Catechol-O-methyltransferase gene polymorphism and chronic human pain: a systematic review and meta-analysis

Investigating the Association between Catechol-O-Methyltransferase Gene Activity and Pain Perception in South African Patients with Different Temporomandibular Disorders Diagnoses

Background: Temporomandibular disorders (TMD) affect a significant portion of the population, with profound psychological, behavioral, and social repercussions. Recent investigations have explored the genetic basis underlying pain perception in individuals with TMD, aiming to elucidate the role of specific genetic factors in modulating the condition. Notably, genetic variations have been implicated in the pathogenesis of TMD, particularly genes involved in pain perception pathways. One of the primary candidates is the Catechol-O-Methyltransferase (COMT) gene, which plays a crucial role in the catecholaminergic system and has been associated with the regulation of nociceptive processes. This study seeks to investigate the correlation between COMT gene activity and pain perception among South African patients diagnosed with varying forms of TMD. Methodology: In this study, a total of 196 participants were enrolled, comprising 97 patients diagnosed with TMD and 99 control participants. The control group was meticulously matched with the TMD group for age, gender, and ethnicity. Data collection involved clinical and radiological investigations, and saliva sampling. The English version of the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) Axis I was utilized to evaluate all TMD participants, focusing on standard diagnostic measures based on clinical signs and symptoms of TMD, which primarily describe common physical manifestations of the disorder. Genomic DNA was extracted from saliva samples, enabling the analysis of single-nucleotide polymorphisms (SNPs) in the COMT gene, specifically targeting polymorphisms rs165774, rs9332377, rs6269, rs4646310, rs165656, and rs4680. Results: The current study demonstrated a pronounced gender disparity, with 80.41% of the participants being female and 19.59% male, suggesting that women in South Africa either exhibit a higher susceptibility to TMD or are more likely to seek treatment for the condition compared to men. The highest prevalence of TMD was observed in the white population (58.76%). Additionally, over 65% of TMD patients were diagnosed with at least two Axis I diagnoses, a figure that increased to 89% for those diagnosed with three Axis I diagnoses. The findings further indicated significant associations between several single-nucleotide polymorphisms (SNPs) in the Catechol-O-Methyltransferase (COMT) gene-specifically rs165656, rs9332377, rs4646310, rs6269, and rs165774-and both TMD and TMD-related pain. Myofascial pain with referral and myalgia showed a strong association with the COMT SNPs rs9332377 and rs4646310. Furthermore, COMT SNP rs4646310 was also associated with disability related to TMD. Conclusions: This study substantiates the hypothesis that pain is prevalent in a considerable proportion of patients affected by TMD. Furthermore, the findings reveal a significant association between COMT gene activity and pain perception in South African patients diagnosed with TMD.

Genetic influence on treatment outcomes in patients with pain-related temporomandibular disorders

BACKGROUND

Single nucleotide polymorphisms (SNPs) may influence pain susceptibility and impact treatment response in pain-related temporomandibular disorders (TMDp).

OBJECTIVE

Explore the role of COMT (rs4646310, rs6269, rs4818, rs4680) and OPRM1 (rs1799971) genotypes in regulating treatment response.

METHODS

Sixty TMDp patients (55 females and 5 males), diagnosed with the Diagnostic Criteria for TMD (DC/TMD), underwent standardised treatment (information and education, home physical therapy, occlusal splint) for 6 months. Treatment outcomes included: pain intensity, pain-free mouth opening, jaw functional limitation, depression, and anxiety. Genotyping for COMT and OPRM1 SNPs was performed using DNA from buccal mucosa swabs and TaqMan assays. Statistical analysis was carried out to compare the changes in treatment outcomes and the influence of genotypes on treatment response.

RESULTS

Significantly less pain reduction was observed in minor allele carriers of rs4646310, and rs4680 compared to dominant homozygous (p < .025). Minor allele carriers of rs1799971 and rs4646310 demonstrated worsening in pain-free mouth opening while dominant homozygous exhibited improvement (p < .025). Significantly less anxiety reduction was observed in minor allele carriers of rs4646310 compared to dominant homozygous (p = .003). Of the all variables assessed in the regression model, carrying a minor allele of rs1799971 predicted a poorer treatment response considering pain-free mouth opening while carrying a minor allele of rs4646310 predicted less pain and less anxiety reduction.

CONCLUSION

Our findings indicate that certain SNP variants of the COMT and OPRM1 genes were associated with poorer treatment response and may therefore play a significant role in the classification of TMDp patients. Also, assessment of patient genotype could potentially aid in predicting treatment response.

Association of OPRM1 rs1799971, HTR1B rs6296 and COMT rs4680 polymorphisms with clinical phenotype among women with fibromyalgia

To investigate the association between three selected pain polymorphisms and clinical, functional, sensory-related, psychophysical, psychological or cognitive variables in a sample of women with fibromyalgia (FMS). One hundred twenty-three (n = 123) women with FMS completed demographic (age, height, weight), clinical (years with pain, intensity of pain at rest and during daily living activities), functional (quality of life, physical function), sensory-related (sensitization-associated and neuropathic-associated symptoms), psychophysical (pressure pain thresholds), psychological (sleep quality, depressive and anxiety level) and cognitive (pain catastrophizing, kinesiophobia) variables. Those three genotypes of the OPRM1 rs1799971, HTR1B rs6296 and COMT rs4680 single nucleotide polymorphisms were obtained by polymerase chain reactions from no-stimulated whole saliva collection. No significant differences in demographic, clinical, functional, sensory-related, psychophysical, psychological and cognitive variables according to OPRM1 rs1799971, HTR1B rs6296 or COMT rs4680 genotype were identified in our sample of women with FMS. A multilevel analysis did not either reveal any significant gene-to-gene interaction between OPRM1 rs1799971 x HTR1B rs6296, OPRM1 rs1799971 x COMT rs4680 and HTR1B rs6296 x COMT rs4680 for any of the investigated outcomes. This study revealed that three single nucleotide polymorphisms, OPRM1 rs1799971, HTR1B rs6296 or COMT rs4680, mostly associated with chronic pain were not involved in phenotyping features of FMS. Potential gene-to-gene interaction and their association with clinical phenotype in women with FMS should be further investigated in future studies including large sample sizes.

Characteristics associated with response to subcutaneously administered anti-CGRP monoclonal antibody medications in a real-world community cohort of persons living with migraine: A retrospective clinical and genetic study

OBJECTIVE

To evaluate response to anti-calcitonin gene-related peptide (CGRP) migraine preventives in a real-world community cohort of persons living with migraine and to identify clinical and genetic characteristics associated with efficacious response.

BACKGROUND

Erenumab-aooeb, fremanezumab-vrfm, and galcanezumab-gnlm target CGRP or its receptor; however, many patients are non-responsive.

METHODS

In this retrospective clinical and genetic study, we identified 1077 adult patients who satisfied the International Classification of Headache Disorders, 3rd edition, criteria for migraine without aura, migraine with aura, or chronic migraine and who were prescribed an anti-CGRP migraine preventive between May 2018 and May 2021. Screening of 558 patients identified 289 with data at baseline and first follow-up visits; data were available for 161 patients at a second follow-up visit. The primary outcome was migraine days per month (MDM). In 198 genotyped patients, we evaluated associations between responders (i.e., patients with ≥50% reduction in MDM at follow-up) and genes involved in CGRP signaling or pharmacological response, and genetic and polygenic risk scores.

RESULTS

The median time to first follow-up was 4.4 (0.9-22) months after preventive start. At the second follow-up, 5.7 (0.9-13) months later, 145 patients had continued on the same preventive. Preventives had strong, persistent effects in reducing MDM in responders (follow-up 1: η2  = 0.26, follow-up 2: η2  = 0.22). At the first but not second follow-up: galcanezumab had a larger effect than erenumab, while no difference was seen at either follow-up between galcanezumab and fremanezumab or fremanezumab and erenumab. The decrease in MDM at follow-up was generally proportional to baseline MDM, larger in females, and increased with months on medication. At the first follow-up only, patients with prior hospitalization for migraine or who had not responded to more preventive regimens had a smaller decrease in MDM. Reasons for stopping or switching a preventive varied between medications and were often related to cost and insurance coverage. At both follow-ups, patient tolerance (1: 92.2% [262/284]; 2: 95.2% [141/145]) and continued use (1: 77.5% [224/289]; 2: 80.6% [116/145]) were high and similar across preventives. Response consistency (always non-responders: 31.7% [46/145]; always responders: 56.5% [82/145], and one-time only responders: 11.7% [17/145]) was also similar across preventives. Non-responder status had nominally significant associations with rs12615320-G in RAMP1 (odds ratio [95% confidence interval]: 4.7 [1.5, 14.7]), and rs4680-A in COMT (0.6[0.4, 0.9]). Non-responders had a lower mean genetic risk score than responders (1.0 vs. 1.1; t(df) = -1.75(174.84), p = 0.041), and the fraction of responders increased with genetic and polygenic risk score percentile.

CONCLUSIONS

In this real-world setting, anti-CGRP preventives reduced MDM persistently and had similar and large effect sizes on MDM reduction; however, clinical and genetic factors influenced response.

Unraveling Catechol-O-Methyltransferase rs4680 SNP's Role in Patients' Response to Tramadol and Its Adverse Effects: A Pharmacogenetics Insight into Postoperative Pain Management

Effective postoperative pain management is essential for patient well-being and an efficient healthcare system. Variations in the Catechol O-Methyltransferase (COMT) gene, specifically rs4680, play a crucial role in pain perception and opioid response. This study seeks to elucidate the impact of rs4680 polymorphism on tramadol efficacy and adverse reactions in post-surgical patients. We performed an uncontrolled cohort pharmacogenetics study in which participants underwent postoperative tramadol administration. The frequencies of rs4680 alleles were determined and the association between rs4680 genotypes and the efficacy of tramadol analgesic as pain relief, measured by the Numeric Rating Scale (NRS), was analyzed. Secondary outcomes included tramadol-induced sedation levels, opioid-induced nausea and vomiting, and other adverse effects of tramadol. Data analysis, using IBM SPSS Statistics 23, focused on pain and side effect differences across genotypes, with statistical significance set to p ≤ 0.05. The COMT (rs4680) genotype distribution exhibited a 'G' allele frequency of 41.5% and an 'A' allele frequency of 58.5%, with the AA genotype present in 44% of individuals, adhering to the Hardy-Weinberg equilibrium (p = 0.788). Patients with the AA genotype reported lower pain scores post-tramadol administration across all times examined (p < 0.001), but also experienced statistically significant (p < 0.001) higher incidences of tramadol-induced nausea, vomiting, and sedation. However, GG genotype individuals experienced poor pain relief from tramadol, requiring more supplemental analgesia. These significant findings underscore the critical role of COMT rs4680 polymorphism in response to tramadol and the necessity of a personalized approach to postoperative pain management.

Association of Genetic Variants with Postsurgical Pain: A Systematic Review and Meta-analyses

BACKGROUND

Postsurgical pain is a key component of surgical recovery. However, the genetic drivers of postsurgical pain remain unclear. A broad review and meta-analyses of variants of interest will help investigators understand the potential effects of genetic variation.

METHODS

This article is a systematic review of genetic variants associated with postsurgical pain in humans, assessing association with postsurgical pain scores and opioid use in both acute (0 to 48 h postoperatively) and chronic (at least 3 months postoperatively) settings. PubMed, Embase, and the Cochrane Central Register of Controlled Trials were searched from 2000 to 2022 for studies using search terms related to genetic variants and postsurgical pain in humans. English-language studies in adult patients examining associations of one or more genetic variants with postsurgical pain were included. The primary outcome was association of genetic variants with either acute or chronic postsurgical pain. Pain was measured by patient-reported pain score or analgesic or opioid consumption.

RESULTS

A total of 163 studies were included, evaluating 129 unique genes and 594 unique genetic variants. Many of the reported significant associations fail to be replicated in other studies. Meta-analyses were performed for seven variants for which there was sufficient data (OPRM1 rs1799971; COMT rs4680, rs4818, rs4633, and rs6269; and ABCB1 rs1045642 and rs2032582). Only two variants were associated with small differences in postsurgical pain: OPRM1 rs1799971 (for acute postsurgical opioid use standard mean difference = 0.25; 95% CI, 0.16 to 0.35; cohort size, 8,227; acute postsurgical pain score standard mean difference = 0.20; 95% CI, 0.09 to 0.31; cohort size, 4,619) and COMT rs4680 (chronic postsurgical pain score standard mean difference = 0.26; 95% CI, 0.08 to 0.44; cohort size, 1,726).

CONCLUSIONS

Despite much published data, only two alleles have a small association with postsurgical pain. Small sample sizes, potential confounding variables, and inconsistent findings underscore the need to examine larger cohorts with consistent outcome measures.

EDITOR’S PERSPECTIVE

Precision management of post-COVID pain: An evidence and clinical-based approach

Background Pain after a SARS-CoV-2 acute infection (post-COVID pain) is becoming a new healthcare emergency but remains underestimated and most likely undertreated due to a lack of recognition of the phenomenon and knowledge of the underlying pain mechanisms. Evidence supporting any particular treatment approach for the management of post-COVID pain is lacking. Large variability in the patient response to any standard pain treatments is clinically observed, which has led to calls for a personalized, tailored approach to treating patients with chronic post-COVID pain (i.e. 'precision pain medicine'). Applying the global concerted action towards precision medicine to post-COVID pain could help guide clinical decision-making and aid in more effective treatments. Methods The current position paper discusses factors to be considered by clinicians for managing post-COVID pain ranging from identification of the pain phenotype to genetic consideration. Results The ability of clinicians to phenotype post-COVID pain into nociceptive, neuropathic, nociplastic or mixed type is suggested as the first step to better planification of a treatment programme. Further, the consideration of other factors, such as gender, comorbidities, treatments received at the acute phase of infection for onset-associated COVID-19 symptoms, factors during hospitalization or the presence of emotional disturbances should be implemented into a treatment programme. Conclusions Accordingly, considering these factors, management of post-COVID pain should include multimodal pharmacological and non-pharmacological modalities targeting emotional/cognitive aspects (i.e. psychological and/or coping strategies), central sensitization-associated mechanisms (i.e. pain neuroscience education), exercise programmes as well as lifestyle interventions (e.g. nutritional support and sleep management). SIGNIFICANCE: This position paper presents an evidence-based clinical reasoning approach for precision management of post-COVID pain.

COMT Val158Met Affects the Analgesic Response to Acupuncture Among Cancer Survivors With Chronic Pain

Catechol-O-methyltransferase (COMT) is the major enzyme involved in the catabolism of dopamine, a neurotransmitter in the brain's reward system. The common COMT polymorphism Val158Met (rs4680 G>A) modulates pain response to opioids through a reward-motivated mechanism; however, its role in nonpharmacological pain medicine has not been clinically characterized. We genotyped 325 participants from a randomized controlled trial of cancer survivors with chronic musculoskeletal pain. We found that carrying methionine at position 158 (158Met) of COMT, encoded by the A allele, significantly increased the analgesic response to electroacupuncture (74% vs 50%; odds ratio [OR]: 2.79; 95% confidence interval [CI]: 1.31, 6.05; P < .01), but not to auricular acupuncture (68% vs 60%; OR: 1.43; 95% CI: .65, 3.12; P = .37) or usual care (24% vs 18%; OR: 1.46; 95% CI: .38, 7.24; P = .61) compared to Val/Val. These findings raise the possibility that COMT Val158Met might be an important predictor of analgesic response to electroacupuncture, providing novel insights into precision nonpharmacologic pain management tailored to individual genetic backgrounds. PERSPECTIVE: This work suggests the modulating effects of the polymorphism in COMT Val158Met on the response to acupuncture. Further research needs to validate these findings, increase the mechanistic understanding of acupuncture, and guide further development of acupuncture as a precision pain management strategy.

Pain Biomarkers in Fibromyalgia Syndrome: Current Understanding and Future Directions

Fibromyalgia is a complex and heterogeneous clinical syndrome, mainly characterized by the presence of widespread pain, possibly associated with a variety of other symptoms. Fibromyalgia can have an extremely negative impact on the psychological, physical and social lives of people affected, sometimes causing patients to experience dramatically impaired quality of life. Nowadays, the diagnosis of fibromyalgia is still clinical, thus favoring diagnostic uncertainties and making its clear identification challenging to establish, especially in primary care centers. These difficulties lead patients to undergo innumerable clinical visits, investigations and specialist consultations, thus increasing their stress, frustration and even dissatisfaction. Unfortunately, research over the last 25 years regarding a specific biomarker for the diagnosis of fibromyalgia has been fruitless. The discovery of a reliable biomarker for fibromyalgia syndrome would be a critical step towards the early identification of this condition, not only reducing patient healthcare utilization and diagnostic test execution but also providing early intervention with guideline-based treatments. This narrative article reviews different metabolite alterations proposed as possible biomarkers for fibromyalgia, focusing on their associations with clinical evidence of pain, and highlights some new, promising areas of research in this context. Nevertheless, none of the analyzed metabolites emerge as sufficiently reliable to be validated as a diagnostic biomarker. Given the complexity of this syndrome, in the future, a panel of biomarkers, including subtype-specific biomarkers, could be considered as an interesting alternative research area.

The Role of Female Reproductive Hormones in the Association between Migraine and Breast Cancer: An Unanswered Question

Accumulating epidemiological studies have investigated a possible interconnection between migraine (Mi) and breast cancer (BC) because of the strong link between these diseases and female reproductive hormones. This review aims to consolidate findings from epidemiological studies and explore biologically plausible hypothetical mechanisms related to hormonal pathways. Current evidence suggests a protective role of Mi in BC development, particularly in case-control studies but not in cohort ones. The inconsistency among studies may be due to several reasons, including diagnostic criteria for Mi and the age gap between the development of these two diseases. Furthermore, recent research has challenged the concept of a net beneficial effect of Mi on BC, suggesting a more complex relationship between the two conditions. Many polymorphisms/mutations in hormone-related pathways are involved in at least one of the two conditions. The most promising evidence has emerged for a specific alteration in the estrogen receptor 1 gene (rs2228480). However, the possible specific mutation or polymorphism involved in this association has not yet been identified. Further studies with robust methodologies are needed to validate the protective role of Mi in BC and fully elucidate the precise nature of this causal relationship.

Sex Differences in Opioid Response Linked to OPRM1 and COMT genes DNA Methylation/Genotypes Changes in Patients with Chronic Pain

Analgesic-response variability in chronic noncancer pain (CNCP) has been reported due to several biological and environmental factors. This study was undertaken to explore sex differences linked to OPRM1 and COMT DNA methylation changes and genetic variants in analgesic response. A retrospective study with 250 real-world CNCP outpatients was performed in which data from demographic, clinical, and pharmacological variables were collected. DNA methylation levels (CpG island) were evaluated by pyrosequencing, and their interaction with the OPRM1 (A118G) and COMT (G472A) gene polymorphisms was studied. A priori-planned statistical analyses were conducted to compare responses between females and males. Sex-differential OPRM1 DNA methylation was observed to be linked to lower opioid use disorder (OUD) cases for females (p = 0.006). Patients with lower OPRM1 DNA methylation and the presence of the mutant G-allele reduced opioid dose requirements (p = 0.001), equal for both sexes. Moreover, COMT DNA methylation levels were negatively related to pain relief (p = 0.020), quality of life (p = 0.046), and some adverse events (probability > 90%) such as constipation, insomnia, or nervousness. Females were, significantly, 5 years older with high anxiety levels and a different side-effects distribution than males. The analyses demonstrated significant differences between females and males related to OPRM1 signalling efficiency and OUD, with a genetic-epigenetic interaction in opioid requirements. These findings support the importance of sex as a biological variable to be factored into chronic pain-management studies.

Evidence Regarding Pharmacogenetics in Pain Management and Cancer

Patients experience interindividual variation in response to analgesics, which may be partially explained by genetics. This commentary discusses a recently published trial on COMT genotype and opioid dose requirements and describes the potential role for COMT and other genes (eg, CYP2D6) on opioid therapy and the current evidence for germline pharmacogenetics and resources for opioid pharmacogenetics.

The Biology of Stress Intolerance in Patients with Chronic Pain—State of the Art and Future Directions

Stress has been consistently linked to negative impacts on physical and mental health. More specifically, patients with chronic pain experience stress intolerance, which is an exacerbation or occurrence of symptoms in response to any type of stress. The pathophysiological mechanisms underlying this phenomenon remain unsolved. In this state-of-the-art paper, we summarised the role of the autonomic nervous system (ANS) and hypothalamus-pituitary-adrenal (HPA) axis, the two major stress response systems in stress intolerance. We provided insights into such mechanisms based on evidence from clinical studies in both patients with chronic pain, showing dysregulated stress systems, and healthy controls supported by preclinical studies, highlighting the link between these systems and symptoms of stress intolerance. Furthermore, we explored the possible regulating role for (epi)genetic mechanisms influencing the ANS and HPA axis. The link between stress and chronic pain has become an important area of research as it has the potential to inform the development of interventions to improve the quality of life for individuals living with chronic pain. As stress has become a prevalent concern in modern society, understanding the connection between stress, HPA axis, ANS, and chronic health conditions such as chronic pain is crucial to improve public health and well-being.

Are catechol-O-methyltransferase gene polymorphisms genetic markers for pain sensitivity after all? - A review and meta-analysis

The catechol-O-methyltransferase (COMT) gene has arguably been the designated pain sensitivity gene for nearly two decades. However, the literature provides inconsistent evidence. We performed several meta-analyses including k = 31 samples and n = 4631 participants thereby revealing small effects of rs4680 on pain thresholds in fibromyalgia, headache and across chronic pain conditions. Moreover, rs4680 effects were found across pain patients when affected, but not unaffected, body sites were assessed. No effect was detected for any other SNP investigated. Importantly, our results corroborate earlier findings in that we found a small effect of COMT haplotypes on pain sensitivity. Our review and meta-analysis contribute to the understanding of COMT-dependent effects on pain perception, provide insights into research issues and offer future directions. The results support the theory that rs4680 might only impact behavioural measures of pain when descending pain modulatory pathways are sufficiently challenged. After all, COMT polymorphisms are genetic markers of pain sensitivity, albeit with some limitations which are discussed with respect to their implications for research and clinical significance.

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.

Multidimensional evaluation of the pain profile as prognostic factor in individuals with hip or knee osteoarthritis receiving total joint replacement: protocol of a 2-year longitudinal prognostic cohort study

INTRODUCTION

Knee and hip osteoarthritis are two highly prevalent musculoskeletal pain conditions. Unsuccessful rates after hip/knee replacement range from 10% to 20%. Subjects with sensitisation manifestations are vulnerable to worse clinical outcomes. Most studies have analysed outcomes up to 1 year after surgery. The aim of this 2-year longitudinal study will be to evaluate sensory-related, psychological and psychophysical pain sensitisation manifestations and a potential epigenetic biomarker as prognostic clinical outcomes for the development of chronic postoperative pain after knee or hip replacement.

METHODS AND ANALYSIS

A prospective longitudinal study with a 2-year follow-up period will be conducted. The prognostic variables will include pain, function, related-disability, anxiety, depression, quality of life, sensitisation-associated symptoms, kinesiophobia, neuropathic pain and catastrophising, and expectative of the intervention will be assessed before surgery. We will also evaluate the presence of the Val158Met polymorphism as a possible epigenetic marker. Clinical outcomes including pain, related-disability and self-perceived satisfaction, sensitisation-associated symptoms and neuropathic pain will be assessed 3, 6, 12, 18 and 24 months after surgery. These variables will be used to construct three prediction models: (1) pain and function, (2) sensitisation-associated symptomatology and (3) neuropathic pain features classifying those patients in responders and non-responders. Data from knee or hip osteoarthritis will be analysed separately. Statistical analyses will be conducted with logistic regressions.

ETHICS AND DISSEMINATION

The study has been approved by the Ethics Committee of both institutions involved (Hospital Universitario Fundación Alcorcón (HUFA) 19-141 and Universidad Rey Juan Carlos (URJC) 0312201917319). Participants will sign the written informed consent before their inclusion. Study results will be disseminated through peer-reviewed publications and presentations at scientific meetings.

Working memory dysfunction in fibromyalgia is associated with genotypes of the catechol- O-methyltransferase gene: an event-related potential study

Recent findings have associated different COMT genotypes with working memory capacity in patients with fibromyalgia. Although it is thought that the COMT gene may influence neural correlates (P2 and P3 ERP components) underlying working memory impairment in this chronic-pain syndrome, it has not yet been explored. Therefore, the aim of the present research was to investigate the potential effect of the COMT gene in fibromyalgia patients on ERP working memory indices (P2 and P3 components). For this purpose, 102 participants (51 patients and 51 healthy control participants) took part in the experiment. Event-related potentials and behavioral responses were recorded while participants performed a spatial n-back task. Participants had to decide if the stimulus coincided or not in the same location as the one presented one (1-back condition) or two (2-back condition) trials before. Genotypes of the COMT gene were determined through a saliva sample from all participants. Present results significantly showed lower working memory performance (p < 0.05) in patients with fibromyalgia as compared to control participants (higher rate of errors and slower reaction times). At neural level, we found that patients exhibited enhanced frontocentral and parieto-occipital P2 amplitudes compared to control participants (p < 0.05). Interestingly, we also observed that only fibromyalgia patients carrying the Val/Val genotype of the COMT gene showed higher frontocentral P2 amplitudes than control participants (p < 0.05). Current results (behavioral outcomes and P2 amplitudes) confirmed the presence of an alteration in working memory functioning in fibromyalgia. The enhancement of frontocentral P2 could be reflecting that these patients would manifest an inefficient way of activating executive attention processes, in carriers of the Val/Val genotype of COMT. To our knowledge, the present findings are the first linking neural indices of working memory dysfunctions and COMT genotypes in fibromyalgia. Applying a subgroup of patient's strategy based on this genetic marker could be useful to establish more tailored therapeutical approaches.

Genetic overlap between temporomandibular disorders and primary headaches: A systematic review

Primary headache disorders (PHD), specifically migraine, are strongly associated with temporomandibular disorders (TMD), sharing some patterns of orofacial pain. Both disorders have significant genetic contributions already studied. PRISMA guidelines were followed to conduct this systematic review, which comprehensively summarize and discuss the genetic overlap between TMD and PHD to aid future research in potential therapy targets. This review included eight original articles published between 2015 and 2020, written in English and related to either TMD and/or PHD. The genes simultaneously assessed in PHD and TMD studies were COMT, MTHFR, and ESR1. COMT was proved to play a critical role in TMD pathogenesis, as all studies have concluded about its impact on the occurrence of the disease, although no association with PHD was found. No proof on the impact of MTHFR gene regulation on either TMD or PHD was found. The most robust results are concerning the ESR1 gene, which is present in the genetic profile of both clinical conditions. This novel systematic review highlights not only the need for a clear understanding of the role of ESR1 and COMT genes in pain pathogenesis, but it also evaluates their potential as a promising therapeutic target to treat both pathologies.

Are Pain Polymorphisms Associated with the Risk and Phenotype of Post-COVID Pain in Previously Hospitalized COVID-19 Survivors?

Objective: To investigate the association of different, selected pain polymorphisms with the presence of de novo long-COVID pain symptoms and to analyze the association between these polymorphisms with clinical, sensory-related, cognitive and psychological variables in COVID-19 survivors. Methods: Two hundred and ninety-three (n = 293, 49.5% female, mean age: 55.6 ± 12.9 years) previously hospitalized COVID-19 survivors participated. Three genotypes of the following single nucleotide polymorphisms (SNPs) were obtained from non-stimulated saliva: OPRM1 (rs1799971), COMT (rs4680), BDNF (rs6265), and HTR1B (rs6296) by polymerase chain reactions in all participants. Further, clinical (intensity/duration of pain), sensory-related (sensitization-associated symptoms, neuropathic pain features), psychological (anxiety or depressive levels, sleep quality), and cognitive (catastrophizing, kinesiophobia) variables were collected in those COVID-19 survivors suffering from post-COVID pain. Analyses were carried out to associate clinical features with genotype. Results: Participants were assessed 17.8 ± 5.2 months after hospitalization. One hundred and seventeen (39.9%) experienced post-COVID pain (particularly of musculoskeletal origin). The distributions of the genotype variants of any SNP were not significantly different between COVID-19 survivors with and without long-term post-COVID pain (all, p > 0.178). No differences in sensitization-associated symptoms, neuropathic pain features, catastrophizing, kinesiophobia levels, anxiety and depressive levels or sleep quality according to the genotype variant in any SNPs were found. No effect of gender was identified. Conclusion: The four SNPs generally associated with pain did not appear to predispose to the development of de novo long-COVID pain symptoms in previously hospitalized COVID-19 survivors. The SNPs were not involved in the phenotypic features of post-COVID pain either.

Comparative study of the efficacy of dexmedetomidine and fentanyl on anxiety and pain of parturients with different COMTva1158met genotypes

Objective

This study investigates the effects of COMTval158met gene polymorphism on maternal anxiety and pain during delivery and on the analgesic and anxiety efficacy of dexmedetomidine during delivery.

Methods

Sixty-one pregnant women, who were hospitalized in our hospital from January to November of 2016 were recruited and randomly divided into two groups, F and D groups. The pregnant women in the F group were given labor analgesia with ropivacaine combined with fentanyl. The pregnant women in the D group were given labor analgesia with ropivacaine combined with dexmedetomidine. Before and after labor analgesia, the genotype of COMT in the blood from two groups was detected, and the situation of labor anxiety and analgesia was analyzed. Then, the relationship between labor anxiety, analgesia, and COMT polymorphism was analyzed.

Results

In the 61 pregnant women, there were 30 women of wild homozygotes (GG) of COMT, 22 women of mutant heterozygotes (GA), and nine women of mutant homozygotes (AA), the mutation rate of allele A was 23.77%. The anxiety status score, anxiety trait score, and pain score in the AA genotype were significantly higher than those in the GG and GA genotype (p < 0.05). There was a significant difference in the efficacy of GG and AA genotypes between groups D and F for treating labor anxiety (p < 0.05), the efficacy of group D was better than that of group F in treating delivery anxiety, there was no significant difference in anxiety scores between the two groups in GA genotypes (p > 0.05); there was no significant difference in pain between group D and F in GG, GA, and AA genotypes (p > 0.05). There was no significant difference in pain and anxiety scores between the three genotypes in group D (p > 0.05), there was significant difference in pain scores among the three genotypes in group F (p < 0.05), but there was no significant difference in anxiety (p > 0.05).

Conclusions

The mutation of the COMTval158met gene leads to increased anxiety and pain during childbirth. The effect of dexmedetomidine on the anxiety of GG and AA genotypes is better than that of fentanyl, and the mutation of the COMTval158met gene has no impact on dexmedetomidine effect.

Polymorphisms in the HTR2A and HTR3A Genes Contribute to Pain in TMD Myalgia

Background: The aim of this study was to investigate if single nucleotide polymorphisms (SNPs) related to monoaminergic neurotransmission, in particular the serotonergic pathway, contribute to pain perception in patients with temporomandibular disorder (TMD) myalgia and if there is a correlation to jaw function as well as psychosocial factors such as stress, anxiety and depression.

Materials and Methods: One hundred and seventeen individuals with TMD myalgia were included. A venous blood or saliva sample was taken for genetic analyses and genotyped regarding HTR2A (rs9316233) HTR3A (rs1062613), HTR3B (rs1176744), SERT (5-HTTLPR) and COMT (rs4680). A clinical examination according to Diagnostic Criteria for TMD (DC/TMD) was performed and axis II data (psychosocial factors) were compared between participants with different genotypes for each gene using Kruskall–Wallis test. The characteristic pain intensity (CPI) was tested for correlations to scores for the Perceived Stress Scale, Generalized Anxiety Disorder, and Patient Health Questionnaires using Spearman's rank correlation test with Bonferroni correction for multiple testing. To further explore data factor analysis was performed to identify latent factors associated to the outcome variables.

Results: Participants carrying at least one copy of the rare allele of the HTR2A (rs9316233) and HTR3A (rs1062613) had higher CPI compared with the participants with the homozygous common genotype (P = 0.042 and P = 0.024, respectively). Correlation analyses showed several significant positive correlations between CPI on one hand, and self-reported psychosocial distress and jaw function on the other hand for several genotypes that mostly were weak to moderate. The factor analysis identified two latent variables. One was positively correlated to the HTR3B gene, jaw function and self-reported parafunctions, and the other was positively correlated to psychological distress and negatively correlated to SERT.

Conclusion: Taken together, the polymorphism rs1062613 in the HTR3A gene contributes to pain intensity in TMD myalgia. This together with positive interactions between pain variables and psychological factors in genotypes strengthens that pain and psychological distress are related. Further research is needed to explore this as well as the influence of gene-to-gene interactions on pain and psychological distress.

UNRAVELING THE CLINICO-GENETIC ASSOCIATION OF CATECHOL-O-METHYLTRANSFERASE-RS4680 G>A GENE POLYMORPHISM IN WOMEN WITH FIBROMYALGIA SYNDROME

OBJECTIVE

The aim: To determine the clinical and the genetic association of the COMT rs4680 SNP in women with FMS.

PATIENTS AND METHODS

Materials and methods: Extracted DNA from peripheral blood samples were utilized as template for the PCR and RFLP analysis.

RESULTS

Results: A significant difference was found in the distribution of the COMT genotype between FMS patients and controls (P<0.05). The frequency of GG, AG, AA genotypes were 12%, 72%, 21% in FMS patients and 32%, 62%, 11% in controls. The clinical features of FMS reveal that FIQR and the severity of pain measured by VAS were significantly associated with the COMT rs4680 SNP (P=0.042; P=0.016). The co-dominant model for GG verse v. AG genotype (P=0.004) and AG v. AA genotype (P=0.002) has shown to be high risk for FMS. An increased risk of FMS in the dominant model for (AG+AA) v. GG genotype (P=0.001) and no significant difference was found between (GG+AG) v. AA genotype (P=0.08) in the recessive model. The result indicated that A allele considerably increase the risk of FMS (P=0.004) in comparison to the G allele.

CONCLUSION

Conclusions: AA genotype and A allele of the COMT rs4680 SNP were significantly associated with severity in FMS patients and also plays a significant role in the clinical manifestation of this disease.

Genetics of menstrual migraine and their association with female hormonal factors

Perimenopause is linked to increased migraine (Mg), especially menstrual Mg (MMg), influenced by hormonal changes. Compared to nonmenstrual attacks, menstrual attacks are more disabling and less responsive to treatment. Women with perimenstrual estrogen withdrawal have been linked to Mg during menstruation, whereas Mg during perimenopause has been linked to unpredictable fluctuations in estrogen levels. It has been widely established that female sex hormones play a role in Mg, but how it occurs remains unclear. This narrative review was identified using Medline and PubMed searches between 1946 and 2021. Search terms included “headache,” “migraine,” “menstrual migraine,” “menstruation,” “menopause,” “perimenopause,” “estrogen,” and “progesterone.” This article focuses on the candidate genes and female hormones that play a role in MMg. More study is necessary to understand better the environmental components that play a critical role in disease development. Currently, there is insufficient clinical evidence to support the function of menstrual Mg. The specific research facts examined MMg unique candidate genes and female hormonal factors that support their association and found MMg etiologic processes for generating an early diagnostic marker.

Dopamine-neurotransmission and nociception in zebrafish: An anti-nociceptive role of dopamine receptor drd2a

Dopamine (DA) is an important modulator in nociception and analgesia. Spinal DA receptors are involved in descending modulation of the nociceptive transmission. Genetic variations within DA neurotransmission have been associated with altered pain sensitivity and development of chronic pain syndromes. The variant rs6277 in dopamine receptor 2 a (drd2a) has been associated with a decreased D₂ receptor availability and increased nociception. The aim of this study is to further characterize the role of DA neurotransmission in nociception and the anti-nociceptive function of drd2a. The phenotype caused by rs6277 was modelled in zebrafish larvae using morpholino's and the effect on nociception was tested using a validated behavioural assay. The anti-nociceptive role of drd2a was tested using pharmacological intervention of D₂ agonist Quinpirole. The experiments demonstrate that a decrease in drd2a expression results in a pro-nociceptive behavioural phenotype (P = 0.016) after a heat stimulus. Furthermore, agonism of drd2a with agonist Quinpirole (0.2 μM) results in dose-dependent anti-nociception (P = 0.035) after a heat stimulus. From these results it is concluded that the dopamine receptor drd2a is involved in anti-nociceptive behaviour in zebrafish. The model allows further screening and testing of genetic variation and treatment involved in nociception.

A novel rat model of temporomandibular disorder with improved face and construct validities

AIMS

Temporomandibular disorders are a cluster of orofacial conditions that are characterized by pain in the temporomandibular joint (TMJ) and surrounding muscles/tissues. Animal models of painful temporomandibular dysfunction (TMD) are valuable tools to investigate the mechanisms responsible for symptomatic temporomandibular joint and associated structures disorders. We tested the hypothesis that a predisposing and a precipitating factor are required to produce painful TMD in rats, using the ratgnawmeter, a device that determines temporomandibular pain based on the time taken for the rat to chew through two obstacles.

MATERIALS AND METHODS

Increased time in the ratgnawmeter correlated with nociceptive behaviors produced by TMJ injection of formalin (2.5%), confirming chewing time as an index of painful TMD. Rats exposed only to predisposing factors, carrageenan-induced TMJ inflammation or sustained inhibition of the catechol-O-methyltransferase (COMT) enzyme by OR-486, showed no changes in chewing time. However, when combined with a precipitating event, i.e., exaggerated mouth opening produced by daily 1-h jaw extension for 7 consecutive days, robust function impairment was produced.

KEY FINDINGS

These results validate the ratgnawmeter as an efficient method to evaluate functional TMD pain by evaluating chewing time, and this protocol as a model with face and construct validities to investigate symptomatic TMD mechanisms.

SIGNIFICANCE

This study suggests that a predisposition factor must be present in order for an insult to the temporomandibular system to produce painful dysfunction. The need for a combined contribution of these factors might explain why not all patients experiencing traumatic events, such as exaggerated mouth opening, develop TMDs.

Genetic variation in catechol-O-methyltransferase is associated with individual differences in conditioned pain modulation in healthy subjects

BACKGROUND

Genetic variation in the catechol-O-methyltransferase (COMT) gene is associated with sensitivity to both acute experimental pain and chronic pain conditions. Four single nucleotide polymorphisms (SNPs) have traditionally been used to infer three common haplotypes designated as low, average and high pain sensitivity and are reported to affect both COMT enzymatic activity and pain sensitivity. One mechanism that may partly explain individual differences in sensitivity to pain is conditioned pain modulation (CPM). We hypothesized that variation in CPM may have a genetic basis.

METHODS

We evaluated CPM in 77 healthy pain-free Caucasian subjects by applying repeated mechanical stimuli to the dominant forearm using 26-g von Frey filament as the test stimulus with immersion of the non-dominant hand in hot water as the conditioning stimulus. We assayed COMT SNP genotypes by the TaqMan method using DNA extracted from saliva.

RESULTS

SNP rs4680 (val¹⁵⁸ met) was not associated with individual differences in CPM. However, CPM was associated with COMT low pain sensitivity haplotypes under an additive model (p = 0.004) and the effect was independent of gender.

CONCLUSIONS

We show that, although four SNPs are used to infer COMT haplotypes, the low pain sensitivity haplotype is determined by SNP rs6269 (located in the 5' regulatory region of COMT), suggesting that inherited variation in gene expression may underlie individual differences in pain modulation. Analysis of 13 global populations revealed that the COMT low pain sensitivity haplotype varies in frequency from 13% to 44% and showed that two SNPs are sufficient to distinguish all COMT haplotypes in most populations.

Mechanism of Catechol-O-methyltransferase Regulating Orofacial Pain Induced by Tooth Movement

OBJECTIVE

To explore the mechanism of catechol-O-methyltransferase (COMT) in tooth movement pain.

METHODS

The experimental groups were randomly allocated into the healthy control, sham operation, model, model+shCOMT experimental, model+shCOMT control, and model+COMT antagonist groups. A tooth movement pain model was established. The pain stimulation and behavior test were performed. The duration of grooming behavior was determined. The appropriate experimental force and duration for application were selected. COMT shRNA vector was constructed and packaged as adenovirus. The shCOMT adenovirus was injected into the left infraorbital foramen. Seven days later, the trigeminal ganglia of all treatment groups were obtained. The COMT and IL-17 expressions were detected by western blot. The appropriate COMT antagonist concentration was selected. The pathological results of each group were detected by HE staining. The tooth movement distance was determined. The COMT gene expression was detected by FISH. The COMT and IL-17 expressions in the right trigeminal ganglion tissue of each group were detected by western blot.

RESULTS

The 60 g force and 14-day duration required the lowest stimulus intensity, the duration of grooming behavior was the longest, and the effect on COMT and IL-17 was the most significant. In the model group, formation of digestive cavity was seen in the trigeminal ganglion tissue, with infiltration of inflammatory cells, upregulation of the COMT and IL-17 expressions, and significant increase in the tooth movement distance. Compared with the model group, the shCOMT experimental group and the COMT antagonist group significantly improved the trigeminal ganglion tissue injury, significantly decreased the tooth movement distance, and significantly inhibited the COMT and IL-17 expressions.

CONCLUSION

The efficiency of tooth movement can be influenced by interfering the COMT-related gene expression. This proves that the COMT system can regulate the orthodontic tooth movement pain.

Contribution of CYP2D6 Functional Activity to Oxycodone Efficacy in Pain Management: Genetic Polymorphisms, Phenoconversion, and Tissue-Selective Metabolism

Oxycodone is a widely used opioid for the management of chronic pain. Analgesic effects observed following the administration of oxycodone are mediated mostly by agonistic effects on the μ-opioid receptor. Wide inter-subject variability observed in oxycodone efficacy could be explained by polymorphisms in the gene coding for the μ-opioid receptor (OPRM1). In humans, oxycodone is converted into several metabolites, particularly into oxymorphone, an active metabolite with potent μ-opioid receptor agonist activity. The CYP2D6 enzyme is principally responsible for the conversion of oxycodone to oxymorphone. The CYP2D6 gene is highly polymorphic with encoded protein activities, ranging from non-functioning to high-functioning enzymes. Several pharmacogenetic studies have shown the importance of CYP2D6-mediated conversion of oxycodone to oxymorphone for analgesic efficacy. Pharmacogenetic testing could optimize oxycodone therapy and help achieve adequate pain control, avoiding harmful side effects. However, the most recent Clinical Pharmacogenetics Implementation Consortium guidelines fell short of recommending pharmacogenomic testing for oxycodone treatment. In this review, we (1) analyze pharmacogenomic and drug-interaction studies to delineate the association between CYP2D6 activity and oxycodone efficacy, (2) review evidence from CYP3A4 drug-interaction studies to untangle the nature of oxycodone metabolism and its efficacy, (3) report on the current knowledge linking the efficacy of oxycodone to OPRM1 variants, and (4) discuss the potential role of CYP2D6 brain expression on the local formation of oxymorphone. In conclusion, we opine that pharmacogenetic testing, especially for CYP2D6 with considerations of phenoconversion due to concomitant drug administration, should be appraised to improve oxycodone efficacy.

Contribution of COMT and BDNF Genotype and Expression to the Risk of Transition From Acute to Chronic Low Back Pain

OBJECTIVES

A number of factors, including heritability and the environment, contribute to risk of transition from acute low back pain to chronic low back pain (CLBP). The aim of this study was to (1) compare somatosensory function and pain ratings at low back pain (LBP) onset between the acute low back pain and CLBP conditions and (2) evaluate associations between BDNF and COMT polymorphisms and expression levels at LBP onset to acute and chronic pain burden and risk for transition to the chronic pain state.

METHODS

In this longitudinal study, 220 participants were enrolled following recent onset of LBP and data were collected until the LBP resolved or until the end of the study at 6 months. Forty-two participants' pain resolved before 6 weeks from onset and 42 participants continued to have pain at 6 months. Patient-reported pain burden, somatosensory function (quantitative sensory testing), and blood samples were collected at each study visit.

RESULTS

CLBP is associated with greater pain burden and somatosensory hypersensitivity at the time of LBP onset. COMT rs4680 genotype (GG) was associated with acute cold pain sensitivity and with the risk for transition to CLBP while COMT expression was independently associated with risk for transition.

DISCUSSION

CLBP was characterized by higher reported pain burden and augmented hypersensitivity at LBP onset. COMT expression and genotype were associated with acute pain burden and likelihood of transition to CLBP.

A polygenic score for acute vaso-occlusive pain in pediatric sickle cell disease

Individuals with monogenic disorders can experience variable phenotypes that are influenced by genetic variation. To investigate this in sickle cell disease (SCD), we performed whole-genome sequencing (WGS) of 722 individuals with hemoglobin HbSS or HbSβ0-thalassemia from Baylor College of Medicine and from the St. Jude Children's Research Hospital Sickle Cell Clinical Research and Intervention Program (SCCRIP) longitudinal cohort study. We developed pipelines to identify genetic variants that modulate sickle hemoglobin polymerization in red blood cells and combined these with pain-associated variants to build a polygenic score (PGS) for acute vaso-occlusive pain (VOP). Overall, we interrogated the α-thalassemia deletion -α3.7 and 133 candidate single-nucleotide polymorphisms (SNPs) across 66 genes for associations with VOP in 327 SCCRIP participants followed longitudinally over 6 years. Twenty-one SNPs in 9 loci were associated with VOP, including 3 (BCL11A, MYB, and the β-like globin gene cluster) that regulate erythrocyte fetal hemoglobin (HbF) levels and 6 (COMT, TBC1D1, KCNJ6, FAAH, NR3C1, and IL1A) that were associated previously with various pain syndromes. An unweighted PGS integrating all 21 SNPs was associated with the VOP event rate (estimate, 0.35; standard error, 0.04; P = 5.9 × 10-14) and VOP event occurrence (estimate, 0.42; standard error, 0.06; P = 4.1 × 10-13). These associations were stronger than those of any single locus. Our findings provide insights into the genetic modulation of VOP in children with SCD. More generally, we demonstrate the utility of WGS for investigating genetic contributions to the variable expression of SCD-associated morbidities.

Genome-wide association study identifies RNF123 locus as associated with chronic widespread musculoskeletal pain

Background and objectives

Chronic widespread musculoskeletal pain (CWP) is a symptom of fibromyalgia and a complex trait with poorly understood pathogenesis. CWP is heritable (48%–54%), but its genetic architecture is unknown and candidate gene studies have produced inconsistent results. We conducted a genome-wide association study to get insight into the genetic background of CWP.

Methods

Northern Europeans from UK Biobank comprising 6914 cases reporting pain all over the body lasting >3 months and 242 929 controls were studied. Replication of three independent genome-wide significant single nucleotide polymorphisms was attempted in six independent European cohorts (n=43 080; cases=14 177). Genetic correlations with risk factors, tissue specificity and colocalisation were examined.

Results

Three genome-wide significant loci were identified (rs1491985, rs10490825, rs165599) residing within the genes Ring Finger Protein 123 (RNF123), ATPase secretory pathway Ca²⁺transporting 1 (ATP2C1) and catechol-O-methyltransferase (COMT). The RNF123 locus was replicated (meta-analysis p=0.0002), the ATP2C1 locus showed suggestive association (p=0.0227) and the COMT locus was not replicated. Partial genetic correlation between CWP and depressive symptoms, body mass index, age of first birth and years of schooling were identified. Tissue specificity and colocalisation analysis highlight the relevance of skeletal muscle in CWP.

Conclusions

We report a novel association of RNF123 locus and a suggestive association of ATP2C1 locus with CWP. Both loci are consistent with a role of calcium regulation in CWP. The association with COMT, one of the most studied genes in chronic pain field, was not confirmed in the replication analysis.

Fear of pain moderates the relationship between self-reported fatigue and methionine allele of catechol-O-methyltransferase gene in patients with fibromyalgia

Previous research has shown a consistent association among genetic factors, psychological symptoms and pain associated with fibromyalgia. However, how these symptoms interact to moderate genetic factors in fibromyalgia has rarely been studied to date. The present research investigates whether psychological symptoms can moderate the effects of catechol-O-methyltransferase on pain and fatigue. A total of 108 women diagnosed with fibromyalgia and 77 healthy control participants took part in the study. Pain, fatigue, and psychological symptoms (anxiety, depression, pain catastrophizing, fear of pain and fear of movement) were measured by self-report questionnaires. Two types of statistical analyses were performed; the first was undertaken to explore the influences of COMT genotypes on clinical symptoms by comparing patients with fibromyalgia and healthy controls. In the second analysis, moderation analyses to explore the role of psychological symptoms as potential factors that moderate the relationship between pain/fatigue and COMT genotypes were performed. The main results indicated that patients carrying the Met/Met genotype reported significantly higher levels of fatigue than heterozygote carriers (i.e., Met/Val genotype) and higher levels of fatigue, but not significantly different, than Val homozygote carriers. Among patients with fibromyalgia carrying methionine alleles (i.e., Met/Met + Met/Val carriers), only those who scored high on medical fear of pain, experienced an intensified feeling of fatigue. Thus, the present research suggests that fear of pain, as a psychological symptom frequently described in fibromyalgia may act as a moderating factor in the relationship between the Met allele of the COMT gene and the increase or decrease in self-reported fatigue. Although further research with wider patient samples is needed to confirm the present findings, these results point out that the use of psychological interventions focused on affective symptomatology might be a useful tool to reduce the severity of fibromyalgia.

A Pilot Study Investigating the Role of Gender in the Intergenerational Relationships between Gene Expression, Chronic Pain, and Adverse Childhood Experiences in a Clinical Sample of Youth with Chronic Pain

Chronic pain is a highly prevalent and costly issue that often emerges during childhood or adolescence and persists into adulthood. Adverse childhood experiences (ACEs) increase risk for several adverse health conditions, including chronic pain. Recent evidence suggests that parental trauma (ACEs, post-traumatic stress disorder (PTSD) symptoms) confers risk of poor health outcomes in their children. Intergenerational relationships between parental trauma and child chronic pain may be mediated by epigenetic mechanisms. A clinical sample of youth with chronic pain and their parents completed psychometrically sound questionnaires assessing ACEs, PTSD symptoms, and chronic pain, and provided a saliva sample. These were used to investigate the intergenerational relationships between four epigenetic biomarkers (COMT, DRD2, GR, and SERT), trauma, and chronic pain. The results indicated that the significant biomarkers were dependent upon the gender of the child, wherein parental ACEs significantly correlated with changes in DRD2 expression in female children and altered COMT expression in the parents of male children. Additionally, the nature of the ACE (maltreatment vs. household dysfunction) was associated with the specific epigenetic changes. There may be different pathways through which parental ACEs confer risk for poor outcomes for males and females, highlighting the importance of child gender in future investigations.

Discovery and characterization of naturally occurring potent inhibitors of catechol-O-methyltransferase from herbal medicines

Human catechol-O-methyltransferase (hCOMT) is considered a therapeutic target due to its crucial roles in the metabolic inactivation of endogenous neurotransmitters and xenobiotic drugs. There are nevertheless few safe and effective COMT inhibitors and there lacks a diversity in structure. To discover novel safe and effective hCOMT inhibitors from herbal products, in this study, 53 herbal products were collected and their inhibitory effects against hCOMT were investigated. Among them, Scutellariae radix (SR) displayed the most potent inhibitory effect on hCOMT with an IC50 value of 0.75 μg mL-1. To further determine specific chemicals as COMT inhibitors, an affinity ultrafiltration coupled with liquid chromatography-mass spectrometry method was developed and successfully applied to identify COMT inhibitors from SR extract. The results demonstrated that scutellarein 2, baicalein 9 and oroxylin A 12 were potent COMT inhibitors, showing a high binding index (>3) and very low IC50 values (32.9 ± 3.43 nM, 37.3 ± 4.32 nM and 18.3 ± 2.96 nM). The results of inhibition kinetics assays and docking simulations showed that compounds 2, 9 and 12 were potent competitive inhibitors against COMT-mediated 3-BTD methylation, and they could stably bind to the active site of COMT. These findings suggested that affinity ultrafiltration allows a rapid identification of natural COMT inhibitors from a complex plant extract matrix. Furthermore, scutellarein 2, baicalein 9 and oroxylin A 12 are potent inhibitors of hCOMT in SR, which could be used as promising lead compounds to develop more efficacious non-nitrocatechol COMT inhibitors for biomedical applications.

Fibromyalgia Pain and Depression: An Update on the Role of Repetitive Transcranial Magnetic Stimulation

Fibromyalgia is a musculoskeletal pain of different parts of the body, which is also associated with fatigue, lack of sleep, cognition deficits, family history, gender bias, and other disorders such as osteoarthritis and rheumatoid arthritis. It is generally initiated after trauma, surgery, infection, or stress. Fibromyalgia often coexists with several other conditions or disorders such as temporomandibular joint disorders, bowel and bladder syndrome, anxiety, depression, headaches, and interstitial cystitis. While there is no permanent cure for fibromyalgia, some interventions are available with multiple side effects. rTMS (repetitive transcranial magnetic stimulation), a noninvasive management strategy is used widely for various pain-related etiologies including fibromyalgia in both the laboratory and clinical settings. In this Review, we discuss the role and mechanism of action of rTMS in fibromyalgia patients and on associated comorbidities including anxiety, pain, depression, neurotransmitter alterations, sleep disorders, and overall quality of life of the patients suffering from this chronic problem. We also provide an update on the rTMS application in the clinical trials of fibromyalgia patients and prospective management therapy for multiple problems that these patients suffer.

Mutations and structural variations in Catechol-O-methyltransferase gene of patients exhibiting chronic persistent surgical pain

OBJECTIVES

Mutations in the exon 4 of the COMT gene are associated with chronic persistent surgical pain (CPSP). Especially COMT mutated allele G472A (Val158Met) associated with CPSP patients is reported in different ethnic population. The purpose of this study is to evaluate the prevalence of genetic mutations and structural variations in exon 4 of COMT that can be related to the appearance of CPSP in patients under sternotomy.

MATERIALS AND METHODS

One hundred patients with American Society of Anesthesiologists (ASA) physical status grades i, ii and iii, who underwent sternotomy procedures, were selected to assess the development and magnitude of the CPSP evaluated with pain questionaries' at the end of three months after surgery. This was correlated with COMT allele presence. The exon 4 of COMT gene (that contains the G472A allele) was studied. The polymerase chain reaction (PCR) products were sequenced and mutated sequences were deposited in GenBank®. The structural analysis of COMT was performed using ProCheck® and distortions of three-dimensional tertiary structural orientation was evaluated with root-mean-square deviation (RMSD) score.

RESULTS

Genetic analysis carried out through PCR showed 220 bp amplicons. The 25% of patients with CPSP showed a Numeric Rating Scale (NRS) > 4 pain score. The 20% of these patients have known Val158Met mutation, 5% of patients showed novel mutations c.382C>G, c.383G>C, p.(Arg128Ala). The mutations in COMT gene contributed major structural variations in COMT leading to the formation of inactive COMT that correlates with CPSP.

CONCLUSION

The results of the present study showed that both novel and previously reported mutations in COMT gene has strong association with CPSP.

OPRM1 and COMT polymorphisms: implications on postoperative acute, chronic and experimental pain after cardiac surgery

Aim: Investigate the potential role of OPRM1 (mu-opioid receptor) and COMT (catechol-O-methyltransferase enzyme) polymorphisms in postoperative acute, chronic and experimental thermal pain. Methods: A secondary analysis of 125 adult cardiac surgery patients that were randomized between fentanyl and remifentanil during surgery and genotyped. Results: Patients in the fentanyl group with the COMT high-pain sensitivity haplotype required less postoperative morphine compared with the average-pain sensitivity haplotype (19.4 [16.5; 23.0] vs 34.6 [26.2; 41.4]; p = 0.00768), but not to the low-pain sensitivity group (30.1 [19.1; 37.7]; p = 0.13). No association was found between COMT haplotype and other pain outcomes or OPRM1 polymorphisms and the different pain modalities. Conclusion: COMT haplotype appears to explain part of the variability in acute postoperative pain in adult cardiac surgery patients.

Non-specific analgesia during a clinical trial in fibromyalgia

BACKGROUND

When patients suffering from fibromyalgia undergo a therapeutic trial, a non-negligible part of analgesia is not explained by the drug itself. The mechanisms of this non-specific effect need to be understood.

MATERIALS AND METHODS

We undertook secondary analyses of a double-blind randomized trial in fibromyalgia patients in which 100 mg/day milnacipran was not found superior to placebo. Data from 49 patients belonging to both groups were pooled. Both before treatment and one month after treatment, all patients underwent a CaNTAB^® neuropsychological test (related to spatial planning, reaction time, decision-making and risk-taking, and ability to name objects), and measurements of sensation and pain thresholds to heat and cold, supraliminal heat pain threshold, punctuate mechanical pain threshold and temporal summation, mechanical allodynia to skin brushing, and response to conditioned pain modulation. We studied the baseline predictors of analgesia and the indicators of change associated to analgesia separately. A stepwise approach was used to select the factors to enter into the final ANCOVAs, in which age, body mass index, treatment group and pain at baseline were covariates.

RESULTS

No baseline predictor of non-specific analgesia other than pain at baseline was found to be predictive. Conversely, several neuropsychological (higher performance) or psychophysical (lower sensitivity) changes correlated with analgesia in unadjusted analyses. Multivariable analyses identified increases in warm/heat thermal thresholds and an increased ability to name objects, as factors associated with analgesia.

CONCLUSIONS

The changes observed concomitantly to non-specific pain analgesia might be related to mild changes in brain functioning, based on convergent literature data.

Role of inflammatory and pain genes polymorphisms in temporomandibular disorder and pressure pain sensitivity

OBJECTIVE

The aim of this study was to assess the correlation of inflammatory and pain genes polymorphisms with the presence of temporomandibular disorder (TMD) patients and with pressure pain sensitivity.

DESIGN

Data was collected from 268 consecutive subjects at Bauru School of Dentistry. Subjects aged younger than 20 years, with dental and neuropathic pain, sinusitis, cognitive and neurologic disorder were excluded. Included subjects were evaluated using the Research Diagnostic Criteria for Temporomandibular disorders and divided into two groups: TMD cases and healthy controls. Groups were submitted to pressure pain threshold (PPT) test for the temporomandibular joint, anterior temporalis and masseter muscles and genotyped for Val158Met, IL6-174, IL-1β-3954 and TNFA-308. Student's t-test and Pearson chi-square test were used to comparisons between groups. A linear multiple regression was used to evaluate the influence of genetics variables on the PPT and a bivariate analysis was used to assesses the influence of genetics variables on pain sensitivity below the PPT cut off of the structures in TMD group.

RESULTS

TMD group showed significantly lower PPT values for all structures when compared with control group (p < 0.001). SNP IL6-174 predicted higher pain sensitivity in the temporomandibular joint (p < 0.005) and in anterior temporalis muscle (p < 0.044) and SNP Val158Met in the masseter muscle (p < 0.038); when TMD group was divided according to PPT cut-off values the SNP Val158Met influenced increase pain sensibility in the masseter muscle.

CONCLUSION

TNFA-308 was associated with TMD and SNP IL6-174 and SNP Val158Met influenced pain sensitivity of patients with TMD.

Plasma Concentrations of Select Inflammatory Cytokines Predicts Pain Intensity 48 Hours Post-Shoulder Muscle Injury

OBJECTIVES

The relationship between elevated inflammatory cytokine levels and peak pain intensity following acute musculoskeletal injury has not been fully elucidated in high risk subgroups. Identifying the role that these cytokines have on pain responses may help with developing tailored therapeutic approaches.

METHODS

Data were collected from 54 participants who were vulnerable to a robust pain response and delayed recovery following musculoskeletal injury. Participants completed baseline active and resting pain measurements and a blood draw before an exercised induced shoulder muscle injury. Participants returned at 24 and 48 hours postinjury for follow-up pain measurements and blood draws. Blood plasma was analyzed for interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor α. Pearson bivariate correlations were performed between cytokines and pain measurements to identify candidate variables for stepwise multiple linear regression predicting pain intensity reports.

RESULTS

Pearson bivariate correlation identified 13/45 correlations between inflammatory cytokines and resting pain intensity and 9/45 between inflammatory cytokines and active pain (P<0.05, r≥0.3 or r≤-0.3). This led to 5 stepwise multiple linear regression models, of which 4 met the statistical criterion (P<0.0167); including IL-10 baseline plasma concentrations predicting active pain (r=0.19) and resting pain (r=0.15) intensity 48 hours postinjury. IL-6 and IL-10 plasma concentrations at 48 hours were respectively associated with active and resting pain at 48 hours.

DISCUSSION

These findings suggest that elevated concentrations of inflammatory cytokines, specifically IL-10 (at baseline and 48 h) and IL-6 (at 48 h), may play a role in heightened pain responses following exercise-induced muscle injury.

Effect of catechol-O-methyltransferase (rs4680) single-nucleotide polymorphism on opioid-induced hyperalgesia in adults with chronic pain

The catechol-O-methyltransferase Val158Met polymorphism has been associated with alterations in pain perception, but the influence of the polymorphism on pain perception in patients with chronic pain receiving daily opioid therapy has not been previously reported. The primary aim of this study was to investigate the effects of the catechol-O-methyltransferase Val158Met polymorphism on heat pain perception in a cohort of adults receiving daily opioid therapy for chronic pain. Adults with chronic pain consecutively admitted to an outpatient pain rehabilitation program who met inclusion criteria and were receiving daily opioid therapy were recruited for study participation (N = 142). Individuals were genotyped for catechol-O-methyltransferase Val158Met (rs4680), and the polymorphism was analyzed using an additive and codominant genotype models. The distribution of the Val158Met genotypes was 25% for Val/Val, 41% for Val/Met and 34% for Met/Met (Hardy-Weinberg, P > 0.05). A main effect of genotype was observed for heat pain perception ( P = 0.028). Under the codominant model of allele effects, exploratory post hoc pairwise comparisons adjusted for morphine equivalent dose and pain catastrophizing demonstrated that individuals with the Val/Met genotype were hyperalgesic compared to individuals with the Val/Val ( P = 0.039) and Met/Met ( P = 0.023) genotypes. No significant association was observed between heat pain perception and genotype under the additive model of allele effects. Among patients with chronic pain who were receiving daily opioids, the Val/Met genotype was associated with hyperalgesia using a measure of heat pain perception that has been previously indicative of opioid-induced hyperalgesia in other heterogeneous samples of adults with chronic pain. This study contributes to the emerging understanding of how catechol-O-methyltransferase activity affects pain perception in the context of daily opioid use, and these findings may be useful in the design of future trials aimed at investigating the potential efficacy of ß-2 adrenergic receptor antagonism for opioid-induced hyperalgesia.

Individual differences of maladaptive brain changes in migraine and their relationship with differential effectiveness of treatments

Migraine is a difficult disorder to identify with regard to its pathophysiological mechanisms, and its treatment has been primarily difficult owing to interindividual differences. Substantial rates of nonresponsiveness to medications are common, making migraine treatment complicated. In this review, we systematically analyzed recent studies concerning neuroimaging findings regarding the neurophysiology of migraine. We linked the current imaging research with anecdotal evidence from interindividual factors such as duration and pain intensity of migraine, age, gender, hormonal interplay, and genetics. These factors suggested the use of nonpharmacological therapies such as transcranial magnetic stimulation, transcranial direct current stimulation, and placebo therapy for the treatment of migraine. Finally, we discussed how interindividual differences are related to such nondrug treatments.

From transformation to chronification of migraine: pathophysiological and clinical aspects

Chronic migraine is a neurological disorder characterized by 15 or more headache days per month of which at least 8 days show typical migraine features. The process that describes the development from episodic migraine into chronic migraine is commonly referred to as migraine transformation or chronification. Ample studies have attempted to identify factors associated with migraine transformation from different perspectives. Understanding CM as a pathological brain state with trigeminovascular participation where biological changes occur, we have completed a comprehensive review on the clinical, epidemiological, genetic, molecular, structural, functional, physiological and preclinical evidence available.

Influences of COMT rs4680 and OPRM1 rs1799971 Polymorphisms on Chronic Postsurgical Pain, Acute Pain, and Analgesic Consumption After Elective Cesarean Delivery

OBJECTIVES

The main objectives of this study were to assess the effects of cathechol-O-methyl-transferase (COMT) rs4680 and μ-opioid receptor rs1799971 polymorphisms alone or genotype combinations on chronic postsurgical pain (CPSP), acute pain, and analgesic consumption after elective cesarean delivery in a Chinese cohort.

MATERIALS AND METHODS

Two hundred sixty-six patients undergoing elective cesarean delivery with a Pfannenstiel incision under spinal anesthesia were enrolled in this prospective, observational study. All patients were screened for rs4680 and rs1799971 using a peripheral venous blood sample of DNA. Postoperative pain relief was provided by IV patient-controlled analgesia with sufentanyl and tramadol for 48 hours postoperatively. Postoperative pain scores and analgesic consumption were assessed, and CPSP was evaluated 3 months after surgery in all patients.

RESULTS

Twenty-nine patients (29/266; 10.9%) developed CPSP at 3 months after surgery. The risk factors for CPSP included previous cesarean delivery and higher analgesic consumptions at 24 hours and 48 hours postoperatively (P=0.032, 0.015, and 0.008, reapectively). No associations were found between CPSP and a single rs4680 and rs1799971 polymorphism, or their combinations (P>0.05). In contrast, patients with rs1799971 GG required higher patient-controlled analgesics at 24 hours and 48 hours postoperatively compared with those with other genotypes (GG>AG>AA). However, no significant effects of interactions between the 2 single nucleotide polymorphisms on analgesic consumption were observed.

DISCUSSION

Our results indicate that cathechol-O-methyl-transferase rs4860 and μ-opioid receptor rs1799971 may not contribute to CPSP development after cesarean delivery. The genotype of rs1799971 affects postcesarean analgesic requirement, while the rs4680 do not. Additional larger studies are needed to confirm these findings.

Genetic variants in migraine: a field synopsis and systematic re-analysis of meta-analyses

OBJECTIVE

Numerous genetic variants from meta-analyses of observational studies and GWAS were reported to be associated with migraine susceptibility. However, due to the random errors in meta-analyses, the noteworthiness of the results showing statistically significant remains doubtful. Thus, we performed this field synopsis and re-analysis study to evaluate the noteworthiness using a Bayesian approach in hope of finding true associations.

METHODS

Relevant meta-analyses from observational studies and GWAS examining correlation between all genetic variants and migraine risk were included in our study by a PubMed search. Identification of noteworthy associations were analyzed by false-positive rate probability (FPRP) and Bayesian false discovery probability (BFDP). Using noteworthy variants, GO enrichment analysis were conducted through DAVID online tool. Then, the PPI network and hub genes were performed using STRING database and CytoHubba software.

RESULTS

As for 8 significant genetic variants from observational studies, none of which showed noteworthy at prior probability of 0.001. Out of 47 significant genetic variants in GWAS, 36 were noteworthy at prior probability of 0.000001 via FPRP or BFDP. We further found the pathways "positive regulation of cytosolic calcium ion concentration" and "inositol phosphate-mediated signaling" and hub genes including MEF2D, TSPAN2, PHACTR1, TRPM8 and PRDM16 related to migraine susceptibility.

CONCLUSION

Herein, we have identified several noteworthy variants for migraine susceptibility in this field synopsis. We hope these data would help identify novel genetic biomarkers and potential therapeutic target for migraine.

Placebo effects and the molecular biological components involved

Pharmacologically inactive substances have been used in medicine for more than 700 years and can trigger beneficial responses in the human body, which is referred to as the placebo effects or placebo responses. This effect is robust enough to influence psychosocial and physiological responses to the placebo and to active treatments in many settings, which has led to increased interest from researchers. In this article, we summarise the history of placebo, the characteristics of placebo effects and recent advancements reported from the studies on placebo effects and highlight placebome studies to identify various molecular biological components associated with placebo effects. Although placebos have a long history, the placebome concept is still in its infancy. Although behavioural, neurobiological and genetic studies have identified that molecules in the dopamine, opioid, serotonin and endocannabinoid systems might be targets of the placebo effect, placebome studies with a no-treatment control (NTC) are necessary to identify whole-genome genetic targets. Although bioinformatics analysis has identified the molecular placebome module, placebome studies with NTCs are also required to validate the related findings.