Enrichment of Genomic Pathways Based on Differential DNA Methylation Associated With Chronic Postsurgical Pain and Anxiety in Children: A Prospective, Pilot Study

The role of cytokines in acute and chronic postsurgical pain after major musculoskeletal surgeries in a quaternary pediatric center

STUDY OBJECTIVE

To determine if baseline cytokines/chemokines and their changes over postoperative days 0-2 (POD0-2) predict acute and chronic postsurgical pain (CPSP) after major surgery.

DESIGN

Prospective, observational, longitudinal nested study.

SETTING

University-affiliated quaternary children's hospital.

PATIENTS

Subjects (≥8 years old) with idiopathic scoliosis undergoing spine fusion or pectus excavatum undergoing Nuss procedure.

MEASUREMENTS

Demographics, surgical, psychosocial measures, pain scores, and opioid use over POD0-2 were collected. Cytokine concentrations were analyzed in serial blood samples collected before and up to two weeks after surgery, using Luminex bead arrays. After data preparation, relationships between pre- and post-surgical cytokine concentrations with acute (% time in moderate-severe pain over POD0-2) and chronic (pain score > 3/10 beyond 3 months post-surgery) post-surgical pain were analyzed using univariable and multivariable regression analyses with adjustment for covariates and mixed effects models were used to associate longitudinal cytokine concentrations with pain outcomes.

MAIN RESULTS

Analyses included 3,164 repeated measures of 16 cytokines/chemokines from 112 subjects (median age 15.3, IQR 13.5-17.0, 54.5 % female, 59.8 % pectus). Acute postsurgical pain was associated with higher baseline concentrations of GM-CSF (β = 0.95, SE 0.31; p = 0.003), IL-1β (β = 0.84, SE 0.36; p = 0.02), IL-2 (β = 0.78, SE 0.34; p = 0.03), and IL-12 p70 (β = 0.88, SE 0.40; p = 0.03) and longitudinal postoperative elevations in GM-CSF (β = 1.38, SE 0.57; p = 0.03), IFNγ (β = 1.36, SE 0.6; p = 0.03), IL-1β (β = 1.25, SE 0.59; p = 0.03), IL-7 (β = 1.65, SE 0.7; p = 0.02), and IL-12 p70 (β = 1.17, SE 0.58; p = 0.04). In contrast, CPSP was associated with lower baseline concentration of IL-8 (β = -0.39, SE 0.17; p = 0.02), and the risk of developing CPSP was elevated in patients with lower longitudinal postoperative concentrations of IL-6 (β = -0.57, SE 0.26; p = 0.03), IL-8 (β = -0.68, SE 0.24; p = 0.006), and IL-13 (β = -0.48, SE 0.22; p = 0.03). Covariates female (vs. male) sex and surgery type (pectus surgery vs. spine) were associated with higher odds for CPSP in baseline adjusted cytokine-CPSP association models for IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, TNFα, and IL-8, IL-10, respectively.

CONCLUSION

We identified pro-inflammatory cytokine profiles associated with higher risk of acute postoperative pain. Interestingly, pleiotropic cytokine IL-6, chemokine IL-8 (which promotes neutrophil infiltration and monocyte differentiation), and monocyte-released anti-inflammatory cytokine IL-13, were associated with lower CPSP risk. Our results suggest heterogenous outcomes of cytokine/chemokine signaling that can both promote and protect against post-surgical pain. These may serve as predictive and prognostic biomarkers of pain outcomes following surgery.

A systematic review of the prevalence of chronic postsurgical pain in children

Two prior reviews highlight the scarcity and conflicting nature of available data on chronic postsurgical pain in children, reporting a wide prevalence range of 3.2% to 64% (at ≥3 months). This updated systematic review aimed to consolidate information on the prevalence of pediatric chronic postsurgical pain. A thorough literature search of full English-text publications from April 2014 to August 2021 was conducted using Ovid MEDLINE, PubMed, and Cochrane Database of Systematic Reviews, with search terms: postoperative pain, child, preschool, pediatrics, adolescent, chronic pain. Seventeen relevant studies were identified. Most assessed chronicity once greater than 3 months duration postoperatively (82%), were predominantly prospective (71%) and conducted in inpatient settings (88%). The surgeries examined included orthopedic (scoliosis and limb), urological, laparotomy, inguinal, and cardiothoracic procedures, involving numbers ranging from 36 to 750, totaling 3137 participants/2792 completers. The studies had wide variations in median age at surgery (6 days to 16 years), the percentage of female participants (unspecified or 12.5% to 90%), and follow-up duration (2.5 months to 9 years). Various pain, functional, psychosocial, and health-related quality of life outcomes were documented. Chronic postsurgical pain prevalence varied widely from 2% to 100%. Despite increased data, challenges persist due to heterogeneity in definitions, patient demographics, mixed versus single surgical populations, diverse perioperative analgesic interventions, follow-up durations and reported outcomes. Interpretation is further complicated by limited information on impact, long-term analgesia and healthcare utilization, and relatively small sample sizes, hindering the assessment of reported associations. In some cases, preoperative pain and deformity may not have been addressed by surgery and persisting pain postoperatively may then be inappropriately termed chronic postsurgical pain. Larger-scale, procedure-specific data to better assess current prevalence, impact, and whether modifiable factors link to negative long-term outcomes, would be more useful and allow targeted perioperative interventions for at-risk pediatric surgical patients.

Prevalence, pain trajectories, and presurgical predictors for chronic postsurgical pain in a pediatric sample in Spain with a 24-month follow-up

ABSTRACT

Pediatric chronic pain, particularly chronic postsurgical pain (CPSP), poses a significant public health challenge, impacting 20% of pediatric populations. While several presurgical predictors have been identified, there is a scarcity of data on long-term outcomes, especially beyond 1 to 2 years postsurgery. Previous research primarily focuses on North American children, creating gaps in understanding CPSP outcomes in diverse health systems, such as in Spain. This study, registered as NCT04735211, investigates CPSP in 159 children and adolescents (mean age = 12.4 years, 37.1% girls, retention rate = 65%) undergoing various surgeries in Spain. The objectives include examining CPSP prevalence (Numerical Rating Scale ≥ 4) at 3, 6, 12, and 24 months, exploring postsurgical pain trajectories through group-based trajectory modeling, and identifying potential presurgical predictors for CPSP (pain intensity, pain catastrophizing, pain anxiety, fear of pain, kinesiophobia, health-related quality of life, pain interference, and physical activity), using multiple logistic regressions. Results show a CPSP prevalence of 41% at 3 months, decreasing to 14% at 24 months. Presurgical factors including pain intensity (adjusted odds ratio [aOR] = 1.25, 95% confidence interval [CI] = 1.02-1.53), pain catastrophizing (aOR = 1.06, 95% CI = 1.00-1.13), and pain anxiety (aOR = 1.06, 95% CI = 1.02-1.11) were associated with CPSP at 3 months. Group-based trajectory modeling revealed 3 postsurgical pain trajectories: Low Pain with Rapid Recovery Group (30.2%), Moderate Pain with Recovery Group (53.5%), and High Pain with Slow Recovery Group (16.3%), with group differences in presurgical predictors, excluding physical activity. This study contributes valuable insights into CPSP, emphasizing the need for long-term follow-up. The findings could inform the implementation of preventive programs for CPSP into diverse health systems.

Whole-genome methylation profiling reveals regions associated with painful temporomandibular disorders and active recovery processes

ABSTRACT

Temporomandibular disorders (TMDs), collectively representing one of the most common chronic pain conditions, have a substantial genetic component, but genetic variation alone has not fully explained the heritability of TMD risk. Reasoning that the unexplained heritability may be because of DNA methylation, an epigenetic phenomenon, we measured genome-wide DNA methylation using the Illumina MethylationEPIC platform with blood samples from participants in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) study. Associations with chronic TMD used methylation data from 496 chronic painful TMD cases and 452 TMD-free controls. Changes in methylation between enrollment and a 6-month follow-up visit were determined for a separate sample of 62 people with recent-onset painful TMD. More than 750,000 individual CpG sites were examined for association with chronic painful TMD. Six differentially methylated regions were significantly ( P < 5 × 10 -8 ) associated with chronic painful TMD, including loci near genes involved in the regulation of inflammatory and neuronal response. A majority of loci were similarly differentially methylated in acute TMD consistent with observed transience or persistence of symptoms at follow-up. Functional characterization of the identified regions found relationships between methylation at these loci and nearby genetic variation contributing to chronic painful TMD and with gene expression of proximal genes. These findings reveal epigenetic contributions to chronic painful TMD through methylation of the genes FMOD , PM20D1 , ZNF718 , ZFP57 , and RNF39 , following the development of acute painful TMD. Epigenetic regulation of these genes likely contributes to the trajectory of transcriptional events in affected tissues leading to resolution or chronicity of pain.

The Role of Cytokines in Acute and Chronic Postsurgical Pain in Pediatric Patients after Major Musculoskeletal Surgeries

Study Objective

To determine if baseline cytokines and their changes over postoperative days 0-2 (POD0-2) predict acute and chronic postsurgical pain (CPSP) after major surgery.

Design

Prospective, observational, longitudinal nested study.

Setting

University-affiliated quaternary children's hospital.

Patients

Subjects (≥8 years old) with idiopathic scoliosis undergoing spine fusion or pectus excavatum undergoing Nuss procedure.

Measurements

Demographics, surgical, psychosocial measures, pain scores, and opioid use over POD0-2 were collected. Cytokine concentrations were analyzed in serial blood samples collected before and after (up to two weeks) surgery, using Luminex bead arrays. After data preparation, relationships between pre- and post-surgical cytokine concentrations with acute (% time in moderate-severe pain over POD0-2) and chronic (pain score>3/10 beyond 3 months post-surgery) pain were analyzed. After adjusting for covariates, univariate/multivariate regression analyses were conducted to associate baseline cytokine concentrations with postoperative pain, and mixed effects models were used to associate longitudinal cytokine concentrations with pain outcomes.

Main Results

Analyses included 3,164 measures of 16 cytokines from 112 subjects (median age 15.3, IQR 13.5-17.0, 54.5% female, 59.8% pectus). Acute postsurgical pain was associated with higher baseline concentrations of GM-CSF (β=0.95, SE 0.31; p=.003), IL-1β (β=0.84, SE 0.36; p=.02), IL-2 (β=0.78, SE 0.34; p=.03), and IL-12 p70 (β=0.88, SE 0.40; p=.03) and longitudinal postoperative elevations in GM-CSF (β=1.38, SE 0.57; p=.03), IFNγ (β=1.36, SE 0.6; p=.03), IL-1β (β=1.25, SE 0.59; p=.03), IL-7 (β=1.65, SE 0.7, p=.02), and IL-12 p70 (β=1.17, SE 0.58; p=.04). In contrast, CPSP was associated with lower baseline concentration of IL-8 (β= -0.39, SE 0.17; p=.02), and the risk of developing CPSP was elevated in patients with lower longitudinal postoperative concentrations of IL-6 (β= -0.57, SE 0.26; p=.03), IL-8 (β= -0.68, SE 0.24; p=.006), and IL-13 (β= -0.48, SE 0.22; p=.03). Furthermore, higher odds for CPSP were found for females (vs. males) for IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, and TNFα, and for pectus (vs. spine) surgery for IL-8 and IL-10.

Conclusion

We identified pro-inflammatory cytokines associated with increased acute postoperative pain and anti-inflammatory cytokines associated with lower CPSP risk, with potential to serve as predictive and prognostic biomarkers.

Macrophage epigenetic memories of early life injury drive neonatal nociceptive priming

The developing peripheral nervous and immune systems are functionally distinct from adults. These systems are vulnerable to early life injury, which influences outcomes related to nociception following subsequent injury later in life (neonatal nociceptive priming). The underpinnings of this phenomenon are largely unknown, although previous work indicates that macrophages are epigenetically trained by inflammation and injury. We found that macrophages are both necessary and partially sufficient to drive neonatal nociceptive priming possibly due to a long-lasting epigenetic remodeling. The p75 neurotrophic factor receptor (NTR) was an important effector in regulating neonatal nociceptive priming through modulation of the inflammatory profile of rodent and human macrophages. This pain memory was long lasting in females and could be transferred to a naive host to alter sex-specific pain-related behaviors. This study reveals a novel mechanism by which acute, neonatal post-surgical pain drives a peripheral immune-related predisposition to persistent pain following a subsequent injury.

Development and expansion of a pediatric transitional pain service to prevent complex chronic pain

The prevention of chronic pain is a key priority in North America and around the world. A novel pediatric Transitional Pain Service (pTPS) at the Hospital for Sick Children was established to address four main areas of need, which the authors will describe in more detail: (1) provide comprehensive multi-modal pain management and prevention techniques to children at-risk for the development of chronic pain, (2) provide opioid stewardship for children at-risk for chronic pain and their families at home after discharge, (3) facilitate continuity of pain care for children across transitions between inpatient and outpatient care settings, and (4) support caregivers to manage their child's pain at home. The pTPS works with healthcare providers, patients, and their families to address these areas of need and improve quality of life. Furthermore the service fills the gap between inpatient acute pain services and outpatient chronic pain services (accessible only once pain has persisted for >3 months). In pediatric patients who experience pain in hospital and who have been prescribed opioids, discharge to home or rehabilitation may represent a vulnerable time in which pain may persist and during which analgesic requirements may change. This offers an important opportunity to address and prevent the development of chronic pain, and to monitor opioids while ensuring alternative pain therapy is available. The authors will outline risk factors for persistent postsurgical pain, the development and implementation of a pTPS, present initial clinical outcomes andsuggest areas for future research in this evolving area of care.

Current Evidence for Biological Biomarkers and Mechanisms Underlying Acute to Chronic Pain Transition across the Pediatric Age Spectrum

Chronic pain is highly prevalent in the pediatric population. Many factors are involved in the transition from acute to chronic pain. Currently, there are conceptual models proposed, but they lack a mechanistically sound integrated theory considering the stages of child development. Objective biomarkers are critically needed for the diagnosis, risk stratification, and prognosis of the pathological stages of pain chronification. In this article, we summarize the current evidence on mechanisms and biomarkers of acute to chronic pain transitions in infants and children through the developmental lens. The goal is to identify gaps and outline future directions for basic and clinical research toward a developmentally informed theory of pain chronification in the pediatric population. At the outset, the importance of objective biomarkers for chronification of pain in children is outlined, followed by a summary of the current evidence on the mechanisms of acute to chronic pain transition in adults, in order to contrast with the developmental mechanisms of pain chronification in the pediatric population. Evidence is presented to show that chronic pain may have its origin from insults early in life, which prime the child for the development of chronic pain in later life. Furthermore, available genetic, epigenetic, psychophysical, electrophysiological, neuroimaging, neuroimmune, and sex mechanisms are described in infants and older children. In conclusion, future directions are discussed with a focus on research gaps, translational and clinical implications. Utilization of developmental mechanisms framework to inform clinical decision-making and strategies for prevention and management of acute to chronic pain transitions in children, is highlighted.

Transient Receptor Potential Ankyrin 1 (TRPA1) Methylation and Chronic Pain: A Systematic Review

BACKGROUND AND OBJECTIVE

Chronic pain represents a major global health issue in terms of psycho-physiological, therapeutic, and economic burden, not limited to adults but also to the pediatric age. Despite its great impact, its molecular mechanisms have still not been completely unraveled. Focusing on the impact of epigenetics in the pain complex trait, we assessed the association between chronic pain and the methylation pattern of TRPA1, a key gene related to pain sensitivity.

METHODS

We conducted a systematic review retrieving articles from three different databases. After deduplication, 431 items were subjected to manual screening, and then 61 articles were selected and screened again. Of these, only six were maintained for meta-analysis and analyzed using specific R packages.

RESULTS

Six articles were divided into two groups (group 1: comparison of mean methylation levels between healthy subjects and patients with chronic pain; group 2: correlation between mean methylation levels and pain sensation). A non-significant mean difference was obtained from the analysis of group 1 with a value of 3.97 (95% C.I. -7.79; 15.73). Analysis of group 2 showed a high level of variability between studies (correlation = 0.35, 95% C.I. -0.12; 0.82) due to their heterogeneity (I2 = 97%, p < 0.01).

CONCLUSIONS

Despite the high variability observed in the different studies analyzed, our results suggest that hypermethylation and increased pain sensitivity could be connected, possibly due to the variation of TRPA1 expression.

Resorption of Lumbar Disk Herniation: Mechanisms, Clinical Predictors, and Future Directions

INTRODUCTION

Resorption after lumbar disk herniation is a common yet unpredictable finding. It is hypothesized that nearly 70% of lumbar herniated nucleus pulposus (HNP) undergo the resorption to a significant degree after acute herniation, which has led to nonoperative management before surgical planning.

METHODS

This narrative review on the literature from 4 databases (MEDLINE, Cumulative Index to Nursing and Allied Health Literature, Scopus, and Cochrane) examines historical and recent advancements related to disk resorption. Studies were appraised for their description of the predictive factor (e.g., imaging or morphologic factors), pathophysiology, and treatment recommendations.

OBSERVATIONS

We reviewed 68 articles considering the possibility of resorption of lumbar HNP. Recent literature has proposed various mechanisms (inflammation and neovascularization, dehydration, and mechanical traction) of lumbar disk resorption; however, consensus has yet to be established. Current factors that increase the likelihood of resorption include the initial size of the herniation, sequestration, percentage of rim enhancement on initial gadolinium-based magnetic resonance imaging (MRI), composition of inflammatory mediators, and involvement of the posterior longitudinal ligament.

CONCLUSION

Heterogeneity in imaging and morphologic factors has led to uncertainty in the identification of which lumbar herniations will resorb. Current factors that increase the likelihood of disk resorption include the initial size of the herniation, sequestration, percentage of rim enhancement on initial MRI, composition of cellular and inflammatory mediators present, and involvement of the posterior longitudinal ligament. This review article highlights the role of disk resorption after herniation without surgical intervention and questions the role of traditional noninflammatory medications after acute herniation. Further research is warranted to refine the ideal patient profile for disk resorption to ultimately avoid unnecessary treatment, thus individualizing patient care.

Enrichment of genomic pathways based on differential DNA methylation profiles associated with knee osteoarthritis pain

Our study aimed to identify differentially methylated regions (i.e., genomic region where multiple adjacent CpG sites show differential methylation) and their enriched genomic pathways associated with knee osteoarthritis pain (KOA). We recruited cognitively healthy middle to older aged (age 45-85) adults with (n = 182) and without (n = 31) self-reported KOA pain. We also extracted DNA from peripheral blood that was analyzed using MethylationEPIC arrays. The R package minfi (Aryee et al., 2014) was used to perform methylation data preprocessing and quality control. To investigate biological pathways impacted by differential methylation, we performed pathway enrichment analysis using Ingenuity Pathway Analysis (IPA) to identify canonical pathways and upstream regulators. Annotated genes within ± 5 kb of the putative differentially methylated regions (DMRs, p < 0.05) were subjected to the IPA analysis. There was no significant difference in age, sex, study site between no pain and pain group (p > 0.05). Non-Hispanic black individuals were overrepresented in the pain group (p = 0.003). At raw p < 0.05 cutoff, we identified a total of 19,710 CpG probes, including 13,951 hypermethylated CpG probes, for which DNA methylation level was higher in the groups with highest pain grades. We also identified 5,759 hypomethylated CpG probes for which DNA methylation level was lower in the pain groups with higher pain grades. IPA revealed that pain-related DMRs were enriched across multiple pathways and upstream regulators. The top 10 canonical pathways were linked to cellular signaling processes related to immune responses (i.e., antigen presentation, PD-1, PD-L1 cancer immunotherapy, B cell development, IL-4 signaling, Th1 and Th2 activation pathway, and phagosome maturation). Moreover, in terms of upstream regulators, NDUFAF3 was the most significant (p = 8.6E-04) upstream regulator. Our findings support previous preliminary work suggesting the importance of epigenetic regulation of the immune system in knee pain and the need for future work to understand the epigenetic contributions to chronic pain.

Genetic and epigenetic mechanisms influencing acute to chronic postsurgical pain transitions in pediatrics: Preclinical to clinical evidence

Background

Chronic postsurgical pain (CPSP) in children remains an important problem with no effective preventive or therapeutic strategies. Recently, genomic underpinnings explaining additional interindividual risk beyond psychological factors have been proposed.

Aims

We present a comprehensive review of current preclinical and clinical evidence for genetic and epigenetic mechanisms relevant to pediatric CPSP.

Methods

Narrative review.

Results

Animal models are relevant to translational research for unraveling genomic mechanisms. For example, Cacng2, p2rx7, and bdnf mutant mice show altered mechanical hypersensitivity to injury, and variants of the same genes have been associated with CPSP susceptibility in humans; similarly, differential DNA methylation (H1SP) and miRNAs (miR-96/7a) have shown translational implications. Animal studies also suggest that crosstalk between neurons and immune cells may be involved in nociceptive priming observed in neonates. In children, differential DNA methylation in regulatory genomic regions enriching GABAergic, dopaminergic, and immune pathways, as well as polygenic risk scores for enhanced prediction of CPSP, have been described. Genome-wide studies in pediatric CPSP are scarce, but pathways identified by adult gene association studies point to potential common mechanisms.

Conclusions

Bench-to-bedside genomics research in pediatric CPSP is currently limited. Reverse translational approaches, use of other -omics, and inclusion of pediatric/CPSP endophenotypes in large-scale biobanks may be potential solutions. Time of developmental vulnerability and longitudinal genomic changes after surgery warrant further investigation. Emergence of promising precision pain management strategies based on gene editing and epigenetic programing emphasize need for further research in pediatric CPSP-related genomics.

Pediatric Pain Screening Tool: A Simple 9-Item Questionnaire Predicts Functional and Chronic Postsurgical Pain Outcomes After Major Musculoskeletal Surgeries

Reliable, clinic-friendly screening for Chronic postsurgical pain (CPSP) risk is unavailable. Within a prospective, observational study, we evaluated Pediatric Pain Screening Tool (PPST), a concise 9-item questionnaire, as a preoperative screening tool to identify those at higher risk for CPSP (Numerical Rating Scale > 3/10 beyond 3 months post-surgery) and poor function (disability/Functional Disability Inventory [FDI]/quality of life/ Pediatric Quality of Life) after spine fusion and Nuss procedures. Incidence of CPSP was 34.86% (38/109). We confirmed PPST scale stability, test re-test reliability (ICC = 0.68; P< .001); PPST measures were positively correlated with known CPSP risk factors (P< .001) preoperative pain (Pearson or Spearman Correlation Coefficient [SCC]:0.672), Child anxiety sensitivity index (SCC:0.357), Patient Related Outcome Measures Information System pain interference (SCC:0.569), Patient Related Outcome Measures Information System depression (SCC:0.501), Pediatric Quality of Life (SCC:-0.460) and insomnia severity index (SCC0.567). Preoperative PPST and PPST physical sub-scores (median(IQR) were higher in CPSP (2[0.5,4], 1[0,2]) compared to non-CPSP (1[0,3], 0[0,1.5]) groups (P= .026, P= .029) respectively. PPST scores/sub-scores positively correlated with higher FDI at 6 months but only PPST total and PPST psychosocial subscore correlated with higher FDI at 12 months. Based on ROC, optimal PPST cutoff for CPSP was 2 (63.9% sensitivity, 64.7% specificity). CPSP risk was high (48.94% risk) if PPST ≥ 2 (n = 47) and medium (22.81%) if PPST < 2 (n = 57) after spine/pectus surgery. General and risk-strata specific, targeted psychosocial non-pharmacological interventions, need to be studied. Findings need validation in diverse, larger cohorts. CLINICALTRIALS.GOV IDENTIFIER: NCT02998138. PERSPECTIVE: The article supports Pediatric Pain Screening Tool, a simple 9-item questionnaire, as a preoperative screening tool for CPSP and function 6-12 months after spine/pectus surgeries. PPST measures correlate with known risk factors for CPSP. Risk stratification and targeted preventive interventions in high-risk subjects are proposed.

Differential DNA methylation in Black and White individuals with chronic low back pain enrich different genomic pathways

Compared to Non-Hispanic Whites (NHWs), individuals who self-identify as Non-Hispanic Blacks (NHBs) in the United States experience more severe and disabling chronic low back pain (cLBP). We hypothesized that differences in DNA methylation (DNAm) play a role in racial disparities in cLBP.

PURPOSE

To determine the relationship between DNAm levels and racial group differences in adults with cLBP. Our study's secondary purpose was to perform a race-stratified comparison of adults with cLBP and pain-free controls and identify functional genomic pathways enriched by annotated differentially methylated genes.

PATIENTS AND METHODS

We recruited 49 NHBs and 49 NHWs (49 cLBP and 49 pain-free controls, PFCs), analyzed DNAm from whole blood using reduced representation bisulfite sequencing, and identified enriched genomic pathways.

RESULTS

Among participants with cLBP, we identified 2873 differentially methylated loci (DML; methylation differences of at least 10% and p < 0.0001), many of which were annotated to genes of importance to pain pathology. These DMLs significantly enriched pathways to involved in nociception/pain processing (Dopamine-DARPP32 Feedback in cAMP signaling, GABA Receptor Signaling, Opioid Signaling) and neuronal differentiation (e.g., Calcium Signaling, Axon Guidance Signaling, and Endocannabinoid Neuronal Synapse). Our race stratified analyses of individuals with cLBP versus PFCs revealed 2356 DMLs in NHBs and 772 DMLs in NHWs with p < 0.0001 and > 10% methylation difference. Ingenuity Pathway Analysis revealed that many pathways of significance to pain such as Corticotropin Releasing Hormone Signaling, White Adipose Tissue Browning, and GABA Receptor Signaling pathways, were more significant in NHBs than NHWs.

CONCLUSION

Even though an individual's self-identified race is a social construct, not a biological variable, racism associated with that classification affects virtually every aspect of life, including disease risk. DNAm induced alterations in stress signaling pathways may explain worse pain outcomes in NHBs.

Epigenetic signature of chronic low back pain in human T cells

Supplemental Digital Content is Available in the Text.

This study reveals sex-specific DNA methylation signatures in human T cells that discriminate chronic low back pain participants from healthy controls.

Objective:

Determine if chronic low back pain (LBP) is associated with DNA methylation signatures in human T cells that will reveal novel mechanisms and potential therapeutic targets and explore the feasibility of epigenetic diagnostic markers for pain-related pathophysiology.

Methods:

Genome-wide DNA methylation analysis of 850,000 CpG sites in women and men with chronic LBP and pain-free controls was performed. T cells were isolated (discovery cohort, n = 32) and used to identify differentially methylated CpG sites, and gene ontologies and molecular pathways were identified. A polygenic DNA methylation score for LBP was generated in both women and men. Validation was performed in an independent cohort (validation cohort, n = 63) of chronic LBP and healthy controls.

Results:

Analysis with the discovery cohort revealed a total of 2,496 and 419 differentially methylated CpGs in women and men, respectively. In women, most of these sites were hypomethylated and enriched in genes with functions in the extracellular matrix, in the immune system (ie, cytokines), or in epigenetic processes. In men, a unique chronic LBP DNA methylation signature was identified characterized by significant enrichment for genes from the major histocompatibility complex. Sex-specific polygenic DNA methylation scores were generated to estimate the pain status of each individual and confirmed in the validation cohort using pyrosequencing.

Conclusion:

This study reveals sex-specific DNA methylation signatures in human T cells that discriminates chronic LBP participants from healthy controls.

Epigenetics and postsurgical pain: A scoping review

OBJECTIVE

Multiple factors are involved in the physiology and variability of postsurgical pain, a great part of which can be explained by genetic and environmental factors and their interaction. Epigenetics refers to the mechanism by which the environment alters the stability and expression of genes. We conducted a scoping review to examine the available evidence in both animal models and clinical studies on epigenetic mechanisms involved in regulation of postsurgical and chronic postsurgical pain.

METHODS

The Arksey & ÓMalley framework and the PRISMA-ScR (Preferred Reporting Items for Systematic Review and Meta-Analysis, scoping reviews extension) guidelines were used. The PubMed, Web of Science and Google Scholar databases were searched, and the original articles cited in reviews located through the search were also reviewed. English-language articles without time limits were retrieved. Articles were selected if the abstract addressed information on the epigenetic or epigenomic mechanisms, histone, or DNA methylation and microribonucleic acids involved in postsurgical and chronic postsurgical pain in animal models and clinical studies.

RESULTS

The initial search provided 174 articles, and 81 were used. The available studies to date, mostly in animal models, have shown that epigenetics contributes to regulation of gene expression in the pathways involved in postsurgical pain and in maintaining long-term pain.

CONCLUSION

Research on possible epigenetic mechanisms involved in postsurgical pain and chronic postsurgical pain in humans is scarce. In view of the evidence available in animal models, there is a need to evaluate epigenetic pain mechanisms in the context of human and clinical studies.

Methylation quantitative trait locus analysis of chronic postsurgical pain uncovers epigenetic mediators of genetic risk

Background: Overlap of pathways enriched by single nucleotide polymorphisms and DNA-methylation underlying chronic postsurgical pain (CPSP), prompted pilot study of CPSP-associated methylation quantitative trait loci (meQTL). Materials & methods: Children undergoing spine-fusion were recruited prospectively. Logistic-regression for genome- and epigenome-wide CPSP association and DNA-methylation-single nucleotide polymorphism association/mediation analyses to identify meQTLs were followed by functional genomics analyses. Results: CPSP (n = 20/58) and non-CPSP groups differed in pain-measures. Of 2753 meQTLs, DNA-methylation at 127 cytosine-guanine dinucleotides mediated association of 470 meQTLs with CPSP (p < 0.05). At PARK16 locus, CPSP risk meQTLs were associated with decreased DNA-methylation at RAB7L1 and increased DNA-methylation at PM20D1. Corresponding RAB7L1/PM20D1 blood eQTLs (GTEx) and cytosine-guanine dinucleotide-loci enrichment for histone marks, transcription factor binding sites and ATAC-seq peaks suggest altered transcription factor-binding. Conclusion: CPSP-associated meQTLs indicate epigenetic mechanisms mediate genetic risk. Clinical trial registration: NCT01839461, NCT01731873 (ClinicalTrials.gov).

Postoperative Pain Management in Pediatric Spinal Fusion Surgery for Idiopathic Scoliosis

This article reviews and summarizes current evidence and knowledge gaps regarding postoperative analgesia after pediatric posterior spine fusion for adolescent idiopathic scoliosis, a common procedure that results in severe acute postoperative pain. Inadequate analgesia may delay recovery, cause patient dissatisfaction, and increase chronic pain risk. Despite significant adverse effects, opioids are the analgesic mainstay after scoliosis surgery. However, growing emphasis on opioid minimization and enhanced recovery has increased adoption of multimodal analgesia (MMA) regimens. While opioid adverse effects remain a concern, MMA protocols must also consider risks and benefits of adjunct medications. We discuss use of opioids via different administration routes and elaborate on the effect of MMA components on opioid/pain and recovery outcomes including upcoming regional analgesia. We also discuss risk for prolonged opioid use after surgery and chronic post-surgical pain risk in this population. Evidence supports use of neuraxial opioids at safe doses, low-dose ketorolac, and methadone for postoperative analgesia. There may be a role for low-dose ketamine in those who are opioid-tolerant or have chronic pain, but the evidence for preoperative gabapentinoids and intravenous lidocaine is currently insufficient. There is a need for further studies to evaluate pediatric-specific optimal MMA dosing regimens after scoliosis surgery. Questions remain regarding how best to prevent acute opioid tolerance, opioid-induced hyperalgesia, and chronic postsurgical pain. We anticipate that this timely update will enable clinicians to develop efficient pain regimens and provide impetus for future research to optimize recovery outcomes after spine fusion.

A Conceptual Model of Biopsychosocial Mechanisms of Transition from Acute to Chronic Postsurgical Pain in Children and Adolescents

Acute and chronic pain are highly prevalent and impactful consequences of surgery across the lifespan, yet a comprehensive conceptual model encompassing biopsychosocial factors underlying acute to chronic pain transition is lacking, particularly in youth. Building on prior chronic postsurgical pain models, we propose a new conceptual model of biopsychosocial mechanisms of transition from acute to chronic postsurgical pain. This review aims to summarize existing research examining key factors underlying acute to chronic postsurgical pain transition in order to guide prevention and intervention efforts aimed at addressing this health issue in children. As pain transitions from acute nociceptive pain to chronic pain, changes in the peripheral and central nervous system contribute to the chronification of pain after surgery. These changes include alterations in sensory pain processing and psychosocial processes (psychological, behavioral, and social components), which promote the development of chronic pain. Patient-related premorbid factors (eg, demographic factors, genetic profile, and medical factors such as premorbid pain) may further modulate these changes. Factors related to acute injury and recovery (eg, surgical and treatment factors), as well as biological response to surgery (eg, epigenetic, inflammatory, and endocrine factors), may also influence this process. Overall, longitudinal studies examining temporal pathways of biopsychosocial processes including both risk and resiliency factors will be essential to identify the mechanisms involved in the transition from acute to chronic pain. Research is also needed to unravel connections between the acute pain experience, opioid exposure, and sensory pain processing during acute to chronic pain transition. Furthermore, future studies should include larger and more diverse samples to more fully explore risk factors in a broader range of pediatric surgeries. The use of conceptual models to guide intervention approaches targeting mechanisms of transition from acute to chronic pain will significantly advance this field and improve outcomes for children and adolescents undergoing surgery.

Time course of DNA methylation in pain conditions: From experimental models to humans

BACKGROUND AND OBJECTIVE

Throughout the last decade, research has uncovered associations between pain and epigenetic alterations caused by environmental factors. Specifically, studies have demonstrated correlations between pain conditions and altered DNA methylation patterns. Thus, DNA methylation has been revealed as a possible modulator or contributor to pain conditions, providing a potential therapeutic target for treatment by DNA methylation modification. To develop such treatments, it is necessary to clarify a wide number of aspects on how DNA methylation affects pain perception; first and foremost, the temporal dynamics. The objective of the present review is to provide an overview of current knowledge on temporal dynamics of DNA methylation in response to pain, and to investigate if a timeframe can be established based on the data of currently published studies.

DATABASES AND DATA TREATMENT

PubMed, MEDLINE, Google Scholar and Embase were searched comprehensively for studies of DNA methylation in neuropathic, inflammatory and alternative animal pain models, and in chronic pain patients including Complex Regional Pain Syndrome, chronic postsurgical pain, chronic widespread pain, fibromyalgia and Crohn's disease.

RESULTS

We identified 34 articles highlighting variations in temporal dynamics of DNA methylation across species and between different types of pain. These studies represent a starting point to uncover new insights in the DNA methylation time course in pain.

CONCLUSIONS

No timeframe can currently be made for the DNA methylation response to pain in any of the reviewed conditions, highlighting an important focus area for future research.

DNA methylation biomarkers of future health outcomes in children

Biomarkers which predict future health outcomes are key to the goals of precision health. Such biomarkers do not have to be involved in the causal pathway of a disease, and their performance is best assessed using statistical tests of clinical performance and evaluation of net health impact. DNA methylation is the most commonly studied epigenetic process and represents a potential biomarker of future health outcomes. We review 25 studies in non-oncological paediatric conditions where DNA methylation biomarkers of future health outcomes are assessed. Whilst a number of positive findings have been described, the body of evidence is severely limited by issues with outcome measures, tissue-specific samples, accounting for sample cell type heterogeneity, lack of appropriate statistical testing, small effect sizes, limited validation, and no assessment of net health impact. Future studies should concentrate on careful study design to overcome these issues, and integration of DNA methylation data with other 'omic', clinical, and environmental data to generate the most clinically useful biomarkers of paediatric disease.

The etiological contribution of GABAergic plasticity to the pathogenesis of neuropathic pain

Neuropathic pain developing after peripheral or central nerve injury is the result of pathological changes generated through complex mechanisms. Disruption in the homeostasis of excitatory and inhibitory neurons within the central nervous system is a crucial factor in the formation of hyperalgesia or allodynia occurring with neuropathic pain. The central GABAergic pathway has received attention for its extensive distribution and function in neural circuits, including the generation and development of neuropathic pain. GABAergic inhibitory changes that occur in the interneurons along descending modulatory and nociceptive pathways in the central nervous system are believed to generate neuronal plasticity, such as synaptic plasticity or functional plasticity of the related genes or proteins, that is the foundation of persistent neuropathic pain. The primary GABAergic plasticity observed in neuropathic pain includes GABAergic synapse homo- and heterosynaptic plasticity, decreased synthesis of GABA, down-expression of glutamic acid decarboxylase and GABA transporter, abnormal expression of NKCC1 or KCC2, and disturbed function of GABA receptors. In this review, we describe possible mechanisms associated with GABAergic plasticity, such as central sensitization and GABAergic interneuron apoptosis, and the epigenetic etiologies of GABAergic plasticity in neuropathic pain. Moreover, we summarize potential therapeutic targets of GABAergic plasticity that may allow for successful relief of hyperalgesia from nerve injury. Finally, we compare the effects of the GABAergic system in neuropathic pain to other types of chronic pain to understand the contribution of GABAergic plasticity to neuropathic pain.

DNA Methylation May be Involved in the Analgesic Effect of Hyperbaric Oxygen via Regulating FUNDC1

Background

Neuropathic pain (NP) is a type of chronic pain which lacks predictable, effective, and safe therapeutic options. We investigated the role of hyperbaric oxygen (HBO) in expression of FUN14 domain-containing 1 (FUNDC1), which is associated with DNA methylation.

Methods

We randomly divided rats into four groups: sham operation (S), S + HBO, chronic constriction injury (CCI), and CCI + HBO. Lumbar (L)4 and L5 dorsal root ganglia (DRGs) were used to assess expression of DNA methyltransferase (DNMT)1, DNMT3a, and DNMT3b by western blotting and RT-PCR. Pain-related behaviors were evaluated using mechanical withdrawal threshold and thermal withdrawal latency analysis. Western blotting was also used to assess expression of FUNDC1, BCL2, and adenovirus E1B19 kDa-interacting protein 3-like (NIX) and BCL2 and adenovirus E1B19 kDa-interacting protein3 (BNIP3). And we also examined the changes of FUNDC1 with immunofluorescence. Nonnucleoside DNA methyltransferase inhibitor RG108 was administered prior to CCI. The pain-related behavior and western blotting changes were examined in all groups.

Results

DNMT3a expression was higher on day 14 after CCI. HBO downregulated DNMT3a mRNA and protein expression, but not those of DNMT1 and DNMT3b. HBO increased pain-related behavior significantly, while it was down-regulated by RG108. In HBO groups, FUNDC1, NIX, and BNIP3 expression was upregulated more significantly than in the CCI group. In addition, FUNDC1 protein colocalized with NeuN and rarely with glutamine synthetase. However, expression was reduced when RG108 was administered. Immunofluorescence showed that FUNDC1 was upregulated after HBO treatment.

Conclusion

Our findings suggest that DNA methylation is involved in the analgesic effect of HBO via the regulation of FUNDC1.

Association between neuropathic pain characteristics and DNA methylation of transient receptor potential ankyrin 1 in human peripheral blood

Elucidation of epigenetic mechanisms correlating with neuropathic pain in humans is crucial for the prevention and treatment of this treatment-resistant pain state. In the present study, associations between neuropathic pain characteristics and DNA methylation of the transient receptor potential ankyrin 1 (TRPA1) gene were evaluated in chronic pain patients and preoperative patients. Pain and psychological states were prospectively assessed in patients who suffered chronic pain or were scheduled for thoracic surgery. Neuropathic characteristics were assessed using the Douleur Neuropathique 4 (DN4) questionnaire. DNA methylation levels of the CpG islands in the TRPA1 gene were examined using whole blood. Forty-eight adult patients were enrolled in this study. Increases in DNA methylation rates at CpG -51 showed positive correlations with increases in the DN4 score both in preoperative and chronic pain patients. Combined methylation rates at CpG -51 in these patients also significantly increased together with increase in DN4 scores. Neuropathic pain characteristics are likely associated with methylation rates at the promoter region of the TRPA1 gene in human peripheral blood.

Enrichment of genomic pathways based on differential DNA methylation profiles associated with chronic musculoskeletal pain in older adults: An exploratory study

Our study aimed to identify differentially methylated CpGs/regions and their enriched genomic pathways associated with underlying chronic musculoskeletal pain in older individuals. We recruited cognitively healthy older adults with (n = 20) and without (n = 9) self-reported musculoskeletal pain and collected DNA from peripheral blood that was analyzed using MethylationEPIC arrays. We identified 31,739 hypermethylated CpG and 10,811 hypomethylated CpG probes (ps ≤ 0.05). All CpG probes were clustered into 5966 regions, among which 600 regions were differentially methylated at p ≤ 0.05 level, including 294 hypermethylated regions and 306 hypomethylated regions (differentially methylated regions). Ingenuity pathway enrichment analysis revealed that the pain-related differentially methylated regions were enriched across multiple pathways. The top 10 canonical pathways were linked to cellular signaling processes related to immune responses (i.e. antigen presentation, programed cell death 1 receptor/PD-1 ligand 1, interleukin-4, OX40 signaling, T cell exhaustion, and apoptosis) and gamma-aminobutyric acid receptor signaling. Further, Weighted Gene Correlation Network Analysis revealed a comethylation network module in the pain group that was not preserved in the control group, where the hub gene was the cyclic adenosine monophosphate-dependent transcription factor ATF-2. Our preliminary findings provide new epigenetic insights into the role of aberrant immune signaling in musculoskeletal pain in older adults while further supporting involvement of dysfunctional GABAergic signaling mechanisms in chronic pain. Our findings need to be urgently replicated in larger cohorts as they may serve as a basis for developing and targeting future interventions.

Systematic Review and Meta-Analysis of Genetic Risk of Developing Chronic Postsurgical Pain

Chronic postsurgical pain (CPSP) is a significant detriment to postsurgical recovery and a risk factor for prolonged opioid use. Emerging evidence suggests the estimated heritability for chronic pain is 45% and that genetic factors partially explain individual susceptibility to CPSP. The aim of this study was to systematically review, assess quality, and summarize the studies in humans that have investigated genetic factors associated with CPSP. We also conducted a meta-analysis to derive a single effect size for evaluable genetic associations with CPSP. Our comprehensive literature search included review of 21 full-text articles evaluating variants of 69 genes for association with CPSP. We found significant gene variant associations reported for variants/haplotypes of 26 genes involved in neurotransmission, pain signaling, immune responses and neuroactive ligand-receptor interaction, with CPSP. Six variants of 5 genes (COMT: rs4680 and rs6269, OPRM1: rs1799971, GCH1: rs3783641, KCNS1: rs734784 and TNFA: rs1800629), were evaluated by more than one study and were included in the meta-analysis. At rs734784 (A>G) of KCNS1, presence of G allele marginally increased risk of CPSP (Additive genetic model; Odds ratio: 1.511; 95% CI 1-2.284; P value: .050), while the other variants did not withstand meta-analyses criteria. Our findings demonstrate the role of genetic factors with different functions in CPSP, and also emphasize that single genetic factors have small effect sizes in explaining complex conditions like CPSP. Heterogeneity in surgical cohorts, population structure, and outcome definitions, as well as small number of available studies evaluating same variants, limit the meta-analysis. There is a need for large-scale, homogenous, replication studies to validate candidate genes, and understand the underlying biological networks underpinning CPSP. PERSPECTIVE: Our systematic review comprehensively describes 21 studies evaluating genetic association with CPSP, and limitations thereof. A meta-analysis of 6 variants (5 genes) found marginally increased risk for CPSP associated with rs734784 A>G of the potassium voltage-gated channel gene (KCNS1). Understanding genetic predisposition for CPSP will enable prediction and personalized management.

Epigenetic aging is associated with clinical and experimental pain in community-dwelling older adults

Gerontological research reveals considerable interindividual variability in aging phenotypes, which has motivated research efforts to identify “aging biomarkers.” Aging biomarkers are used to calculate biological age, which are better predictors of disease risk and residual lifespan when compared to chronological age alone. Emerging evidence using the epigenetic clock as an aging biomarker supports highly reliable individualized predictions about future health. This study aimed to determine whether an epigenetic aging biomarker was associated with chronic pain in older adults (60–83 years old). A subset of participants (n = 29) in the Neuromodulatory Examination of Pain and Mobility Across the Lifespan study underwent a blood draw, demographic, psychological, cognitive, and pain assessments. We estimated Horvath’s epigenetic clock and calculated the difference between epigenetic age and chronological age that has been previously reported to predict overall mortality risk. Older individuals without chronic pain (n = 9) had significantly “younger” epigenetic age compared to those with chronic pain (n = 20, p < 0.05). Older epigenetic age was associated with greater pain during daily activities (r = 0.494, p = 0.010) and anatomical pain sites (r = 0.741, p < 0.001) but not pain frequency/duration. An older epigenetic age was also associated with higher vibratory detection thresholds (r = 0.490, p = 0.021), heat pain thresholds (r = −0.478, p = 0.028), and pressure pain thresholds at the trapezius (r = −0.571, p = 0.006) but not thermal detection, pressure pain at the quadriceps or pain inhibition (p’s > 0.05). Epigenetic aging was associated with greater emotional stability (r = −0.461, p = 0.027), conscientiousness (r = −0.549, p = 0.007), and lower extraversion (r = 0.414, p = 0.049) but not depression or affect (p’s > 0.05). Epigenetic aging was also associated with lower episodic (r = −0.698, p = 0.001) and working memory (r = −0.760, p < 0.001). Our findings suggest that chronic pain is associated with accelerated epigenetic aging in healthy, community-dwelling older individuals, and future studies with larger samples are needed to confirm our findings. An aging biomarker such as the epigenetic clock may help identify people with chronic pain at greater risk of functional decline and poorer health outcomes.