Examining Physical and Cognitive Function in Chronic Low Back Pain Through the Use of a Multisystem Resilience Framework

OBJECTIVES

Chronic pain results in significant impairment in older adults, yet some individuals maintain adaptive functioning. Limited research has considered the role of positive resources in promoting resilience among older adults. Likewise, these factors have largely been examined independently. We aimed to identify resilience domains based on biopsychosocial factors and explore whether resilience phenotypes vary across sleep disturbance, fatigue, and cognitive function.

METHODS

Sixty adults (ages ≥60 years) with chronic low back pain completed measures of psychological, health, and social functioning. On the basis of previously published analyses, principal-components analysis was conducted to create composite domains for these measures, followed by cluster analysis to identify phenotypes.

RESULTS

Four profiles emerged: Cluster 1, with high levels of psychosocial and health-related functioning; Cluster 2, with high health-related functioning and low psychosocial functioning; Cluster 3, with high psychosocial functioning and poorer health; and Cluster 4, with low levels of functioning across all domains. Significant differences across cluster membership emerged for sleep disturbance (ηp2 = 0.29), fatigue (ηp2 = 0.29), and cognitive abilities (ηp2 = 0.47). Individuals with the highest levels of resilience demonstrated more optimal outcomes in sleep and fatigue (P values ≤0.001) than did individuals with a less resilient phenotype. Furthermore, the High-Resilience group (Cluster 1) and the High Psychosocial / Low Health group (Cluster 3) had lower cognitive impairment than did the High Health / Low Psychosocial group (Cluster 2) and the Low-Resilience group (Cluster 4) (P values ≤0.009).

CONCLUSIONS

A higher array of protective resources could buffer against the negative sequelae associated with chronic low back pain. These exploratory findings support the multidimensional nature of resilience and suggest that targeting resilience from a multisystem perspective might help to optimize interventions for older adults with chronic pain.

Protocol for a pilot and feasibility randomized-controlled trial of four weeks of oral γ-aminobutyric acid (GABA) intake and its effect on pain and sleep in middle-to-older aged adults

Approximately 1.71 billion people globally live with musculoskeletal pain conditions, including low back pain, knee pain, and neck pain Cieza et al. (2020). In the US, an estimated 20.4% of U.S. adult had chronic pain and 8.0% of U.S. adults had high-impact chronic pain, with higher prevalence associated with advancing age Dahlhamer et al. (2018). On the other hand, between 50 and 70 million US adults have a sleep disorder (American Sleep Association). Although the link between sleep and pain is widely established, the neurobiological mechanisms underlying this relationship have yet to be fully elucidated, specifically within an aged population. As currently available sleep and chronic pain therapies are only partially effective, novel treatment approaches are urgently needed. Given the potential mechanistic role of γ-aminobutyric acid (GABA) in both conditions, and the availability of GABA supplements over the counter, the present proposal will determine the feasibility and acceptability of oral GABA administration in middle-to-older aged adults with chronic pain and sleep disorders as well as characterize the potential neurobiological mechanisms involved in both conditions. Results from the present investigation using a parallel, double-blinded, placebo-controlled study will provide novel preliminary information needed for future translational pain and sleep research.

A rose by another name? Characteristics that distinguish headache secondary to temporomandibular disorder from headache that is comorbid with temporomandibular disorder

ABSTRACT

Co-occurring pain conditions that affect overlapping body regions are complicated by the distinction between primary vs secondary pain conditions. We investigate the occurrence of headache and painful temporomandibular disorder (TMD) in a community-based, cross-sectional study of US adults in the Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA-II) study. A specific goal was to determine whether headache attributed to TMD is separable from primary headache. Using DC/TMD and International Classification of Headache Disorders-third edition criteria, 3 groups of individuals were created: (a) headache without TMD; (b) headache comorbid with TMD; and (c) headache attributed to TMD. Regression models compared study groups according to demographic and comorbid characteristics, and post hoc contrasts tested for differences. Descriptive statistics and Cohen d effect size were computed, by group, for each predictor variable. Differences in continuous predictors were analyzed using one-way analysis of variance. Nearly all demographic and comorbid variables distinguished the combined headache and TMD groups from the group with headache alone. Relative to the reference group with primary headache alone, markers related to headache, TMD, somatic pain processing, psychosocial, and health conditions were substantially greater in both headache comorbid with TMD and headache attributed to TMD, attesting to their qualitative similarities. However, effect sizes relative to the reference group were large for headache comorbid with TMD and larger again for headache attributed to TMD, attesting to their separability in quantitative terms. In summary, the presence of overlapping painful TMD and headache adds substantially to the biopsychosocial burden of headache and points to the importance of comprehensive assessment and differential management.

Efficiency of pain inhibition and facilitation of fibromyalgia patients is not different from healthy controls: Relevance of sensitivity-adjusted test stimuli

Background

Pain is a dynamic phenomenon dependent on the balance of endogenous excitatory and inhibitory systems, which can be characterized by quantitative sensory testing. Many previous studies of pain modulatory capacity of patients with fibromyalgia syndrome (FM) have reported decreased pain inhibition or increased pain facilitation. This is the first study to assess pain modulation, including conditioned pain modulation (CPM) and temporal pain summation, in the same healthy control (HC) and FM participants.

Methods

Only sensitivity-adjusted stimuli were utilized for testing of conditioned pain modulation (CPM) and temporal pain summation in 23 FM patients and 28 HC. All subjects received sensitivity-adjusted ramp-hold (sRH) during testing of pain facilitation (temporal summation) and pain inhibition (CPM). CPM efficacy was evaluated with test stimuli applied either concurrently or after application of the conditioning stimulus. Finally, the effects of CPM on pressure pain thresholds were tested.

Results

FM subjects required significantly less intense test and conditioning stimuli than HC participants to achieve standardized pain ratings of 50 ± 10 numerical rating scale (NRS) (p = 0.03). Using such stimuli, FM subjects' temporal pain summation and CPM efficacy was not significantly different from HC (all p > 0.05), suggesting similar pain facilitation and inhibition. Furthermore, the CPM efficacy of FM and HC participants was similar regardless of whether the test stimuli were applied during or after the conditioning stimulus (p > 0.05).

Conclusion

Similar to previous studies, FM participants demonstrated hyperalgesia to heat, cold, and mechanical stimuli. However, using only sensitivity-adjusted stimuli during CPM and temporal summation testing, FM patients demonstrated similarly effective pain inhibition and facilitation than HC, suggesting that their pain modulation is not abnormal.

Pain interference mediates the association between epigenetic aging and grip strength in middle to older aged males and females with chronic pain

Introduction

Chronic pain is one of the leading causes of disability that may accelerate biological aging and reduce physical function. Epigenetic clocks provide an estimate of how the system ages and can predict health outcomes such as physical function. Physical function declines may be attributed to decreases in muscle quality due to disuse that can be measured quickly and noninvasively using grip strength. The purpose of this study was to explore the associations among self-reported pain, grip strength, and epigenetic aging in those with chronic pain.

Methods

Participants (57.91 ± 8.04 years) completed pain questionnaires, a blood draw and hand grip strength task. We used an epigenetic clock previously associated with knee pain (DNAmGrimAge), and used the subsequent difference of predicted epigenetic age from chronological age (DNAmGrimAge-Difference).

Results

Exploratory pathway analyses revealed that pain intensity mediated the association between DNAmGrimAge-difference and handgrip strength in males only (β = -0.1115; CI [-0.2929, -0.0008]) and pain interference mediated the association between DNAmGrimAge-difference and handgrip strength in males β = -0.1401; CI [-0.3400, -0.0222]), and females (β = -0.024; CI [-0.2918, -0.0020]).

Discussion

Chronic knee pain may accelerate epigenetic aging processes that may influence handgrip strength in older age adults. Chronic pain could be a symptom of the aging body thus contributing to declines in musculoskeletal function in later life.

Circulating Polyunsaturated Fatty Acids and Pain Intensity in Five Chronic Pain Conditions

Pain intensity is well-known to be influenced by a wide range of biobehavioral variables. Nutritional factors, however, have not been generally considered for their potential importance. This cross-sectional study examined associations between erythrocyte omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFAs) and pain intensity in 605 adults. Pain intensity was computed on a 0 to 100 numeric rating scale from questions about 5 chronic pain conditions: orofacial pain, headache, low back pain, irritable bowel syndrome, and bodily pain. For each pain condition, multiple linear regression tested the hypothesis that a higher ratio of n-6 arachidonic acid to the sum of n-3 eicosapentaenoic acid and docosahexaenoic acid (AA/(EPA+DHA) was associated with greater pain intensity. In covariate-adjusted analysis, orofacial pain intensity increased 5.7 points (95% CI: 1.4, 9.9) per unit increase in n-6/n-3 PUFA ratio. Likewise, a 1 unit increase in n-6/n-3 PUFA ratio was associated with significant increases in pain intensity (range 5-8 points) of headache pain, low back pain, and bodily pain, but not abdominal pain. Separate multiple linear regression models investigated the independent strength of association of individual PUFAs to the intensity of each pain condition. Overall, n-3 docosahexaenoic acid was most strongly, and inversely, associated with pain intensity. PERSPECTIVE: A higher ratio of n-6/n-3 long-chain polyunsaturated fatty acids was associated greater pain intensity for orofacial pain, headache, low back pain, and bodily pain, but not abdominal pain. The n-6/n-3 PUFA ratio was more consistently associated with pain intensity than any individual constituent of the long-chain PUFA ratio.

Self-reported pain and fatigue are associated with physical and cognitive function in middle to older-aged adults

Persistent fatigue is often reported in those with chronic musculoskeletal pain. Separately, both chronic pain and chronic fatigue contribute to physical and cognitive decline in older adults. Concurrent pain and fatigue symptoms may increase disability and diminish quality of life, though little data exist to show this. The purpose of this study was to examine associations between self-reported pain and fatigue, both independently and combined, with cognitive and physical function in middle-older-aged adults with chronic knee pain. Using a cross-sectional study design participants (n = 206, age 58.0 ± 8.3) completed questionnaires on pain and fatigue, a physical performance battery to assess physical function, and the Montreal Cognitive Assessment. Hierarchical regressions and moderation analyses were used to assess the relationship between the variables of interest. Pain and fatigue both predicted physical function (β = -0.305, p < 0.001; β = -0.219, p = 0.003, respectively), however only pain significantly predicted cognitive function (β = -0.295, p <0.001). A centered pain*fatigue interaction was a significant predictor of both cognitive function (β = -0.137, p = 0.049) and physical function (β = -0.146, p = 0.048). These findings indicate that self-reported fatigue may contribute primarily to decline in physical function among individuals with chronic pain, and less so to decline in cognitive function. Future studies should examine the impact of both cognitive and physical function decline together on overall disability and health.

Brain predicted age difference mediates pain impact on physical performance in community dwelling middle to older aged adults

The purpose of the study was to examine associations between physical performance and brain aging in individuals with knee pain and whether the association between pain and physical performance is mediated by brain aging. Participants (n=202) with low impact knee pain (n=111), high impact knee pain (n=60) and pain-free controls (n=31) completed self-reported pain, magnetic resonance imaging (MRI), and a Short Physical Performance Battery (SPPB) that included balance, walking, and sit to stand tasks. Brain predicted age difference, calculated using machine learning from MRI images, significantly mediated the relationships between walking and knee pain impact (CI: -0.124; -0.013), walking and pain-severity (CI: -0.008; -0.001), total SPPB score and knee pain impact (CI: -0.232; -0.025), and total SPPB scores and pain-severity (CI: -0.019; -0.001). Brain-aging begins to explain the association between pain and physical performance, especially walking. This study supports the idea that a brain aging prediction can be calculated from shorter duration MRI sequences and possibly implemented in a clinical setting to be used to identify individuals with pain who are at risk for accelerated brain atrophy and increased likelihood of disability.

Vitamin D Metabolism Genes Are Differentially Methylated in Individuals with Chronic Knee Pain

INTRODUCTION

Recent evidence suggests that vitamin D may interact with the epigenome and play a role in the pain experience. In order for proper functioning to occur, there must be an adequate level of vitamin D present, made possible by enzymatic reactions that allow vitamin D to be biologically active. The purpose of this study was to explore the epigenetic landscape of genes involved in vitamin D metabolism in individuals with and without chronic knee pain.

METHODS

Community-dwelling individuals recruited as part of a larger study focused on knee pain provided demographic, clinical, and pain-related information, as well as an intravenous blood sample to determine DNA methylation levels at CpG sites.

RESULTS

There were differences in DNA methylation between those with and without pain in genes that code for enzymes related to vitamin D metabolism: CYP27B1 (1-α-hydroxylase). There was also hypermethylation on the gene that codes for the vitamin D receptor (VDR).

CONCLUSIONS

The presence of chronic pain is associated with epigenetic modifications in genes responsible for the expression of enzymes involved in vitamin D metabolism and cellular function. These results lay groundwork in understanding the mechanism underlying the association between vitamin D and chronic pain.

Elucidating factors contributing to disparities in pain-related experiences among adults with or at risk for knee osteoarthritis

Background and purpose

We and others have reported ethnic/race group differences in clinical pain, physical function, and experimental pain sensitivity. However, recent research indicates that with consideration for socioenvironmental factors, ethnicity/race differences become less or non-significant. Understanding of factors contributing to pain inequities are needed. Guided by the NIA and NIMHD Health Disparities Research Frameworks, we evaluate the contributions of environmental and behavioral factors on previously reported ethnic/race group differences in: (1) clinical pain, (2) physical function, and (3) experimental pain in individuals with knee pain.

Methods

Baseline data from Understanding of Pain and Limitations in Osteoarthritis Disease (UPLOAD) and UPLOAD-2 studies were analyzed. Participants were adults 45 to 85 years old who self-reported as non-Hispanic white (NHW) or black (NHB) with knee pain. A health assessment and quantitative sensory testing were completed. Sociodemographics, environmental, health, clinical and experimental pain, and physical functioning measures were included in nested regressions.

Results

Pooled data from 468 individuals, 57 ± 8 years of age, 63% women, and 53% NHB adults. As NHB adults were younger and reported greater socioenvironmental risk than the NHW adults, the term sociodemographic groups is used. With inclusion of recognized environmental and behavioral variables, sociodemographic groups remained a significant predictor accounting for <5% of the variance in clinical pain and physical function and <10% of variance in experimental pain.

Conclusion

The incorporation of environmental and behavioral factors reduced relationships between sociodemographic groups and pain-related outcomes. Pain sites, BMI, and income were significant predictors across multiple models. The current study adds to a body of research on the complex array of factors contributing to disparities in pain-related outcomes.

Biopsychosocial influence on shoulder pain: results from a randomized preclinical trial of exercise-induced muscle injury

ABSTRACT

Prior cohort studies validated that a subgroup defined by a specific COMT genotype and pain catastrophizing is at increased risk for heightened responses to exercise-induced or surgically induced shoulder pain. In this clinical trial, we used our preclinical model of exercise-induced muscle injury and pain to test the efficacy of interventions matched to characteristics of this high-risk subgroup (ie, personalized medicine approach). Potential participants provided informed consent to be screened for eligibility based on subgroup membership and then, as appropriate, were enrolled into the trial. Participants (n = 261) were randomized to 1 of 4 intervention groups comprised of pharmaceutical (propranolol or placebo) and informational (general education or psychologic intervention) combinations. After muscle injury was induced, participants received randomly assigned treatment and were followed for the primary outcome of shoulder pain intensity recovery over 4 consecutive days. Recovery rates were 56.4% (placebo and psychologic intervention), 55.4% (placebo and general education), 62.9% (propranolol and psychologic intervention), and 56.1% (propranolol and general education). No statistical differences were found between intervention groups in the primary analyses. Additional analyses found no differences between these intervention groups when shoulder pain duration was an outcome, and no differential treatment responses were detected based on sex, race, or level of pain catastrophizing. This trial indicates that these treatments were not efficacious for this high-risk subgroup when shoulder pain was induced by exercise-induced muscle injury. Accordingly, this phenotype should only be used for prognostic purposes until additional trials are completed in clinical populations.

Conscious connected breathing with breath retention intervention in adults with chronic low back pain: protocol for a randomized controlled pilot study

BACKGROUND

Chronic pain is a major source of human suffering, and chronic low back pain (cLBP) is among the most prevalent, costly, and disabling of pain conditions. Due to the significant personal and societal burden and the complex and recurring nature of cLBP, self-management approaches that can be practiced at home are highly relevant to develop and test. The respiratory system is one of the most integrated systems of the body, and breathing is bidirectionally related with stress, emotion, and pain. Thus, the widespread physiological and psychological impact of breathing practices and breathwork interventions hold substantial promise as possible self-management strategies for chronic pain. The primary aim of the current randomized pilot study is to test the feasibility and acceptability of a conscious connected breathing with breath retention intervention compared to a sham control condition.

METHODS

The rationale and procedures for testing a 5-day conscious connected breathing with breath retention intervention, compared to a deep breathing sham control intervention, in 24 adults (18-65 years) with cLBP is described. Both interventions will be delivered using standardized audio recordings and practiced over 5 days (two times in-person and three times at-home), and both are described as Breathing and Attention Training to reduce possible expectancy and placebo effects common in pain research. The primary outcomes for this study are feasibility and acceptability. Feasibility will be evaluated by determining rates of participant recruitment, adherence, retention, and study assessment completion, and acceptability will be evaluated by assessing participants' satisfaction and helpfulness of the intervention. We will also measure other clinical pain, psychological, behavioral, and physiological variables that are planned to be included in a follow-up randomized controlled trial.

DISCUSSION

This will be the first study to examine the effects of a conscious connected breathing with breath retention intervention for individuals with chronic pain. The successful completion of this smaller-scale pilot study will provide data regarding the feasibility and acceptability to conduct a subsequent trial testing the efficacy of this breathing self-management practice for adults with cLBP.

TRIAL REGISTRATION

Clinicaltrials.gov, identifier NCT04740710 . Registered on 5 February 2021.

More Problems, More Pain: The Role of Chronic Life Stressors and Racial/Ethnic Identity on Chronic Pain Among Middle-Aged and Older Adults in the United States

There is a high prevalence of chronic pain among middle-aged and older adults in the United States. Chronic life stressors have been shown to have detrimental consequences for myriad health conditions, including chronic pain. However, there is limited evidence on the types of chronic life stressors that affect middle-aged and older adults and how these stressors influence the chronic pain burden in this population. Moreover, the interaction between chronic life stressors and racial/ethnic identity remains poorly understood as it relates to chronic pain. The current analysis used the 2018 Health and Retirement Study to investigate relationships between chronic life stressors and odds to experience any chronic pain and high-impact chronic pain. Chronic life stressors were characterized, overall and by racial/ethnic identity, and the main and interaction effects were calculated to evaluate relationships between chronic life stressors, racial/ethnic identity, and odds of experiencing any chronic pain and high-impact chronic pain. Results indicate that in 2018, the most common chronic life stressor among middle-aged and older adults was dealing with their own health problems (68%), followed by dealing with the physical or emotional issues affecting a spouse or child (46%). Adjusted analyses showed that a higher total of chronic life stressors increased the odds of middle-aged and older adults experiencing any chronic pain and high-impact chronic pain. There were no significant interactions between the overall chronic life stress burden and racial/ethnic identity as a predictor of odds to experience any chronic pain or high-impact chronic pain, but significant interaction effects were found related to specific chronic life stressors. Findings underscore the significant impact of chronic life stressors on the chronic pain burden among middle-aged and older adults in the United States, which cut across racial/ethnic identity.

Florida-California Cancer Research, Education and Engagement (CaRE2) Health Equity Center: Structure, Innovations, and Initial Outcomes

INTRODUCTION

The Florida-California Cancer Research, Education, and Engagement (CaRE2) Health Equity Center is a triad partnership committed to increasing institutional capacity for cancer disparity research, the diversity of the cancer workforce, and community empowerment. This article provides an overview of the structure, process innovations, and initial outcomes from the first 4 years of the CaRE2 triad partnership.

METHODS

CaRE2 serves diverse populations in Florida and California using a "molecule to the community and back" model. We prioritize research on the complex intersection of biological, environmental, and social determinants health, working together with scientific and health disparities communities, sharing expertise across institutions, bidirectional training, and community outreach. Partnership progress and outcomes were assessed using mixed methods and four Program Steering Committee meetings.

RESULTS

Research capacity was increased through development of a Living Repository of 81 cancer model systems from minority patients for novel cancer drug development. CaRE2 funded 15 scientific projects resulting in 38 publications. Workforce diversity entailed supporting 94 cancer trainees (92 URM) and 34 ESIs (32 URM) who coauthored 313 CaRE2-related publications and received 48 grants. Community empowerment was promoted via outreaching to more than 3000 individuals, training 145 community cancer advocates (including 28 Community Scientist Advocates), and publishing 10 community reports. CaRE2 members and trainees together have published 639 articles, received 61 grants, and 57 awards.

CONCLUSION

The CaRE2 partnership has achieved its initial aims. Infrastructure for translational cancer research was expanded at one partner institution, and cancer disparities research was expanded at the two cancer centers.

Epigenetic Aging Mediates the Association between Pain Impact and Brain Aging in Middle to Older Age Individuals with Knee Pain

Chronic musculoskeletal pain is a health burden that may accelerate the aging process. Accelerated brain aging and epigenetic aging have separately been observed in those with chronic pain. However, it is unknown whether these biological markers of aging are associated with each other in those with chronic pain. We aimed to explore the association of epigenetic aging and brain aging in middle-to-older age individuals with varying degrees of knee pain. Participants (57.91 ± 8.04 y) with low impact knee pain (n = 95), high impact knee pain (n = 53), and pain-free controls (n = 26) completed self-reported pain, a blood draw, and an MRI scan. We used an epigenetic clock previously associated with knee pain (DNAmGrimAge), the subsequent difference of predicted epigenetic and brain age from chronological age (DNAmGrimAge-Difference and Brain-PAD, respectively). There was a significant main effect for pain impact group (F (2,167) = 3.847, P = 0.023, r o t a t i o n a l   e n e r g y   =   1 / 2 I ω 2 = 0.038, ANCOVA) on Brain-PAD and DNAmGrimAge-difference (F (2,167) = 6.800, P = 0.001, I   =   m k 2 = 0.075, ANCOVA) after controlling for covariates. DNAmGrimAge-Difference and Brain-PAD were modestly correlated (r =0.198; P =0.010). Exploratory analysis revealed that DNAmGrimAge-difference mediated GCPS pain impact, GCPS pain severity, and pain-related disability scores on Brain-PAD. Based upon the current study findings, we suggest that pain could be a driver for accelerated brain aging via epigenome interactions.

Cross-Sectional Brain-Predicted Age Differences in Community-Dwelling Middle-Aged and Older Adults with High Impact Knee Pain

Purpose

Knee OA-related pain varies in impact across individuals and may relate to central nervous system alterations like accelerated brain aging processes. We previously reported that older adults with chronic musculoskeletal pain had a significantly greater brain-predicted age, compared to pain-free controls, indicating an "older" appearing brain. Yet this association is not well understood. This cross-sectional study examines brain-predicted age differences associated with chronic knee osteoarthritis pain, in a larger, more demographically diverse sample with consideration for pain's impact.

Patients and Methods

Participants (mean age = 57.8 ± 8.0 years) with/without knee OA-related pain were classified according to pain's impact on daily function (ie, impact): low-impact (n=111), and high-impact (n=60) pain, and pain-free controls (n=31). Participants completed demographic, pain, and psychosocial assessments, and T1-weighted magnetic resonance imaging. Brain-predicted age difference (brain-PAD) was compared across groups using analysis of covariance. Partial correlations examined associations of brain-PAD with pain and psychosocial variables.

Results

Individuals with high-impact chronic knee pain had significantly "older" brains for their age compared to individuals with low-impact knee pain (p < 0.05). Brain-PAD was also significantly associated with clinical pain, negative affect, passive coping, and pain catastrophizing (p's<0.05).

Conclusion

Our findings suggest that high impact chronic knee pain is associated with an older appearing brain on MRI. Future studies are needed to determine the impact of pain-related interference and pain management on somatosensory processing and brain aging biomarkers for high-risk populations and effective intervention strategies.

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.

Triad Multisystem Phenotype with High-risk for Developing Temporomandibular Disorders- Characteristics and Potential Pathophysiology Results from the OPPERA Dataset

ABSTRACT

A multisystem phenotype with the Triad of bodily pain, psychological distress, and sleep disturbance was found to have high risk for developing initial onset of painful temporomandibular disorders (TMDs) in the multicenter Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) dataset. In this study, we systemically examined phenotypic characteristics and explored potential pathophysiology in quantitative sensory testing (QST) and autonomic nervous system (ANS) domains in this multisystem Triad phenotype. Secondary analysis was performed on 1199 non-Triad and 154 Triad TMD-free OPPERA enrollees at baseline. Results indicate that prior to developing TMDs, the Triad phenotype demonstrated both orofacial and systemic signs and symptoms that can only be captured through multisystem assessment. In addition, we found significantly lower resting heart rate variability and higher resting heart rate in the Triad phenotype as compared to the non-Triad group. However, pain sensitivity measured by QST was not different between groups. These findings highlight the importance of whole-person multisystem assessment at the stage prior to developing complex pain conditions such as TMDs, and suggest that, in addition to a "tissue damage monitor", pain should be considered in a broader context, such as a component within a "distress monitoring system" at the whole-person level when multisystem issues co-present. Therefore, the presence or absence of multisystem issues may carry critical information when searching for disease mechanisms and developing mechanism-based intervention and prevention strategies for TMDs and related pain conditions. Cardiovascular autonomic function should be further researched when multisystem issues co-present prior to developing TMDs.