MicroRNA-Based Biomarkers in Pain

Innovations in acute and chronic pain biomarkers: enhancing diagnosis and personalized therapy

Pain affects millions worldwide, posing significant challenges in diagnosis and treatment. Despite advances in understanding pain mechanisms, there remains a critical need for validated biomarkers to enhance diagnosis, prognostication, and personalized therapy. This review synthesizes recent advancements in identifying and validating acute and chronic pain biomarkers, including imaging, molecular, sensory, and neurophysiological approaches. We emphasize the emergence of composite, multimodal strategies that integrate psychosocial factors to improve the precision and applicability of biomarkers in chronic pain management. Neuroimaging techniques like MRI and positron emission tomography provide insights into structural and functional abnormalities related to pain, while electrophysiological methods like electroencepholography and magnetoencepholography assess dysfunctional processing in the pain neuroaxis. Molecular biomarkers, including cytokines, proteomics, and metabolites, offer diagnostic and prognostic potential, though extensive validation is needed. Integrating these biomarkers with psychosocial factors into clinical practice can revolutionize pain management by enabling personalized treatment strategies, improving patient outcomes, and potentially reducing healthcare costs. Future directions include the development of composite biomarker signatures, advances in artificial intelligence, and biomarker signature integration into clinical decision support systems. Rigorous validation and standardization efforts are also necessary to ensure these biomarkers are clinically useful. Large-scale collaborative research will be vital to driving progress in this field and implementing these biomarkers in clinical practice. This comprehensive review highlights the potential of biomarkers to transform acute and chronic pain management, offering hope for improved diagnosis, treatment personalization, and patient outcomes.

Temporal therapy utilizing exosomes derived from M2 macrophages demonstrates enhanced efficacy in alleviating neuropathic pain in diabetic rats

Background

Diabetic pain patients have increased pain at night. Exosomes can relieve neuropathic pain. This study aimed to investigate the efficacy of exosome administration at different time points in relieving diabetic neuropathic pain (DNP) in rats.

Methods

M2 macrophages from bone marrow were induced in mice and exosomes were extracted. A diabetic rat model was induced using streptozotocin, with the mechanical withdrawal threshold (MWT) of the rats being measured at ≤ 80% of the basal value after 14 days, indicating successful construction of the DNP rat model. Exosomes were administered on three consecutive days at ZT0 (zeitgeber time) and ZT12. Parameters including blood glucose levels, body weight, MWT, and thermal withdrawal latency (TWL) were assessed in the rats. The lumbar spinal cord of rats was examined on days 21 and 28 to measure inflammatory factors and observe the expression of M1 and M2 microglia. Furthermore, microglia were exposed to lipopolysaccharide (LPS) and LPS + exosomes in a controlled in vitro setting to assess alterations in microglia phenotype involving the NF-kB p65 and IKBα inflammatory signaling pathways.

Results

The findings revealed that administration of exosomes during the rat resting period at ZT12 resulted in increased MWT and TWL, as well as a shift in microglia polarization towards the M2 phenotype. In vitro analysis indicated that exosomes influenced microglia polarization and suppressed the phosphorylation of NF-kB p65 and IKBα.

Conclusions

Temporal therapy with exosomes effectively reduces pain in DNP rats by polarizing microglia and affecting NF-kB p65 and IKBα signaling pathways.

Neuron-glia crosstalk and inflammatory mediators in migraine pathophysiology

Migraine is a complex neurological disorder with neuroinflammation playing a crucial role in its pathogenesis. This review provides an overview of the neuroinflammation mechanisms in migraine, focusing on both cellular and molecular aspects. At the cellular level, we examine the role of glial cells, including astrocytes, microglia, oligodendrocytes in the central nervous system, and Schwann cells and satellite glial cells in the peripheral nervous system. On the molecular level, we explore the signaling pathways, including IL-1β, TNF-α, IL-6, and non-coding RNAs, that mediate cell interactions or independent actions. Some of the molecular signaling pathways mentioned, such as TNF-α and IL-1β, have been investigated as druggable targets. Recent advancements, such as [11C] PBR28-targeted imaging for visualizing astrocyte activation and single-cell sequencing for exploring cellular heterogeneity, represent breakthroughs in understanding the mechanisms of neuroinflammation in migraine. By considering factors for personalized treatments, estrogen and TRPM8 emerge as promising therapeutic targets regarding sexual dimorphism. These advancements may help bridge the gap between preclinical findings and clinical applications, ultimately leading to more precise and personalized options for migraine patients.

Therapeutic Implication of miRNAs as an Active Regulatory Player in the Management of Pain: A Review

Chronic pain is frequently associated with neuropathy, inflammation, or the malfunctioning of nerves. Chronic pain is associated with a significant burden of morbidity due to opioid use, associated with addiction and tolerance, and disability. MicroRNAs (miRs) are emerging therapeutic targets to treat chronic pain through the regulation of genes associated with inflammation, neuronal excitability, survival, or de-differentiation. In this review, we discuss the possible involvement of miRs in pain-related molecular pathways. miRs are known to regulate high-conviction pain genes, supporting their potential as therapeutic targets.

The role of micro-RNAs in neuropathic pain-a scoping review

Neuropathic pain can be caused by a lesion or disease of the somatosensory system characterised by pathological neuro-immune alterations. At a molecular level, microRNAs (miRNAs) act as regulators of gene expression orchestrating both immune and neuronal processes. Thus, miRNAs may act as essential modulators of processes for the establishment and maintenance of neuropathic pain. The objective/aims of this scoping review was to explore and chart the literature to identify miRNAs that are dysregulated in neuropathic pain. The following databases were searched from inception to March 2023: PubMed, EBSCO, CINAHL, Cochrane Library, and SCOPUS. Two independent reviewers screened, extracted data, and independently assessed the risk of bias in included studies. The JBI critical appraisal checklist was used for critical appraisal. A narrative synthesis was used to summarise the evidence. Seven studies (total of 384 participants) that met our eligibility criteria were included in this scoping review. Our review has identified different miRNAs that are commonly involved in the chronic neuropathic pain conditions including miR-132, miR-101, and miR-199a. Our review findings further suggest that expression of miRNAs to be significantly associated with increased diabetic disease duration, HbA1C levels, and fibrinogen levels. Our review findings suggest that there is clear association between miRNA expression and chronic neuropathic pain conditions. Therefore, increasing the specificity by selecting a candidate miRNA and identifying its target mRNA is an area of future research.

Concise review: Current understanding of extracellular vesicles to treat neuropathic pain

Extracellular vesicles (EVs) including exosomes are vesicular vesicles with phospholipid bilayer implicated in many cellular interactions and have the ability to transfer multiple types of cargo to cells. It has been found that EVs can package various molecules including proteins and nucleic acids (DNA, mRNA, and noncoding RNA). The discovery of EVs as carriers of proteins and various forms of RNA, such as microRNAs (miRNA) and long noncoding RNAs (lncRNA), has raised great interest in the field of drug delivery. Despite the underlying mechanisms of neuropathic pain being unclear, it has been shown that uncontrolled glial cell activation and the neuroinflammation response to noxious stimulation are important in the emergence and maintenance of neuropathic pain. Many studies have demonstrated a role for noncoding RNAs in the pathogenesis of neuropathic pain and EVs may offer possibilities as carriers of noncoding RNAs for potential in neuropathic pain treatment. In this article, the origins and clinical application of EVs and the mechanism of neuropathic pain development are briefly introduced. Furthermore, we demonstrate the therapeutic roles of EVs in neuropathic pain and that this involve vesicular regulation of glial cell activation and neuroinflammation.

Toward Composite Pain Biomarkers of Neuropathic Pain-Focus on Peripheral Neuropathic Pain

Chronic pain affects ~10-20% of the U.S. population with an estimated annual cost of $600 billion, the most significant economic cost of any disease to-date. Neuropathic pain is a type of chronic pain that is particularly difficult to manage and leads to significant disability and poor quality of life. Pain biomarkers offer the possibility to develop objective pain-related indicators that may help diagnose, treat, and improve the understanding of neuropathic pain pathophysiology. We review neuropathic pain mechanisms related to opiates, inflammation, and endocannabinoids with the objective of identifying composite biomarkers of neuropathic pain. In the literature, pain biomarkers typically are divided into physiological non-imaging pain biomarkers and brain imaging pain biomarkers. We review both types of biomarker types with the goal of identifying composite pain biomarkers that may improve recognition and treatment of neuropathic pain.

P2X7 receptor mediated release of microglial prostanoids and miRNAs correlates with reversal of neuropathic hypersensitivity in rats

BACKGROUND

P2X7 receptor antagonists have potential for treating various CNS diseases, including neuropathic pain, although none have been approved for clinical use. Reasons may include insufficient understanding of P2X7 receptor signaling in pain and the lack of a corresponding preclinical mechanistic biomarker.

METHODS

Lu AF27139 is a highly selective and potent small molecule antagonist at rat, mouse, and human forms of the P2X7 receptor, with excellent pharmacokinetic and CNS permeability properties. In the current experiments, we probed the utility of previously characterized and novel signaling cascades exposed to Lu AF27139 using cultured microglia combined with release assays. Subsequently, we assessed the biomarker potential of identified candidate molecules in the rat chronic constriction injury (CCI) model of neuropathic pain; study design limitations precluded their assessment in spared nerve injury (SNI) rats.

RESULTS

Lu AF27139 blocked several pain-relevant pathways downstream of P2X7 receptors in-vitro. At brain and spinal cord receptor occupancy levels capable of functionally blocking P2X7 receptors, it diminished neuropathic hypersensitivity in SNI rats, and less potently in CCI rats. Although tissue levels of numerous molecules previously linked to neuropathic pain and P2X7 receptor function (e.g. IL-6, IL-1β, cathepsin-S, 2-AG) were unaffected by CCI, Lu AF27139-mediated regulation of spinal PGE2 and miRNA (e.g. rno-miR-93-5p) levels increased by CCI aligned with its ability to diminish neuropathic hypersensitivity.

CONCLUSIONS

We have identified a pain-relevant P2X7 receptor-regulated mechanism in neuropathic rats that could hold promise as a translatable biomarker and by association enhance the clinical progression of P2X7 receptor antagonists in neuropathic pain.

MicroRNA-155-5p promotes neuroinflammation and central sensitization via inhibiting SIRT1 in a nitroglycerin-induced chronic migraine mouse model

Background

Previous studies have confirmed that the microglial activation and subsequent inflammatory responses in the trigeminal nucleus caudalis (TNC) are involved in the central sensitization of chronic migraine (CM). MicroRNA-155-5p has been shown to modulate the polarization of microglia and participate in inflammatory processes in a variety of neurological diseases. However, its role in CM remains unclear. The purpose of this study was to determine the precise role of miR-155-5p in CM.

Methods

A model of CM in C57BL/6 mice was established by recurrent intraperitoneal injection of nitroglycerin (NTG). Mechanical and thermal hyperalgesia were evaluated by Von Frey filaments and radiant heat. The expression of miR-155-5p was examined by qRT-PCR, and the mRNA and protein levels of silent information regulator 1(SIRT1) were measured by qRT-PCR, Western blotting (WB) and immunofluorescence (IF) analysis. The miR-155-5p antagomir, miR-155-5p agomir, SRT1720 (a SIRT1 activator) and EX527 (a SIRT1 inhibitor) were administered to confirm the effects of miR-155-5p and SIRT1 on neuroinflammation and the central sensitization of CM. ELISA, WB and IF assays were applied to evaluate the expression of TNF-α, myeloperoxidase (MPO), IL-10, p-ERK, p-CREB, calcitonin gene-related peptide (CGRP), c-Fos and microglial activation. The cellular localization of SIRT1 was illustrated by IF.

Results

After the NTG-induced mouse model of CM was established, the expression of miR-155-5p was increased. The level of SIRT1 was decreased, and partly colocalized with Iba1 in the TNC. The miR-155-5p antagomir and SRT1720 downregulated the expression of p-ERK, p-CREB, CGRP, and c-Fos, alleviating microglial activation and decreasing inflammatory substances (TNF-α, MPO). The administration of miR-155-5p agomir or EX527 exacerbated neuroinflammation and central sensitization. Importantly, the miR-155-5p agomir elevated CGRP and c-Fos expression and microglial activation, which could subsequently be alleviated by SRT1720.

Conclusions

These data demonstrate that upregulated miR-155-5p in the TNC participates in the central sensitization of CM. Inhibiting miR-155-5p alleviates neuroinflammation by activating SIRT1 in the TNC of CM mice.

Circulating miRNome of Trachemys scripta after elective gonadectomy under general anesthesia

Post-surgical management is an important issue in veterinary medicine, requiring biomarkers with high sensitivity and specificity for timely and effective treatment. Emerging evidence suggests that miRNAs are promising stress- and pain-related markers. The aims were to profile the circulating miRNA signature in plasma of turtles (Trachemysscripta) and point out potential candidate biomarkers to assess the status of the animal. The plasma of female turtles underwent surgical gonadectomy were collected 24 h pre-surgery, and 2.5 h and 36 h post-surgery. The expression of miRNAs was profiled by Next Generation Sequencing and the dysregulated miRNAs were validated using RT-qPCR. The diagnostic value of miRNAs was calculated by ROC curves. The results showed that 14 miRNAs were differentially expressed over time. RT-qPCR validation highlighted that 2-miR-499-3p and miR-203-5p-out of 8 miRNAs tested were effectively modulated. The Area Under the Curve (AUC) of miR-203-5p was fair (AUC 0.7934) in discriminating pre- and 36 h post-surgery samples and poor for other time points; the AUC of miR-499-3p was excellent (AUC 0.944) in discriminating pre-surgery and 2.5 h post-surgery samples, and fair in discriminating pre-surgery and 36 h post-surgery (AUC 0.7292) and 2.5 h and 36 h post-surgery (AUC 0.7569) samples. In conclusion, we demonstrated for the first time that miRNAs profile changes in plasma of turtles underwent surgical oophorectomy and identified miR-203-5p and miR-499-3p as potential candidate biomarkers to assess animals' status. Further studies are necessary to confirm their diagnostic value and to investigate functional and mechanistic networks to improve our understanding of the biological processes.

The Interplay between Chronic Pain, Opioids, and the Immune System

Chronic pain represents one of the most serious worldwide medical problems, in terms of both social and economic costs, often causing severe and intractable physical and psychological suffering. The lack of biological markers for pain, which could assist in forming clearer diagnoses and prognoses, makes chronic pain therapy particularly arduous and sometimes harmful. Opioids are used worldwide to treat chronic pain conditions, but there is still an ambiguous and inadequate understanding about their therapeutic use, mostly because of their dual effect in acutely reducing pain and inducing, at the same time, tolerance, dependence, and a risk for opioid use disorder. In addition, clinical studies suggest that opioid treatment can be associated with a high risk of immune suppression and the development of inflammatory events, worsening the chronic pain status itself. While opioid peptides and receptors are expressed in both central and peripheral nervous cells, immune cells, and tissues, the role of opioids and their receptors, when and why they are activated endogenously and what their exact role is in chronic pain pathways is still poorly understood. Thus, in this review we aim to highlight the interplay between pain and immune system, focusing on opioids and their receptors.

Discovery and validation of biomarkers to aid the development of safe and effective pain therapeutics: challenges and opportunities

Pain medication plays an important role in the treatment of acute and chronic pain conditions, but some drugs, opioids in particular, have been overprescribed or prescribed without adequate safeguards, leading to an alarming rise in medication-related overdose deaths. The NIH Helping to End Addiction Long-term (HEAL) Initiative is a trans-agency effort to provide scientific solutions to stem the opioid crisis. One component of the initiative is to support biomarker discovery and rigorous validation in collaboration with industry leaders to accelerate high-quality clinical research into neurotherapeutics and pain. The use of objective biomarkers and clinical trial end points throughout the drug discovery and development process is crucial to help define pathophysiological subsets of pain, evaluate target engagement of new drugs and predict the analgesic efficacy of new drugs. In 2018, the NIH-led Discovery and Validation of Biomarkers to Develop Non-Addictive Therapeutics for Pain workshop convened scientific leaders from academia, industry, government and patient advocacy groups to discuss progress, challenges, gaps and ideas to facilitate the development of biomarkers and end points for pain. The outcomes of this workshop are outlined in this Consensus Statement.

Tissue Specific Reference Genes for MicroRNA Expression Analysis in a Mouse Model of Peripheral Nerve Injury

MicroRNAs (miRNAs) have emerged as master switch regulators in many biological processes in health and disease, including neuropathy. miRNAs are commonly quantified by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), usually estimated as relative expression through reference genes normalization. Different non-coding RNAs (ncRNAs) are used for miRNA normalization; however, there is no study identifying the optimal reference genes in animal models for peripheral nerve injury. We evaluated the stability of eleven ncRNAs, commonly used for miRNA normalization, in dorsal root ganglia (DRG), dorsal horn of the spinal cord (dhSC), and medial prefrontal cortex (mPFC) in the mouse spared nerve injury (SNI) model. After RT-qPCR, the stability of each ncRNA was determined by using four different methods: BestKeeper, the comparative delta-Cq method, geNorm, and NormFinder. The candidates were rated according to their performance in each method and an overall ranking list was compiled. The most stable ncRNAs were: sno420, sno429, and sno202 in DRG; sno429, sno202, and U6 in dhSC; sno202, sno420, and sno142 in mPFC. We provide the first reference genes' evaluation for miRNA normalization in different neuronal tissues in an animal model of peripheral nerve injury. Our results underline the need for careful selection of reference genes for miRNA normalization in different tissues and experimental conditions. We further anticipate that our findings can be used in a broad range of nerve injury related studies, to ensure validity and promote reproducibility in miRNA quantification.

Adaptive mechanisms driving maladaptive pain: how chronic ongoing activity in primary nociceptors can enhance evolutionary fitness after severe injury

Chronic pain is considered maladaptive by clinicians because it provides no apparent protective or recuperative benefits. Similarly, evolutionary speculations have assumed that chronic pain represents maladaptive or evolutionarily neutral dysregulation of acute pain mechanisms. By contrast, the present hypothesis proposes that chronic pain can be driven by mechanisms that evolved to reduce increased vulnerability to attack from predators and aggressive conspecifics, which often target prey showing physical impairment after severe injury. Ongoing pain and anxiety persisting long after severe injury continue to enhance vigilance and behavioural caution, decreasing the heightened vulnerability to attack that results from motor impairment and disfigurement, thereby increasing survival and reproduction (fitness). This hypothesis is supported by evidence of animals surviving and reproducing after traumatic amputations, and by complex specializations that enable primary nociceptors to detect local and systemic signs of injury and inflammation, and to maintain low-frequency discharge that can promote ongoing pain indefinitely. Ongoing activity in nociceptors involves intricate electrophysiological and anatomical specializations, including inducible alterations in the expression of ion channels and receptors that produce persistent hyperexcitability and hypersensitivity to chemical signals of injury. Clinically maladaptive chronic pain may sometimes result from the recruitment of this powerful evolutionary adaptation to severe bodily injury. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Circulating Exosomal miR-20b-5p Is Elevated in Type 2 Diabetes and Could Impair Insulin Action in Human Skeletal Muscle

miRNAs are noncoding RNAs representing an important class of gene expression modulators. Extracellular circulating miRNAs are both candidate biomarkers for disease pathogenesis and mediators of cell-to-cell communication. We examined the miRNA expression profile of total serum and serum-derived exosome-enriched extracellular vesicles in people with normal glucose tolerance or type 2 diabetes. In contrast to total serum miRNA, which did not reveal any differences in miRNA expression, we identified differentially abundant miRNAs in patients with type 2 diabetes using miRNA expression profiles of exosome RNA (exoRNA). To validate the role of these differentially abundant miRNAs on glucose metabolism, we transfected miR-20b-5p, a highly abundant exoRNA in patients with type 2 diabetes, into primary human skeletal muscle cells. miR-20b-5p overexpression increased basal glycogen synthesis in human skeletal muscle cells. We identified AKTIP and STAT3 as miR-20b-5p targets. miR-20b-5p overexpression reduced AKTIP abundance and insulin-stimulated glycogen accumulation. In conclusion, exosome-derived extracellular miR-20b-5p is a circulating biomarker associated with type 2 diabetes that plays an intracellular role in modulating insulin-stimulated glucose metabolism via AKT signaling.

Regulation of proinflammatory genes by the circulating microRNA hsa-miR-939

Circulating microRNAs are beneficial biomarkers because of their stability and dysregulation in diseases. Here we sought to determine the role of miR-939, a miRNA downregulated in patients with complex regional pain syndrome (CRPS). Hsa-miR-939 is predicted to target several proinflammatory genes, including IL-6, VEGFA, TNFα, NFκB2, and nitric oxide synthase 2 (NOS2A). Binding of miR-939 to the 3' untranslated region of these genes was confirmed by reporter assay. Overexpression of miR-939 in vitro resulted in reduction of IL-6, NOS2A and NFκB2 mRNAs, IL-6, VEGFA, and NOS2 proteins and NFκB activation. We observed a significant decrease in the NOS substrate l-arginine in plasma from CRPS patients, suggesting reduced miR-939 levels may contribute to an increase in endogenous NOS2A levels and NO, and thereby to pain and inflammation. Pathway analysis showed that miR-939 represents a critical regulatory node in a network of inflammatory mediators. Collectively, our data suggest that miR-939 may regulate multiple proinflammatory genes and that downregulation of miR-939 in CRPS patients may increase expression of these genes, resulting in amplification of the inflammatory pain signal transduction cascade. Circulating miRNAs may function as crucial signaling nodes, and small changes in miRNA levels may influence target gene expression and thus disease.