Expression and Biological Functions of miRNAs in Chronic Pain: A Review on Human Studies

Pharmacogenetic landscape of pain management variants among Mediterranean populations

Background

Chronic pain is a major socioeconomic burden in the Mediterranean region. However, we noticed an under-representation of these populations in the pharmacogenetics of pain management studies. In this context, we aimed 1) to decipher the pharmacogenetic variant landscape among Mediterranean populations compared to worldwide populations in order to identify therapeutic biomarkers for personalized pain management and 2) to better understand the biological process of pain management through in silico investigation of pharmacogenes pathways.

Materials and Methods

We collected genes and variants implicated in pain response using the Prisma guidelines from literature and PharmGK database. Next, we extracted these genes from genotyping data of 829 individuals. Then, we determined the variant distribution among the studied populations using multivariate (MDS) and admixture analysis with R and STRUCTURE software. We conducted a Chi2 test to compare the interethnic frequencies of the identified variants. We used SNPinfo web server, miRdSNP database to identify miRNA-binding sites. In addition, we investigated the functions of the identified genes and variants using pathway enrichment analysis and annotation tools. Finally, we performed docking analysis to assess the impact of variations on drug interactions.

Results

We identified 63 variants implicated in pain management. MDS analysis revealed that Mediterranean populations are genetically similar to Mexican populations and divergent from other populations. STRUCTURE analysis showed that Mediterranean populations are mainly composed of European ancestry. We highlighted differences in the minor allele frequencies of three variants (rs633, rs4680, and rs165728) located in the COMT gene. Moreover, variant annotation revealed ten variants with potential miRNA-binding sites. Finally, protein structure and docking analysis revealed that two missense variants (rs4680 and rs6267) induced a decrease in COMT protein activity and affinity for dopamine.

Conclusion

Our findings revealed that Mediterranean populations diverge from other ethnic groups. Furthermore, we emphasize the importance of pain-related pathways and miRNAs to better implement these markers as predictors of analgesic responses in the Mediterranean region.

Risk factors and related miRNA phenotypes of chronic pain after thoracoscopic surgery in lung adenocarcinoma patients

Chronic postsurgical pain may have a substantial impact on patient's quality of life, and has highly heterogenous presentation amongst sufferers. We aimed to explore the risk factors relating to chronic pain and the related miRNA phenotypes in patients with lung adenocarcinoma after video-assisted thoracoscopic lobectomy to identify potential biomarkers. Our prospective study involved a total of 289 patients with early invasive adenocarcinoma undergoing thoracoscopic lobotomy and a follow-up period of 3 months after surgery. Blood was collected the day before surgery for miRNA detection and patient information including operation duration, duration of continuous drainage of the chest, leukocyte count before and after operation, and postoperative pain scores were recorded. Using clinical and biochemical information for each patient, the risk factors for chronic postsurgical pain and related miRNA phenotypes were screened. We found that chronic postsurgical pain was associated with higher body mass index; greater preoperative history of chronic pain; longer postoperative drainage tube retention duration; higher numerical rating scale scores one, two, and three days after surgery; and changes in miRNA expression, namely lower expression of miRNA 146a-3p and higher expression of miRNA 550a-3p and miRNA 3613-3p in peripheral blood (p < 0.05). Of these factors, patient body mass index, preoperative history of chronic pain, average numerical rating scale score after operation, and preoperative peripheral blood miRNA 550a-3P expression were independent risk factors for the development of chronic postsurgical pain. Identification of individual risk markers may aid the development and selection of appropriate preventive and control measures.

Epigenetic regulation in opioid induced hyperalgesia

About 25 million American adults experience pain daily and one of the most commonly prescribed drugs to treat pain are opioids. Prolonged opioid usage and dose escalations can cause a paradoxical response where patients experience enhanced pain sensitivity. This opioid induced hyperalgesia (OIH) is a major hurdle when treating pain in the clinic because its underlying mechanisms are still not fully understood. OIH is also commonly overlooked and lacks guidelines to prevent its onset. Research on pain disorders and opioid usage have recognized potential epigenetic drivers of disease including DNA methylation, histone modifications, miRNA regulation, but their involvement in OIH has not been well studied. This article discusses epigenetic changes that may contribute to pathogenesis, with an emphasis on miRNA alterations in OIH. There is a crucial gap in knowledge including how multiple epigenetic modulators contribute to OIH. Elucidating the epigenetic changes underlying OIH and the crosstalk among these mechanisms could lead to the development of novel targets for the prevention and treatment of this painful phenomena.

The over-expression of miRNA-206 in peripheral blood of patients with burning mouth syndrome and its relationship with anxiety and depression

BACKGROUND

Burning mouth syndrome (BMS) is characterised by persisting burning pain of the oral mucosa, and its etiopathogenesis remains poorly understood.

OBJECTIVES

Our study aimed to detect the expression of miRNA-206 in the blood and clarify the relationship among miRNA-206, pain, anxiety and depression of BMS patients.

METHODS

Thirty patients with BMS and 30 healthy individuals were enrolled in the experimental and control groups, respectively. Data on medical history and clinical oral examination for all participants were collected. Simultaneously, scores of Visual Analogous Scale (VAS), Self-rating Anxiety Scale (SAS) and Self-rating Depression Scale (SDS) were administered. The expression level of miRNA-206 in plasma were determined by RT-(q)PCR. Finally, the relationship of miRNA-206 expression with the VAS score, SAS score, and SDS score was analysed. Chi-square test and t-test were used for statistical analysis of the data, and p < .05 was considered statistically significant.

RESULTS

The majority of the patients with BMS identified the tongue as the main pain area, and showed dry mouth and poor sleep quality. The SAS and SDS scores of patients with BMS were higher than those of healthy controls (p < .05) and were positively correlated with VAS pain score. In addition, miRNA-206 expression was higher in patients with BMS than in healthy individuals (p < .05), and was positively correlated with the VAS and SDS scores (p < .05).

CONCLUSIONS

Patients with BMS suffer from pain and tend to be more anxious and depressed than healthy controls. miRNA-206 expression in the peripheral blood of patients with BMS is positively correlated with pain and depression, which may be involved in the pathogenesis of BMS.

The Association between Infant Colic and the Multi-Omic Composition of Human Milk

Infant colic is a common condition with unclear biologic underpinnings and limited treatment options. We hypothesized that complex molecular networks within human milk (i.e., microbes, micro-ribonucleic acids (miRNAs), cytokines) would contribute to colic risk, while controlling for medical, social, and nutritional variables. This hypothesis was tested in a cohort of 182 breastfed infants, assessed with a modified Infant Colic Scale at 1 month. RNA sequencing was used to interrogate microbial and miRNA features. Luminex assays were used to measure growth factors and cytokines. Milk from mothers of infants with colic (n = 28) displayed higher levels of Staphylococcus (adj. p = 0.038, d = 0.30), miR-224-3p (adj. p = 0.023, d = 0.33), miR-125b-5p (adj. p = 0.028, d = 0.29), let-7a-5p (adj. p = 0.028, d = 0.27), and miR-205-5p (adj. p = 0.029, d = 0.26) compared to milk from non-colic mother-infant dyads (n = 154). Colic symptom severity was directly associated with milk hepatocyte growth factor levels (R = 0.21, p = 0.025). A regression model involving let-7a-5p, miR-29a-3p, and Lactobacillus accurately modeled colic risk (X² = 16.7, p = 0.001). Molecular factors within human milk may impact colic risk, and provide support for a dysbiotic/inflammatory model of colic pathophysiology.

The temporal expression of circulating microRNAs after acute experimental pain in humans

BACKGROUND

MicroRNAs (miRNAs) can modulate several biological systems, including the pain system. This study aimed to evaluate the temporal expression of circulating miRNAs in the plasma of healthy volunteers as a marker for epigenetic changes before and after an acute, experimental, pain provocation by intramuscular hypertonic saline injection.

METHODS

Twenty volunteers were randomly allocated into two groups and received either hypertonic (pain) or isotonic (control) saline injection in the first dorsal interosseous muscle of their dominant hand. Pain intensity was continuously recorded for 20 minutes after injection on a VAS scale from 0 to 100 (0 indicates no pain and 100 the worst imaginable pain). Blood samples were taken at baseline, 30 minutes, 3 hours, and 24 hours post-injection, and plasma was separated. MiRNA extracts were used for RNA sequencing with the Illumina NextSeq platform. MiRNA transcripts were compared between the pain and the no-pain, control group at every time point. Significant differences were considered when folds were >2 and the False Discovery Rate was p < 0.05.

RESULTS

After 30 minutes, 4 miRNAs were significantly altered in the pain group compared to controls, which increased to 24 after 3 hours and to 42 after 24 hours from baseline (p < 0.0001). Two miRNAs were consistently upregulated throughout the experiment. Enrichment analysis showed significant miRNAs involved in brain perception of pain, brain signalling and response to stimuli.

CONCLUSIONS

This exploratory study is the first to report on the temporal expression of circulating miRNAs after an acute, human experimental muscle pain model.

SIGNIFICANCE

This exploratory study evaluated the temporal profile of circulating miRNAs in the plasma of healthy subjects after acute experimental pain. Several miRNAs were altered in subjects at the times of follow-up after the acute pain model when compared to controls. MiRNAs previously associated with pain processes were altered in the pain group. Our results, by showing the fast and prolonged modifications of miRNA elicited by the acute experimental pain model, add new perspectives to the topic of epigenetics and pain.

Analysis of clinical characteristics of centrally mediated abdominal pain syndrome, exploration of diagnostic markers and its relationship with the efficacy of duloxetine treatment

INTRODUCTION

Centrally mediated abdominal pain syndrome (CAPS) is characterized by severe abdominal pain. Diagnosis of CAPS is still an exclusionary diagnosis, there remain no effective diagnostic biomarkers so far. Duloxetine is the major pharmacotherapy of CAPS, while some CAPS patients do not respond to duloxetine treatment. However, there is a lack of molecular markers to predict the efficacy of duloxetine. In our pilot study, we have found differential expression profiles of serum miRNAs between CAPS patients and healthy controls. Our study aims to explore the clinical characteristics, specific miRNAs in serum as diagnostic biomarkers of CAPS and predictive biomarkers of the efficacy of duloxetine.

METHODS/DESIGN

In this prospective cohort study, we plan to enroll 430 participants including 215 CAPS patients and 215 healthy controls. The CAPS group takes duloxetine 30 mg per day as an initial dose. Patients will have 24-week medication period and follow up at week 0, 4, 12, 24 and 36. Blood samples will be obtained from patients at every visits and health controls at the initial visit and a series of questionnaires will be completed by the participants. The primary end points are: The differential expression of miRNAs between CAPS groups and healthy control groups at baseline. The changes in abdominal pain scores before and after duloxetine treatment in patients with CAPS and their relationship with the changes in miRNAs. The secondary end point is the changes in scores of depression, anxiety, sleep quality and quality of life before and after duloxetine treatment in patients with CAPS and their relationship with changes in miRNAs.

DISCUSSION

Findings of study will provide the reliable basis for diagnosis and the predictor of duloxetine efficacy of CAPS. Importantly, findings grant patients a chance to benefit from treatment.

Role of Epigenetic Mechanisms in Chronic Pain

Pain is an unpleasant but essential-to-life sensation, usually resulting from tissue damage. When pain persists long after the injury has resolved, it becomes pathological. The precise molecular and cellular mechanisms causing the transition from acute to chronic pain are not fully understood. A key aspect of pain chronicity is that several plasticity events happen along the neural pathways involved in pain. These long-lasting adaptive changes are enabled by alteration in the expression of relevant genes. Among the different modulators of gene transcription in adaptive processes in the nervous system, epigenetic mechanisms play a pivotal role. In this review, I will first outline the main classes of epigenetic mediators and then discuss their implications in chronic pain.