Sphingosine 1-phosphate receptor modulation attenuate mechanical allodynia in mouse model of chronic complex regional pain syndrome by suppressing pathogenic astrocyte activation

An overview of sphingosine-1-phosphate receptor 2: Structure, biological function, and small-molecule modulators

Over the past decade, there has been a notable increase in research on sphingosine-1-phosphate receptor 2 (S1PR2), which is a type of G-protein-coupled receptor. Upon activation by S1P or other ligands, S1PR2 initiates downstream signaling pathways such as phosphoinositide 3-kinase (PI3K), Mitogen-activated protein kinase (MAPK), Rho/Rho-associated coiled-coil containing kinases (ROCK), and others, contributing to the diverse biological functions of S1PR2 and playing a pivotal role in various physiological processes and disease progressions, such as multiple sclerosis, fibrosis, inflammation, and tumors. Due to the extensive biological functions of S1PR2, many S1PR2 modulators, including agonists and antagonists, have been developed and discovered by pharmaceutical companies (e.g., Novartis and Galapagos NV) and academic medicinal chemists for disease diagnosis and treatment. However, few reviews have been published that comprehensively overview the functions and regulators of S1PR2. Herein, we provide an in-depth review of the advances in the function of S1PR2 and its modulators. We first summarize the structure and biological function of S1PR2 and its pathological role in human diseases. We then focus on the discovery approach, design strategy, development process, and biomedical application of S1PR2 modulators. Additionally, we outline the major challenges and future directions in this field. Our comprehensive review will aid in the discovery and development of more effective and clinically applicable S1PR2 modulators.

Experience from a single-center study on multimodal medication therapy for patients with complex regional pain syndrome

BACKGROUND

Despite the application of various therapeutic methods, pain caused by complex regional pain syndrome (CRPS) is not sufficiently managed and often progresses to a chronic stage. For the systematic and effective treatment of CRPS, we developed an algorithm for multimodal medication therapy based on the established pathophysiology of CRPS to control CRPS-related pain.

OBJECTIVE

In this study, we present the outcomes of our novel algorithm for multimodal medication therapy for patients with CRPS, consisting of three major components: multimodal oral medication, intravenous ketamine, and intravenous lidocaine therapy.

METHODS

We retrospectively investigated patients with CRPS who received multimodal therapy. Pain severity scores were evaluated using a numerical rating scale at four time points (P1, pain at initial consultation; P2, pain after oral medication; P3, pain after ketamine treatment; and P4, pain after lidocaine treatment). The effect of the multimodal medication therapy algorithm on pain management was evaluated at each time point.

RESULTS

In patients with CRPS, multimodal oral medication, intravenous ketamine, and intravenous lidocaine therapies led to significantly improved pain control (p< 0.05). Additionally, the combination of these three therapies (through the multimodal medication therapy algorithm) resulted in significant pain relief in patients with CRPS (p< 0.05).

CONCLUSIONS

Our multimodal medication therapy algorithm effectively controlled pain in patients with CRPS. However, further prospective studies with large sample sizes and randomized controlled trials are needed for more accurate generalization.

Complex Regional Pain Syndrome: Evidence-Based Advances in Concepts and Treatments

PURPOSE OF REVIEW

This review presents the most current information about the epidemiology of complex regional pain syndrome (CRPS), classification and diagnostic criteria, childhood CRPS, subtypes, pathophysiology, conventional and less conventional treatments, and preventive strategies.

RECENT FINDINGS

CRPS is a painful disorder with multifactorial pathophysiology. The data describe sensitization of the central and peripheral nervous systems, inflammation, possible genetic factors, sympatho-afferent coupling, autoimmunity, and mental health factors as contributors to the syndrome. In addition to conventional subtypes (type I and type II), cluster analyses have uncovered other proposed subtypes. Prevalence of CRPS is approximately 1.2%, female gender is consistently associated with a higher risk of development, and substantial physical, emotional, and financial costs can result from the syndrome. Children with CRPS seem to benefit from multifaceted physical therapy leading to a high percentage of symptom-free patients. The best available evidence along with standard clinical practice supports pharmacological agents, physical and occupational therapy, sympathetic blocks for engaging physical restoration, steroids for acute CRPS, neuromodulation, ketamine, and intrathecal baclofen as therapeutic approaches. There are many emerging treatments that can be considered as a part of individualized, patient-centered care. Vitamin C may be preventive. CRPS can lead to progressively painful sensory and vascular changes, edema, limb weakness, and trophic disturbances, all of which substantially erode healthy living. Despite some progress in research, more comprehensive basic science investigation is needed to clarify the molecular mechanisms of the disease so that targeted treatments can be developed for better outcomes. Incorporating a variety of standard therapies with different modes of action may offer the most effective analgesia. Introducing less conventional approaches may also be helpful when traditional treatments fail to provide sufficient improvement.

Animal models of complex regional pain syndrome: A scoping review

BACKGROUND

complex regional pain syndrome (CRPS) leads to a debilitating chronic pain condition. The lack of cause, etiology, and treatment for CRPS has been widely explored in animal models.

OBJECTIVE

Provide a comprehensive framework of the animal models used for investigating CRPS.

ELIGIBILITY CRITERIA

Preclinical studies to induce the characteristics of CRPS, with a control group, in any language or publication date.

SOURCES OF EVIDENCE

The search was performed in the Medline (PubMed) and ScienceDirect databases.

RESULTS

93 studies are included. The main objective of the included studies was to understand the CRPS model. Rats, males and adults, exposed to ischemia/reperfusion of the paw or fracture of the tibia were the most common characteristics. Nociceptive evaluation using von Frey monofilaments was the most widely adopted in the studies.

CONCLUSIONS

For the best translational science between the animal models and individuals with CRPS, future studies should include more heterogeneous animals, and multiple assessment tools, in addition to improving the description and performance of measures that reduce the risk of bias.

DICAM in the Extracellular Vesicles from Astrocytes Attenuates Microglia Activation and Neuroinflammation

Cross-talk between astrocytes and microglia plays an important role in neuroinflammation and central sensitization, but the manner in which glial cells interact remains less well-understood. Herein, we investigated the role of dual immunoglobulin domain-containing cell adhesion molecules (DICAM) in the glial cell interaction during neuroinflammation. DICAM knockout (KO) mice revealed enhanced nociceptive behaviors and glial cell activation of the tibia fracture with a cast immobilization model of complex regional pain syndrome (CRPS). DICAM was selectively secreted in reactive astrocytes, mainly via extracellular vesicles (EVs), and contributed to the regulation of neuroinflammation through the M2 polarization of microglia, which is dependent on the suppression of p38 MAPK signaling. In conclusion, DICAM secreted from reactive astrocytes through EVs was involved in the suppression of microglia activation and subsequent attenuation of neuroinflammation during central sensitization.

Sphingosine-1 phosphate receptor 1 contributes to central sensitization in recurrent nitroglycerin-induced chronic migraine model

BACKGROUND

Central sensitization is an important pathophysiological mechanism of chronic migraine (CM), and microglia activation in trigeminocervical complex (TCC) contributes to the development of central sensitization. Emerging evidence implicates that blocking sphingosine-1-phosphate receptor 1 (S1PR1) can relieve the development of chronic pain and inhibit the activation of microglia. However, it is unclear whether S1PR1 is involved in the central sensitization of CM. Therefore, the purpose of this study is to explore the role of S1PR1 and its downstream signal transducers and activators of transcription 3 (STAT3) signaling pathway in the CM, mainly in inflammation.

METHODS

Chronic intermittent intraperitoneal injection of nitroglycerin (NTG) established a mouse model of CM. First, we observed the changes and subcellular localization of S1PR1 in the trigeminocervical complex (TCC). Then, W146, a S1PR1 antagonist; SEW2871, a S1PR1 agonist; AG490, a STAT3 inhibitor were applied by intraperitoneal injection to investigate the related molecular mechanism. The changes in the number of microglia and the expression of calcitonin gene-related peptide (CGRP) and c-fos in the TCC site were explored by immunofluorescence. In addition, we studied the effect of S1PR1 inhibitors on STAT3 in lipopolysaccharide-treated BV-2 microglia.

RESULTS

Our results showed that the expression of S1PR1 was increased after NTG injection and S1PR1 was colocalized with in neurons and glial cells in the TCC. The S1PR1 antagonist W146 alleviated NTG-induced hyperalgesia and suppressed the upregulation of CGRP, c-fos and pSTAT3 in the TCC. Importantly, blocking S1PR1 reduced activation of microglia. In addition, we found that inhibiting STAT3 signal also attenuated NTG-induced basal mechanical and thermal hyperalgesia.

CONCLUSIONS

Our results indicate that inhibiting S1PR1 signal could alleviate central sensitization and inhibit microglia activity caused by chronic NTG administration via STAT3 signal pathway, which provide a new clue for the clinical treatment of CM.

Astrocytes in rare neurological conditions: Morphological and functional considerations

Astrocytes are a population of central nervous system (CNS) cells with distinctive morphological and functional characteristics that differ within specific areas of the brain and are widely distributed throughout the CNS. There are mainly two types of astrocytes, protoplasmic and fibrous, which differ in morphologic appearance and location. Astrocytes are important cells of the CNS that not only provide structural support, but also modulate synaptic activity, regulate neuroinflammatory responses, maintain the blood-brain barrier, and supply energy to neurons. As a result, astrocytic disruption can lead to widespread detrimental effects and can contribute to the pathophysiology of several neurological conditions. The characteristics of astrocytes in more common neuropathologies such as Alzheimer's and Parkinson's disease have significantly been described and continue to be widely studied. However, there still exist numerous rare neurological conditions in which astrocytic involvement is unknown and needs to be explored. Accordingly, this review will summarize functional and morphological changes of astrocytes in various rare neurological conditions based on current knowledge thus far and highlight remaining neuropathologies where astrocytic involvement has yet to be investigated.

The effect of rTMS in the management of pain associated with CRPS

Background

Therapeutic management of pain in patients with complex regional pain syndrome (CRPS) is challenging. Repetitive transcranial magnetic stimulation (rTMS) has analgesic effects on several types of pain. However, its effect on CRPS has not been elucidated clearly. Therefore, we conducted a meta-analysis of the available clinical studies on rTMS treatment in patients with CRPS.

Materials and methods

A comprehensive literature search was conducted using the PubMed, EMBASE, Cochrane Library, and SCOPUS databases. We included studies published up to February 09, 2020, that fulfilled our inclusion and exclusion criteria. Data regarding measurement of pain using the visual analog scale before and after rTMS treatment were collected to perform the meta-analysis. The meta-analysis was performed using Comprehensive Meta-analysis Version 2.

Results

A total of three studies (one randomized controlled trial and two prospective observational studies) involving 41 patients were included in this meta-analysis. No significant reduction in pain was observed immediately after one rTMS treatment session or immediately after the entire schedule of rTMS treatment sessions (5 or 10 sessions; P > 0.05). However, pain significantly reduced 1 week after the entire schedule of rTMS sessions (P < 0.001).

Conclusion

rTMS appears to have a functional analgesic effect in patients with CRPS.

Effectiveness of Intravenous Immunoglobulin for Management of Neuropathic Pain: A Narrative Review

Administrations of intravenous immunoglobulin (IVIG), an immune-modulating blood-derived product, may be beneficial for managing neuropathic pain. Here, we review previous studies to investigate the effectiveness of IVIG in managing neuropathic pain due to various neurological disorders. The electronic databases PubMed, Scopus, Embase, and the Cochrane Library were searched for studies published up to February 2020. Two reviewers independently assessed the studies using strict inclusion criteria. Ten studies were included and qualitatively analyzed. The review included patients with pain due to complex regional pain syndrome (CRPS), diabetic polyneuropathy, and others, such as postherpetic neuralgia and trigeminal neuralgia. We found that IVIG may be one of the beneficial options for managing neuropathic pain from various neurological disorders. In the four articles reviewed, no major adverse effects were reported, and the trend was toward a positive pain-reducing effect in eight articles. However, to confirm the benefits of IVIG on reducing neuropathic pain, more high-quality studies are required.

The ceramide-S1P pathway as a druggable target to alleviate peripheral neuropathic pain

Introduction: Neuropathic pain disorders are diverse, and the currently available therapies are ineffective in the majority of cases. Therefore, there is a major need for gaining novel mechanistic insights and developing new treatment strategies for neuropathic pain. Areas covered: We performed an in-depth literature search on the molecular mechanisms and systemic importance of the ceramide-to-S1P rheostat regulating neuron function and neuroimmune interactions in the development of neuropathic pain. Expert opinion: The S1P receptor modulator FTY720 (fingolimod, Gilenya®), LPA receptor antagonists and several mechanistically related compounds in clinical development raise great expectations for treating neuropathic pain disorders. Research on S1P receptors, S1P receptor modulators or SPHK inhibitors with distinct selectivity, pharmacokinetics and safety must provide more mechanistic insight into whether they may qualify as useful treatment options for neuropathic pain disorders. The functional relevance of genetic variations within the ceramide-to-S1P rheostat should be explored for an enhanced understanding of neuropathic pain pathogenesis. The ceramide-to-S1P rheostat is emerging as a critically important regulator hub of neuroimmune interactions along the pain pathway, and improved mechanistic insight is required to develop more precise and effective drug treatment options for patients suffering from neuropathic pain disorders.

Molecular Effects of FDA-Approved Multiple Sclerosis Drugs on Glial Cells and Neurons of the Central Nervous System

Multiple sclerosis (MS) is characterized by peripheral and central inflammatory features, as well as demyelination and neurodegeneration. The available Food and Drug Administration (FDA)-approved drugs for MS have been designed to suppress the peripheral immune system. In addition, however, the effects of these drugs may be partially attributed to their influence on glial cells and neurons of the central nervous system (CNS). We here describe the molecular effects of the traditional and more recent FDA-approved MS drugs Fingolimod, Dimethyl Fumarate, Glatiramer Acetate, Interferon-β, Teriflunomide, Laquinimod, Natalizumab, Alemtuzumab and Ocrelizumab on microglia, astrocytes, neurons and oligodendrocytes. Furthermore, we point to a possible common molecular effect of these drugs, namely a key role for NFκB signaling, causing a switch from pro-inflammatory microglia and astrocytes to anti-inflammatory phenotypes of these CNS cell types that recently emerged as central players in MS pathogenesis. This notion argues for the need to further explore the molecular mechanisms underlying MS drug action.