection of Hypo-VSC EVs combined with antagomir-126. Collectively, the miR-126-3p-enriched Hypo-VSC EVs attenuated IR-induced pain hypersensitivity by restoring miR-126-3p expression in the injured spinal cord and subsequently modulating PIK3R2-mediated PI3K/Akt and NF-κB signalling pathways.

Upregulating miR-130a-5p relieves astrocyte over activation-induced neuropathic pain through targeting C-X-C motif chemokine receptor 12/C-X-C motif chemokine receptor 4 axis

OBJECTIVES

This study intends to explore the role and specific mechanism of miR-130a-5p in neuropathic pain through regulating the C-X-C motif chemokine receptor 12 (CXCL12)-C-X-C motif chemokine receptor 4 (CXCR4) pathway.

METHODS

First, mouse neuropathic pain model was constructed by spinal nerve ligation. MiR-130a-5p mimics were used to upregulate miR-130a-5p in vivo. The behaviour and pain scores of the spinal cord injury (SCI) mice were assessed. In addition, astrocytic activation as well as inflammatory response in the spinal lesions was determined.

RESULTS

The results manifested miR-130a-5p was notably downregulated in neuropathic pain model and reached the lowest point at 3 days after injury. Besides, tail vein injection of miR-130a-5p mimics inhibited the activation and inflammatory response of astrocytes, thus alleviating chronic constriction injury-induced neuropathic pain. Moreover, miR-130a-5p inactivated CXCR4 and its downstream Rac1, nuclear factor-κB (NF-κB) and extracellular regulated protein kinases signalling pathways by attenuating CXCL12.

CONCLUSION

MiR-130a-5p inactivated astrocytes by targeting CXCL12/CXCR4, thus alleviating SCI-induced neuropathic pain.

A Review of the Mechanism of Action of Cyclosporine A: The Role of Cyclosporine A in Dry Eye Disease and Recent Formulation Developments

Dry eye disease (DED) is a multifactorial disease of the ocular surface and tear film that has gained awareness as a public health problem. Characteristics of DED include tear film instability, hyperosmolarity, and ocular surface inflammation, which can occur independently or may be a sequela of numerous ocular diseases, ocular surgery or contact lens wear. Much has been learned about the impact of the disease to help affected individuals who report symptoms of poor vision, pain, and tearing. Recently, new research highlights the importance of the role of ocular surface inflammation and damage in DED-leading to a vicious cycle of inflammation as well as loss of tear film homeostasis. DED immunopathophysiology is characterized by four stages: initiation, amplification, recruitment, and re-initiation. Cyclosporine is proven to be a valuable ophthalmic therapeutic for DED through its immunomodulatory actions and regulation of the adaptive immune response. Cyclosporine mechanism of action is well described in the published literature and the myriad of benefits in all four stages lend a broad-based immunomodulatory function particularly suitable for addressing DED. Furthermore, cyclosporine has unique goblet cell density improvement capabilities as well as anti-apoptotic properties. Topical formulations of cyclosporine are centered around addressing the highly lipophilic nature of the molecule. The poor aqueous solubility of cyclosporine traditionally presented technical challenges in drug delivery to the ocular surface. Newer formulations such as cationic emulsions and nanomicellar aqueous solutions address formulation, tissue concentration, and drug delivery challenges.

Expression levels of CXCR4 and CXCL12 in patients with rheumatoid arthritis and its correlation with disease activity

The present study aimed to investigate the expression levels of C-X-C motif chemokine receptor 4 (CXCR4) and CXC ligand 12 (CXCL12) in patients with rheumatoid arthritis (RA) and the correlation with disease activity. In total, 60 patients with RA were selected as the study group, comprising of 28 patients in active-stage and 32 patients in remission-stage. In addition, 60 patients with osteoarthritis were selected as the control group. Western blotting and ELISA were used to detect the expression of CXCR4 and CXCL12, respectively. The Spearman's correlation test was used to analyze correlations between CXCR4 and CXCL12, and erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), disease activity score 28 (DAS28) scores and rheumatoid factor (RF). The present results suggested that CXCR4 and CXCL12 expression levels in the serum and joint synovial fluid of the study group were significantly higher compared with the control group (P<0.05). Moreover, CXCR4 and CXCL12 expression levels in the RA-active group were higher compared with the remission (P<0.05) and control groups (P<0.01). The Pearson test results suggested that the expression levels of CXCR4 and CXCL12 in the serum and joint synovial fluid of patients with RA had a positive correlation with the ESR, CRP, RF and DAS28 scores (P<0.05). CXCL12 and CXCR4 were highly expressed in the serum and joint synovial fluid of patients with RA, and these expression levels were positively correlated with ESR, CRP, RF and DAS28 scores. Therefore, these clinical parameters may be used as indicators to evaluate the disease activity of patients with RA.

Novel Analgesics with Peripheral Targets

A limited number of peripheral targets generate pain. Inflammatory mediators can sensitize these. The review addresses targets acting exclusively or predominantly on sensory neurons, mediators involved in inflammation targeting sensory neurons, and mediators involved in a more general inflammatory process, of which an analgesic effect secondary to an anti-inflammatory effect can be expected. Different approaches to address these systems are discussed, including scavenging proinflammatory mediators, applying anti-inflammatory mediators, and inhibiting proinflammatory or facilitating anti-inflammatory receptors. New approaches are contrasted to established ones; the current stage of progress is mentioned, in particular considering whether there is data from a molecular and cellular level, from animals, or from human trials, including an early stage after a market release. An overview of publication activity is presented, considering a IuPhar/BPS-curated list of targets with restriction to pain-related publications, which was also used to identify topics.

[HMGB1 as a target for prevention of chemotherapy-induced peripheral neuropathy]

Chemotherapy-induced peripheral neuropathy (CIPN) considerably impairs cancer patients' QOL, and may lead to discontinuation of drug treatment of cancer. Currently, there is no effective strategy against CIPN. Therefore, it is an urgent issue to develop clinically available drugs that prevent or treat CIPN. We have shown that high mobility group box 1 (HMGB1), a damage-associated molecular pattern (DAMP) molecule, plays an essential role in the development of CIPN. Most interestingly, thrombomodulin α, approved as a medicine for treatment of disseminated intravascular coagulation (DIC) in Japan, causes thrombin-dependent degradation of extracellular HMGB1 that is released in response to chemotherapeutics, and prevents CIPN. Thus, we expect that targeting HMGB1 or its receptors would lead to prevention of CIPN in cancer patients in near future.

MiR-187-3p mimic alleviates ischemia-reperfusion-induced pain hypersensitivity through inhibiting spinal P2X7R and subsequent mature IL-1β release in mice

BACKGROUND

Ischemia-reperfusion (IR)-induced pain hypersensitivity shares features of neuroinflammation and neuropathic pain, accompanied by overproduction of interleukin (IL)-1β. Multiple microRNAs (miRs) are dysregulated during IR; among these miRs, miR-187-3p was recently reported to drive IL-1β release in retinal disease by activating members of the purinergic receptor family. However, the roles of miR-187-3p in the spinal cord are unclear. Thus, we investigated whether miR-187-3p is involved in the pathogenesis of IR-induced pain hypersensitivity by regulating the P2X7R signal and subsequent IL-1β release.

METHODS

A mouse model was established by 5-min occlusion of the aortic arch. Pain hypersensitivity was assessed by the paw withdrawal threshold (PWT) and paw withdrawal latency (PWL). MiR-187-3p, P2X7R, cleaved caspase-1 and mature IL-1β expression levels were measured by RT-PCR and Western blotting. The in vivo roles of miR-187-3p, P2X7R and IL-1β were explored by intrathecal treatment with synthetic miRs, selective agonists and antagonists in separate experiments. Double immunofluorescence staining was performed to delineate the cellular distribution of P2X7R and IL-1β.

RESULTS

IR-induced progressively decreased PWT and PWL values were closely related to decreases in miR-187-3p and increases in P2X7R expression levels over time. The functional miR-187-3p/P2X7R pair was preliminarily predicted by a bioinformatic database and confirmed in vivo by quantitative analysis, as mimic-187 greatly increased miR-187-3p but decreased P2X7R expression levels, whereas inhibitor-187 reversed these changes. In contrast, downregulating P2X7R by mimic-187 or A-438079 treatment comparably increased PWT and PWL values in IR-injured mice, while upregulating P2X7R by inhibitor-187 or BzATP treatment decreased PWT and PWL values in sham-operated mice. Moreover, P2X7R and IL-1β immunoreactivities in each group were changed in the same patterns. This finding was further supported by results showing that downregulating IL-1β by A-438079 and IL-1β-neutralizing antibody similarly decreased P2X7R, cleaved caspase-1 and mature IL-1β expression levels, whereas BzATP treatment increased these levels. Expectedly, mimic-187 treatment preserved PWT and PWL values, with decreased cleaved caspase-1 and mature IL-1β expression levels, whereas inhibitor-187 reversed these effects.

CONCLUSIONS

The spinal miR-187-3p/P2X7R pair functioned in a mouse IR model. Increasing miR-187-3p protected against pain hypersensitivity and mature IL-1β overproduction, partially through inhibiting P2X7R activation.

CXCL12/CXCR4 signaling contributes to neuropathic pain via central sensitization mechanisms in a rat spinal nerve ligation model

Background

Previous studies have demonstrated that the CXCL12/CXCR4 signaling axis is involved in the regulation of neuropathic pain (NP). Here, we performed experiments to test whether the CXCL12/CXCR4 signaling pathway contributes to the pathogenesis of neuropathic pain after spinal nerve ligation (SNL) via central sensitization mechanisms.

Methods

Neuropathic pain was induced and assessed in a SNL rat model. The expression and distribution of CXCL12 or CXCR4 were examined by immunofluorescence staining and western blot. The effects of CXCL12 rat peptide, CXCL12 neutralizing antibody, CXCR4 antagonist, and astrocyte metabolic inhibitor on pain hypersensitivity were explored by behavioral tests in naive or SNL rats. We measured the expression level of c‐Fos and CGRP to evaluate the sensitization of neurons by RT‐PCR. The activation of astrocyte and microglia was analyzed by measuring the level of GFAP and iba‐1. The mRNA levels of the pro‐inflammatory cytokines such as TNF‐α, IL‐1β, and IL‐6 and Connexin 30, Connexin 43, EAAT 1, EAAT 2 were also detected by RT‐PCR.

Results

First, we found that the expression of CXCL12 and CXCR4 was upregulated after SNL. CXCL12 was mainly expressed in the neurons while CXCR4 was expressed both in astrocytes and neurons in the spinal dorsal horn after SNL. Moreover, intrathecal administration of rat peptide, CXCL12, induced hypersensitivity in naive rats, which was partly reversed by fluorocitrate. In addition, the CXCL12 rat peptide increased mRNA levels of c‐Fos, GFAP, and iba‐1. A single intrathecal injection of CXCL12 neutralizing antibody transiently reversed neuropathic pain in the SNL rat model. Consecutive use of CXCL12 neutralizing antibody led to significant delay in the induction of neuropathic pain, and reduced the expression of GFAP and iba‐1 in the spinal dorsal horn. Finally, repeated intrathecal administration of the CXCR4 antagonist, AMD3100, significantly suppressed the initiation and duration of neuropathic pain. The mRNA levels of c‐Fos, CGRP, GFAP, iba‐1, and pro‐inflammatory cytokines, also including Connexin 30 and Connexin 43 were decreased after injection of AMD3100, while EAAT 1 and EAAT 2 mRNAs were increased.

Conclusion

We demonstrate that the CXCL12/CXCR4 signaling pathway contributes to the development and maintenance of neuropathic pain via central sensitization mechanisms. Importantly, intervening with CXCL12/CXCR4 presents an effective therapeutic approach to treat the neuropathic pain.

Activation of GABAB Receptor Suppresses Diabetic Neuropathic Pain through Toll-Like Receptor 4 Signaling Pathway in the Spinal Dorsal Horn

Diabetic neuropathic pain (DNP) is a prevalent complication in diabetes patients. Neuronal inflammation and activation of Toll-like receptor 4 (TLR4) are involved in the occurrence of DNP. However, the underlying mechanisms remain unclear. Downregulation of gamma-aminobutyric acid B (GABA_B) receptor contributes to the DNP. GABA_B receptor interacts with NF-κB, a downstream signaling factor of TLR4, in a neuropathic pain induced by chemotherapy. In this study, we determined the role of TLR4/Myd88/NF-κB signaling pathways coupled to GABA_B receptors in the generation of DNP. Intrathecal injection of baclofen (GABA_B receptor agonist), LPS-RS ultrapure (TLR4 antagonist), MIP (MyD88 antagonist), or SN50 (NF-κB inhibitor) significantly increased paw withdrawal threshold (PWT) and paw withdrawal thermal latency (PWTL) in DNP rats, while intrathecal injection of saclofen (GABA_B receptor blocker) decreased PWT and PWTL in DNP rats. The expression of TLR4, Myd88, NF-κBp65, and their downstream components IL-1 and TNF-α was significantly higher in the spinal cord tissue in DNP rats compared to control rats. Following inhibition of TLR4, Myd88, and NF-κB, the expression of IL-1 and TNF-α decreased. Activation of GABA_B receptors downregulated the expression of TLR4, Myd88, NF-κBp65, IL-1, and TNF-α. Blockade of GABA_B receptors significantly upregulated expression of TLR4, Myd88, NF-κBp65, IL-1, and TNF-α. These data suggest that activation of the TLR4/Myd88/NF-κB signaling pathway is involved in the occurrence of DNP in rats. Activation of GABA_B receptor in the spinal cord may suppress the TLR4/Myd88/NF-κB signaling pathway and alleviate the DNP.

Low back pain and disc degeneration are decreased following chronic toll-like receptor 4 inhibition in a mouse model

OBJECTIVE

Intervertebral disc degeneration is a leading cause of chronic low back pain (LBP) but current treatment is limited. Toll-like receptors (TLRs) on disc cells are activated by endogenous extracellular matrix (ECM) fragments and modulate degeneration in vitro. This study investigated whether inhibiting TLR4 slows disc degeneration and reduces behavioral signs of LBP in vivo.

DESIGN

7-9-month old wild-type and secreted protein acidic and rich in cysteine (SPARC)-null (a model of disc degeneration and LBP) male mice were treated with TAK-242 (TLR4 inhibitor) once, and following a 10-day washout, mice were treated 3 times/week for 8 weeks. Behavioral signs of axial discomfort and radiating leg pain were assessed weekly with the grip force assay and acetone test, respectively. Following treatment, pain-related spinal cord changes were evaluated and lumbar discs were excised and cultured. Cytokine secretion from discs was evaluated with protein arrays.

RESULTS

SPARC-null mice displayed elevated signs of axial and radiating pain at baseline compared to wild-type. Chronic, but not acute, TLR4 inhibition reduced behavioral signs of pain compared to vehicle. SPARC-null mice have increased calcitonin gene-related peptide (CGRP)- and glial fibrillary acidic protein (GFAP)-immunoreactivity (astrocyte marker) in the dorsal horn compared to wild-type, which is reduced by chronic TLR4 inhibition. Ex vivo degenerating discs from SPARC-null mice secrete increased levels of many pro-inflammatory cytokines, which chronic TLR4 inhibition reduced.

CONCLUSION

Chronic TLR4 inhibition decreased behavioral signs of LBP, pain-related neuroplasticity and disc inflammation in SPARC-null mice. TAK-242 inhibits TLR4 activation within discs, as evidenced by decreases in cytokine release. Therefore, TLRs are potential therapeutic targets to slow disc degeneration and reduce pain.

Effect of Perioperative Opioids on Cancer-Relevant Circulating Parameters: Mu Opioid Receptor and Toll-Like Receptor 4 Activation Potential, and Proteolytic Profile

Purpose: The purpose of this study is to investigate the potential interplay between opioid analgesia and tumor metastasis through modulation of μ-opioid receptor (MOR), Toll-like receptor 4 (TLR4) activation, and matrix degradation potential.Experimental Design: Plasma samples were collected from 60 patients undergoing elective lower limb joint replacement preoperatively and at 3, 6, and 24 hours after surgery; pain scores were documented at the same time points. Opioid administration was recorded and converted into morphine IV equivalents. Plasma samples were also collected from 10 healthy volunteers. Alphascreen cyclic AMP assay and MOR-overexpressing cells were employed to quantify MOR activation. HEK-Blue hTLR4 were utilized to measure TLR4 activation. Circulating matrix metalloprotease and tissue inhibitor of matrix protease activities were assessed by gelatin zymography and reverse zymography, respectively.Results: Postoperative plasma samples displayed the ability to activate MOR and to inhibit lipopolysaccharide (LPS)-induced TLR4 activation. Linear mixed model analysis revealed that MOR activation had a significant effect on inhibition of LPS-induced TLR4 activation. Furthermore, TLR4 had a significant effect to explain pain scores. Postoperative samples also displayed altered circulating matrix-degrading enzymes activity potential, but this was correlated neither to opioid administration nor to MOR activation potential.Conclusions: Our results show for the first time that (i) opioids administered to surgery patients result in modulation of ligand-induced TLR4 activation and (ii) postoperative pain is associated with increased circulating TLR4 activation potential. Our study further promotes the use of MOR activation potential rather than opioid intake in clinical studies measuring opioid exposure at a given time point. Clin Cancer Res; 24(10); 2319-27. ©2018 AACR.

miRNA-23a/CXCR4 regulates neuropathic pain via directly targeting TXNIP/NLRP3 inflammasome axis

BACKGROUND

Chemokine CXC receptor 4 (CXCR4) in spinal glial cells has been implicated in neuropathic pain. However, the regulatory cascades of CXCR4 in neuropathic pain remain elusive. Here, we investigated the functional regulatory role of miRNAs in the pain process and its interplay with CXCR4 and its downstream signaling.

METHODS

miRNAs and CXCR4 and its downstream signaling molecules were measured in the spinal cords of mice with sciatic nerve injury via partial sciatic nerve ligation (pSNL). Immunoblotting, immunofluorescence, immunoprecipitation, and mammal two-hybrid and behavioral tests were used to explore the downstream CXCR4-dependent signaling pathway.

RESULTS

CXCR4 expression increased in spinal glial cells of mice with pSNL-induced neuropathic pain. Blocking CXCR4 alleviated the pain behavior; contrarily, overexpressing CXCR4 induced pain hypersensitivity. MicroRNA-23a-3p (miR-23a) directly bounds to 3' UTR of CXCR4 mRNA. pSNL-induced neuropathic pain significantly reduced mRNA expression of miR-23a. Overexpression of miR-23a by intrathecal injection of miR-23a mimics or lentivirus reduced spinal CXCR4 and prevented pSNL-induced neuropathic pain. In contrast, knockdown of miR-23a by intrathecal injection of miR-23a inhibitor or lentivirus induced pain-like behavior, which was reduced by CXCR4 inhibition. Additionally, miR-23a knockdown or CXCR4 overexpression in naïve mice could increase the thioredoxin-interacting protein (TXNIP), which was associated with induction of NOD-like receptor protein 3 (NLRP3) inflammasome. Indeed, CXCR4 and TXNIP were co-expressed. The mammal two-hybrid assay revealed the direct interaction between CXCR4 and TXNIP, which was increased in the spinal cord of pSNL mice. In particular, inhibition of TXNIP reversed pain behavior elicited by pSNL, miR-23a knockdown, or CXCR4 overexpression. Moreover, miR-23a overexpression or CXCR4 knockdown inhibited the increase of TXNIP and NLRP3 inflammasome in pSNL mice.

CONCLUSIONS

miR-23a, by directly targeting CXCR4, regulates neuropathic pain via TXNIP/NLRP3 inflammasome axis in spinal glial cells. Epigenetic interventions against miR-23a, CXCR4, or TXNIP may potentially serve as novel therapeutic avenues in treating peripheral nerve injury-induced nociceptive hypersensitivity.

Upregulation of Spinal Voltage-Dependent Anion Channel 1 Contributes to Bone Cancer Pain Hypersensitivity in Rats

Voltage-dependent anion channel 1 (VDAC1) is thought to contribute to the progression of tumor development. However, whether VDAC1 contributes to bone cancer pain remains unknown. In this study, we found that the expression of VDAC1 was upregulated in the L2-5 segments of the spinal dorsal horn at 2 and 3 weeks after injection of tumor cells into the tibial cavity. Intrathecal injection of a VDAC1 inhibitor significantly reversed the pain hypersensitivity and reduced the over-expression of Toll-like receptor 4 (TLR4). Intrathecal injection of minocycline, an inhibitor of microglia, also attenuated the pain hypersensitivity of rat models of bone cancer pain. These results suggest that VDAC1 plays a significant role in the development of complicated cancer pain, possibly by regulating the expression of TLR4.

SDF1-CXCR4 Signaling Maintains Central Post-Stroke Pain through Mediation of Glial-Neuronal Interactions

Central post-stroke pain (CPSP) is an intractable central neuropathic pain that has been poorly studied mechanistically. Here we showed that stromal cell-derived factor 1 (SDF1 or CXCL12), a member of the CXC chemokine family, and its receptor CXCR4 played a key role in the development and maintenance of thalamic hemorrhagic CPSP through hypoxia inducible factor 1α (HIF-1α) mediated microglial-astrocytic-neuronal interactions. First, both intra-thalamic collagenase (ITC) and SDF1 injections could induce CPSP that was blockable and reversible by intra-thalamic administration of both AMD3100 (a selective CXCR4 antagonist) and inhibitors of microglial or astrocytic activation. Second, long-term increased-expression of SDF1 and CXCR4 that was accompanied by activations of both microglia and astrocytes following ITC could be blocked by both AMD-3100 and YC-1, a selective inhibitor of HIF-1α. AMD-3100 could also inhibit release of proinflammatory mediators (TNFα, IL1β and IL-6). Increased-expression of HIF-1α, SDF1, CXCR4, Iba1 and GFAP proteins could be induced by both ITC and intra-thalamic CoCl₂, an inducer of HIF-1α that was blockable by both HIF-1α inhibition and CXCR4 antagonism. Finally, inhibition of HIF-1α was only effective in prevention, but not in treatment of ITC-induced CPSP. Taken together, the present study demonstrated that in the initial process of thalamic hemorrhagic state HIF-1α up-regulated SDF1-CXCR4 signaling, while in the late process SDF1-CXCR4 signaling-mediated positive feedback plays more important role in glial-glial and glial-neuronal interactions and might be a novel promising molecular target for treatment of CPSP in clinic.