COMT val158met genotype affects mu-opioid neurotransmitter responses to a pain stressor

Neural indices of heritable impulsivity: Impact of the COMT Val158Met polymorphism on frontal beta power during early motor preparation

Studies of COMT Val158Met suggest that the neural circuitry subserving inhibitory control may be modulated by this functional polymorphism altering cortical dopamine availability, thus giving rise to heritable differences in behaviors. Using an anatomically-constrained magnetoencephalography method and stratifying the sample by COMT genotype, from a larger sample of 153 subjects, we examined the spatial and temporal dynamics of beta oscillations during motor execution and inhibition in 21 healthy Met158/Met158 (high dopamine) or 21 Val158/Val158 (low dopamine) genotype individuals during a Go/NoGo paradigm. While task performance was unaffected, Met158 homozygotes demonstrated an overall increase in beta power across regions essential for inhibitory control during early motor preparation (~100ms latency), suggestive of a global motor "pause" on behavior. This increase was especially evident on Go trials with slow response speed and was absent during inhibition failures. Such a pause could underlie the tendency of Met158 allele carriers to be more cautious and inhibited. In contrast, Val158 homozygotes exhibited a beta drop during early motor preparation, indicative of high response readiness. This decrease was associated with measures of behavioral disinhibition and consistent with greater extraversion and impulsivity observed in Val homozygotes. These results provide mechanistic insight into genetically-determined interindividual differences of inhibitory control with higher cortical dopamine associated with momentary response hesitation, and lower dopamine leading to motor impulsivity.

Effects of functional polymorphisms of opioid receptor mu 1 and catechol-O-methyltransferase on the neural processing of pain

AIM

Pain is reconstructed by brain activities and its subjectivity comes from an interplay of multiple factors. The current study aims to understand the contribution of genetic factors to the neural processing of pain. Focusing on the single-nucleotide polymorphism (SNP) of opioid receptor mu 1 (OPRM1) A118G (rs1799971) and catechol-O-methyltransferase (COMT) val158met (rs4680), we investigated how the two pain genes affect pain processing.

METHOD

We integrated a genetic approach with functional neuroimaging. We extracted genomic DNA information from saliva samples to genotype the SNP of OPRM1 and COMT. We used a percept-related model, in which two different levels of perceived pain intensities ("low pain: mildly painful" vs "high pain: severely painful") were employed as experimental stimuli.

RESULTS

Low pain involves a broader network relative to high pain. The distinct effects of pain genes were observed depending on the perceived pain intensity. The effects of low pain were found in supramarginal gyrus, angular gyrus, and anterior cingulate cortex (ACC) for OPRM1 and in middle temporal gyrus for COMT. For high pain, OPRM1 affected the insula and cerebellum, while COMT affected the middle occipital gyrus and ACC.

CONCLUSION

OPRM1 primarily affects sensory and cognitive components of pain processing, while COMT mainly influences emotional aspects of pain processing. The interaction of the two pain genes was associated with neural patterns coding for high pain and neural activation in the ACC in response to pain. The proteins encoded by the OPRM1 and COMT may contribute to the firing of pain-related neurons in the human ACC, a critical center for subjective pain experience.

The influence of COMT and ABCB1 gene polymorphisms on sufentanil analgesic effect for postoperative pain in children with fracture

The aim of this observational study was to investigate the effects of catechol-O-methyltransferase (COMT) and ATP-binding cassette transporter B1 (ABCB1) gene polymorphisms on the postoperative analgesic effect of sufentanil in Chinese Han pediatric patients with fractures. A total of 185 pediatric patients who underwent fracture surgery were included. Polymerase chain reaction-restriction fragment length polymorphism was used to detect the polymorphisms of COMT and ABCB1 genes. Sufentanil was used for postoperative analgesia. The pain level of the patients was evaluated using the face, legs, activity, cry, and consolability scale before surgery, during awakening, at 2, 6, 12, and 24 hours after surgery. The postoperative Ramsay sedation score, sufentanil consumption, and incidence of adverse reactions were also recorded. Pediatric patients with different genotypes of ABCB1 and COMT showed no statistically significant differences in general data such as age, gender, weight, height, surgical duration, and American Society of Anesthesiologists classification (P > .05). There were no statistically significant differences in sedation scores after surgery between different genotypes of ABCB1 and COMT (P > .05). Among patients with CC genotype in ABCB1, the pain scores and total consumption of sufentanil at awakening, 2 and 6 hours after surgery were higher compared to TT and CT genotypes (P < .05), while there were no statistically significant differences between TT and CT genotypes (P > .05). Among patients with AA genotype in COMT, the pain scores and total consumption of sufentanil at awakening, 2, 6, 12, and 24 hours after surgery were higher compared to AG and GG genotypes (P < .05), while there were no statistically significant differences between AG and GG genotypes (P > .05). There were no statistically significant differences in adverse reactions between different genotypes of ABCB1 and COMT (P > .05). The polymorphisms of COMT gene rs4680 and ABCB1 gene rs1045642 are associated with the analgesic effect and consumption of sufentanil in pediatric patients after fracture surgery.

A mouse model of chronic primary pain that integrates clinically relevant genetic vulnerability, stress, and minor injury

Chronic primary pain conditions (CPPCs) affect over 100 million Americans, predominantly women. They remain ineffectively treated, in large part because of a lack of valid animal models with translational relevance. Here, we characterized a CPPC mouse model that integrated clinically relevant genetic (catechol-O-methyltransferase; COMT knockdown) and environmental (stress and injury) factors. Compared with wild-type mice, Comt+/- mice undergoing repeated swim stress and molar extraction surgery intervention exhibited pronounced multisite body pain and depressive-like behavior lasting >3 months. Comt+/- mice undergoing the intervention also exhibited enhanced activity of primary afferent nociceptors innervating hindpaw and low back sites and increased plasma concentrations of norepinephrine and pro-inflammatory cytokines interleukin-6 (IL-6) and IL-17A. The pain and depressive-like behavior were of greater magnitude and longer duration (≥12 months) in females versus males. Furthermore, increases in anxiety-like behavior and IL-6 were female-specific. The effect of COMT genotype × stress interactions on pain, IL-6, and IL-17A was validated in a cohort of 549 patients with CPPCs, demonstrating clinical relevance. Last, we assessed the predictive validity of the model for analgesic screening and found that it successfully predicted the lack of efficacy of minocycline and the CB2 agonist GW842166X, which were effective in spared nerve injury and complete Freund's adjuvant models, respectively, but failed in clinical trials. Yet, pain in the CPPC model was alleviated by the beta-3 adrenergic antagonist SR59230A. Thus, the CPPC mouse model reliably recapitulates clinically and biologically relevant features of CPPCs and may be implemented to test underlying mechanisms and find new therapeutics.

Pain-related single nucleotide polymorphisms: association with lumbar spinal stenosis patient experience and non-surgical treatment outcomes

PURPOSE

Lumbar spinal stenosis (LSS) is common in our aging population resulting in pain and functional impairment. Recent advances in pain research have identified several single nucleotide polymorphisms (SNP) associated with inter-individual symptom and treatment response. The goal of the current study was to investigate the association of SNPs in Neuropeptide Y (NPY) and Catechol-O-methyltransferase (COMT) with pain, function, and treatment outcomes in Lumbar spinal stenosis (LSS) patients receiving non-surgical treatments.

METHODS

An exploratory observational biomarker study was performed ancillary to a previously published clinical trial evaluating three different non-surgical treatments for LSS. Saliva samples were obtained for single nucleotide polymorphism genotyping and blood samples were collected for NPY protein. Data on pain and function collected as part of the clinical trial at baseline, 2 and 6 months were examined for association with known polymorphisms in NPY and COMT.

RESULTS

Subjects with the NPY rs16147 TT genotype exhibited higher baseline symptom severity but also a higher likelihood of responding to non-surgical treatments. Subjects with the COMT rs4680 GG genotype also exhibited higher baseline symptom severity but did not demonstrate greater response to treatment.

CONCLUSIONS

NPY rs16147 and COMT rs4680 are important potential biomarkers associated with pain and function. NPY genotype may be useful in predicting response to non-surgical treatments in older adults with LSS.

Association of oral behaviours and psychological factors with selected genotypes in pain-related TMD

OBJECTIVES

To investigate frequency of single nucleotide polymorphisms (SNPs) in pain-related temporomandibular disorders (TMDp) and to determine whether specific SNPs, psychological, psychosomatic and behavioural characteristics are predictive for pain existence and intensity (low pain intensity (LPI)/high pain intensity (HPI)).

METHODS

Genomic DNA was extracted from buccal mucosa swabs (85 TMDp;85 controls) for evaluating frequency of selected SNPs: catechol-O-methyltransferase (rs4680, rs4818), opiorphin (rs1387964), alpha subunit of voltage-gated sodium channel Nav1.1 (rs6432860) and voltage-gated sodium channel Nav1.9 (rs33985936). Participants completed questionnaires on somatosensory amplification, anxiety and depression symptoms and oral behaviours (OB).

RESULTS

Sleep-related OB frequency was higher in TMDp patients compared to controls (p = 0.008). Compared to LPI, HPI patients had higher depression (p = 0.020) and anxiety scores (p = 0.017). TMDp group showed higher frequency of CC genotype (rs1387964) than controls (12.9% vs. 3.5%, p = 0.025). Following adjustments for age, sex and sleep-related OB, the significance of the recessive model (CC vs. TC + TT) between TMDp patients and controls was retained (OR = 5.783; 95%CI: 1.454-23.004). Frequency of GG genotype (rs4680 and rs4818) was higher in HPI compared to LPI patients (40% vs. 11.4%, p = 0.006; 24% vs. 3%; p = 0.012, respectively). The difference remained significant after adjusting for age, sex, depression, anxiety and sleep-related OB (rs4680: OR = 3.621; 95%CI: 1.580-8.297; rs4818: OR = 4.919, 95%CI: 1.641-14.746).

CONCLUSION

This study has demonstrated that rs1387964 CC genotype was associated with TMDp while rs4680 GG and rs4818 GG genotypes contributed to HPI.

Moderating effects of preoperative knee pain and pain catastrophizing on the relation between COMT rs4680 genotypes and chronic postsurgical pain in total knee arthroplasty patients

BACKGROUND

The Catechol-O-methyltransferase (COMT) gene, responsible for encoding an enzyme crucial in the metabolism of catecholamines, is known to play a significant role in pain perception. Polymorphisms within this gene, particularly the COMT rs4680 genotypes, have been linked to various acute pain phenotypes. This prospective cohort study examines interactions among the genetic polymorphism COMT rs4680 genotypes, preoperative knee pain, and pain catastrophizing in chronic postsurgical pain (CPSP) at 3, 6, and 12 months post-total knee arthroplasty (TKA).

STUDY DESIGN

A total of 280 patients undergoing primary unilateral TKA participated, sharing demographic details, preoperative knee pain levels, psychological variables (pain catastrophizing), and COMT rs4680 genotyping via venous blood samples. Telephone interviews at specified intervals enabled the application of binary logistic regressions and interaction models.

RESULTS

Significant influences of preoperative knee pain and pain catastrophizing on postsurgical outcomes were observed. Specifically, at the first time point (T1, 3 months post-TKA), a notable moderation effect was identified in preoperative knee pain (R2 change = 0.026, p = 0.026). The Johnson-Neyman regions of significance (RoS) indicated these moderation effects were significant above a threshold of 17.18 (p = 0.05), accounting for 26.4%. At the third time point (T3, 12 months post-TKA), a complex three-way interaction among genotypes (GG, GA, and AA carriers) was evident, resulting in an R2 change of 0.051 (p = 0.009). Here, the RoS for pain catastrophizing was above 32.74 for 30.5% of GG genotype carriers, above 22.38 for 50.8% of GA carriers, and below 11.94 for 63.2% of AA carriers.

CONCLUSION

This study illuminates the significant role of the COMT Val158Met rs4680 polymorphism in susceptibility to prolonged pain following TKA. It also elucidates how these genetic genotypes interplay with preoperative knee pain and pain catastrophizing. Such intricate genetic-psychological-pain relationships necessitate additional investigation to confirm these findings and potentially guide post-TKA pain management strategies.

IUPHAR review: Navigating the role of preclinical models in pain research

Chronic pain is a complex and challenging medical condition that affects millions of people worldwide. Understanding the underlying mechanisms of chronic pain is a key goal of preclinical pain research so that more effective treatment strategies can be developed. In this review, we explore nociception, pain, and the multifaceted factors that lead to chronic pain by focusing on preclinical models. We provide a detailed look into inflammatory and neuropathic pain models and discuss the most used animal models for studying the mechanisms behind these conditions. Additionally, we emphasize the vital role of these preclinical models in developing new pain-relief drugs, focusing on biologics and the therapeutic potential of NMDA and cannabinoid receptor antagonists. We also discuss the challenges of TRPV1 modulation for pain treatment, the clinical failures of neurokinin (NK)- 1 receptor antagonists, and the partial success story of Ziconotide to provide valuable lessons for preclinical pain models. Finally, we highlight the overall success and limitations of current treatments for chronic pain while providing critical insights into the development of more effective therapies to alleviate the burden of chronic pain.

Epigenetic Connections of the TRPA1 Ion Channel in Pain Transmission and Neurogenic Inflammation - a Therapeutic Perspective in Migraine?

Persistent reprogramming of epigenetic pattern leads to changes in gene expression observed in many neurological disorders. Transient receptor potential cation channel subfamily A member 1 (TRPA1), a member of the TRP channels superfamily, is activated by many migraine triggers and expressed in trigeminal neurons and brain regions that are important in migraine pathogenesis. TRP channels change noxious stimuli into pain signals with the involvement of epigenetic regulation. The expression of the TRPA1 encoding gene, TRPA1, is modulated in pain-related syndromes by epigenetic alterations, including DNA methylation, histone modifications, and effects of non-coding RNAs: micro RNAs (miRNAs), long non-coding RNAs, and circular RNAs. TRPA1 may change epigenetic profile of many pain-related genes as it may modify enzymes responsible for epigenetic modifications and expression of non-coding RNAs. TRPA1 may induce the release of calcitonin gene related peptide (CGRP), from trigeminal neurons and dural tissue. Therefore, epigenetic regulation of TRPA1 may play a role in efficacy and safety of anti-migraine therapies targeting TRP channels and CGRP. TRPA1 is also involved in neurogenic inflammation, important in migraine pathogenesis. The fundamental role of TRPA1 in inflammatory pain transmission may be epigenetically regulated. In conclusion, epigenetic connections of TRPA1 may play a role in efficacy and safety of anti-migraine therapy targeting TRP channels or CGRP and they should be further explored for efficient and safe antimigraine treatment. This narrative/perspective review presents information on the structure and functions of TRPA1 as well as role of its epigenetic connections in pain transmission and potential in migraine therapy.

Relationship between COMT Gene Polymorphism, Anxiety, and Pain Perception during Labour

BACKGROUND

The COMT gene polymorphism is associated with neurological and psychiatric disorders and pain perception. The present study investigates the existence of anxiety and pain perception in relation to the COMT (catechol-O-methyltransferase) gene polymorphism in labouring women (during "natural" childbirth) with or without inhaled analgesia.

METHODS

A total of 181 women who chose vaginal birth were enrolled in this study. To present the difference in pain perception, the parturients were divided into one group (n = 90) that chose labour analgesia with inhaled nitrous oxide (50% nitrous oxide and 50% oxygen) and one group (n = 91) without analgesia. The blood samples were taken during the pregnancy as a part of routine pregnancy controls in the hospital. The COMT gene polymorphism was detected with the PCR technique. The pain perception of parturients was self-evaluated two times according to the VAS (Visual Analogue Scale), and anxiety as a personality trait was determined with the STAI-T (State Trait Anxiety Inventory). Pain perception as well as anxiety were compared according to COMT genotypes.

RESULTS

In the 181 pregnant women, there were 40 women (22%) of wild homozygotes (GG) of COMT, 95 women (53%) of mutant heterozygotes (GA), and 46 women (25%) of mutant homozygotes (AA). A negative association of pain perception with the GA (mutant heterozygote) polymorphism of the COMT gene versus the wild-type (GG polymorphism) was observed. The GA polymorphism of the COMT gene was associated with 0.46 units lower pain perception compared to the wild type (GG). The anxiety trait score in group AA was lower than in groups GA and GG. The difference reached statistical significance only when comparing AA versus GA (p > 0.042). Analgesic efficacy of nitrous oxide was noticed in 22% of labouring women who reported moderate pain (VAS score 4-7).

CONCLUSIONS

The COMT gene polymorphism was associated with pain perception and anxiety among parturients. The COMT gene polymorphism GA was associated with negative pain perception among labouring women. Nitrous oxide showed statistical significance in anxiolytic efficacy during labour in women with mild anxiety as a personality trait. Anxiolytic efficacy of nitrous oxide has shown better efficacy in parturients with the COMT gene polymorphism AA.

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.

Impact of Genetic Variants on Postoperative Pain and Fentanyl Dose Requirement in Patients Undergoing Major Breast Surgery: A Candidate Gene Association Study

BACKGROUND

Postoperative analgesia is crucial for the early and effective recovery of patients undergoing surgery. Although postoperative multimodal analgesia is widely practiced, opioids such as fentanyl are still one of the best analgesics. The analgesic response of fentanyl varies widely among individuals, probably due to genetic and nongenetic factors. Among genetic factors, single nucleotide polymorphisms (SNPs) may influence its analgesic response by altering the structure or function of genes involved in nociceptive, fentanyl pharmacodynamic, and pharmacokinetic pathways. Thus, it is necessary to comprehensively ascertain if the SNPs present in the aforementioned pathways are associated with interindividual differences in fentanyl requirement. In this study, we evaluated the association between 10 candidate SNPs in 9 genes and 24-hour postoperative fentanyl dose (primary outcome) and also with postoperative pain scores and time for first analgesia (secondary outcomes).

METHODS

A total of 257 South Indian women, aged 18-70 years, with American Society of Anesthesiologists (ASA) physical status I-III, undergoing major breast surgery under general anesthesia, were included in the study. Patients were genotyped for candidate SNPs using real-time polymerase chain reaction. All patients received a standardized intravenous fentanyl infusion through a patient-controlled analgesic (PCA) pump, and the 24-hour postoperative fentanyl dose requirement was measured using PCA.

RESULTS

The median 24-hour postoperative fentanyl requirement was higher in rs1799971 carriers (G/G versus A/A + A/G-620 μg [500-700] vs 460 μg [400-580]) with a geometric mean (GM) ratio of 1.91 (95% confidence interval [CI], 1.071-1.327). The median 24-hour pain scores were higher in rs4680 carriers (A/G + A/A versus G/G-34 [30-38] vs 31 [30-38]) with a GM ratio of 1.059 (95% CI, 1.018-1.101) and were lower in rs1045642 carriers (A/A + A/G versus G/G-34 [30-38] vs 30 [30-34]) with a GM ratio of 0.936 (95% CI, 0.889-0.987). The median time for first analgesic was lower in rs734784 carriers [C/C versus T/T + C/T-240 minutes (180-270) vs 240 minutes (210-270)] with a GM ratio of 0.902 (95% CI, 0.837-0.972). Five of 9 clinical factors, namely, history of diabetes, hypertension, hypothyroidism, anesthesia duration, and intraoperative fentanyl requirement were associated with different outcomes individually ( P < .05) and were used to adjust the respective associations.

CONCLUSIONS

The SNP opioid receptor mu-1 ( OPRM1 ) (rs1799971) was associated with higher postoperative fentanyl requirement in South Indian patients undergoing major breast surgery. Twenty-four hour postoperative pain scores were higher in catechol-O-methyl transferase ( COMT ) (rs4680) carriers and lower in ATP binding cassette subfamily B member 1 ( ABCB1 ) (rs1045642) carriers, whereas time for first analgesic was lower in potassium channel subunit 1 ( KCNS1 ) (rs734784) carriers. However, these exploratory findings must be confirmed in a larger study.

Pharmacogenetic Guided Opioid Therapy Improves Chronic Pain Outcomes and Comorbid Mental Health: A Randomized, Double-Blind, Controlled Study

Interindividual variability in analgesic response is at least partly due to well-characterized polymorphisms that are associated with opioid dosing and adverse outcomes. The Clinical Pharmacogenetics Implementation Consortium (CPIC) has put forward recommendations for the CYP2D6 phenotype, but the list of studied drug-gene pairs continues to grow. This clinical trial randomized chronic pain patients (n = 60), referred from primary care to pain unit care into two opioid prescribing arms, one guided by CYP2D6, μ-opioid receptor (OPRM1), and catechol-O-methyl transferase (COMT) genotypes vs. one with clinical routine. The genotype-guided treatment reduced pain intensity (76 vs. 59 mm, p < 0.01) by improving pain relief (28 vs. 48 mm, p < 0.05), increased quality of life (43 vs. 56 mm p < 0.001), and lowered the incidence of clinically relevant adverse events (3 [1-5] vs. 1 [0-2], p < 0.01) and 42% opioid dose (35 [22-61] vs. 60 [40-80] mg/day, p < 0.05) as opposed to usual prescribing arm. The final health utility score was significantly higher (0.71 [0.58-0.82] vs. 0.51 [0.13-0.67] controls, p < 0.05) by improving sleepiness and depression comorbidity, with a significant reduction of 30-34% for headache, dry mouth, nervousness, and constipation. A large-scale implementation analysis could help clinical translation, together with a pharmaco-economic evaluation.

Role of GABAergic system in the comorbidity of pain and depression

Patients with chronic pain often suffer with depressive symptoms, and these two conditions can be aggravated by each other over time, leading to an increase in symptom intensity and duration. The comorbidity of pain and depression poses a significant challenge to human health and quality of life, as it is often difficult to diagnose early and treat effectively. Therefore, exploring the molecular mechanisms underlying the comorbidity of chronic pain and depression is crucial to identifying new therapeutic targets for treatment. However, understanding the pathogenesis of comorbidity requires examining interactions among multiple factors, which calls for an integrative perspective. While several studies have explored the role of the GABAergic system in pain and depression, fewer have examined its interactions with other systems involved in their comorbidity. Here, we review the evidence that the role of GABAergic system in the comorbidity of chronic pain and depression, as well as the interactions between the GABAergic system and other secondary systems involved in pain and depression comorbidity, providing a comprehensive understanding of their intricate interplay.

Pharmacogenetic Analysis Enables Optimization of Pain Therapy: A Case Report of Ineffective Oxycodone Therapy

Patients suffering from chronic pain may respond differently to analgesic medications. For some, pain relief is insufficient, while others experience side effects. Although pharmacogenetic testing is rarely performed in the context of analgesics, response to opiates, non-opioid analgesics, and antidepressants for the treatment of neuropathic pain can be affected by genetic variants. We describe a female patient who suffered from a complex chronic pain syndrome due to a disc hernia. Due to insufficient response to oxycodone, fentanyl, and morphine in addition to non-steroidal anti-inflammatory drug (NSAID)-induced side effects reported in the past, we performed panel-based pharmacogenotyping and compiled a medication recommendation. The ineffectiveness of opiates could be explained by a combined effect of the decreased activity in cytochrome P450 2D6 (CYP2D6), an increased activity in CYP3A, and an impaired drug response at the µ-opioid receptor. Decreased activity for CYP2C9 led to a slowed metabolism of ibuprofen and thus increased the risk for gastrointestinal side effects. Based on these findings we recommended hydromorphone and paracetamol, of which the metabolism was not affected by genetic variants. Our case report illustrates that an in-depth medication review including pharmacogenetic analysis can be helpful for patients with complex pain syndrome. Our approach highlights how genetic information could be applied to analyze a patient's history of medication ineffectiveness or poor tolerability and help to find better treatment options.

A Comprehensive Review of the Genetic and Epigenetic Contributions to the Development of Fibromyalgia

This narrative review summarizes the current knowledge of the genetic and epigenetic contributions to the development of fibromyalgia (FM). Although there is no single gene that results in the development of FM, this study reveals that certain polymorphisms in genes involved in the catecholaminergic pathway, the serotonergic pathway, pain processing, oxidative stress, and inflammation may influence susceptibility to FM and the severity of its symptoms. Furthermore, epigenetic changes at the DNA level may lead to the development of FM. Likewise, microRNAs may impact the expression of certain proteins that lead to the worsening of FM-associated symptoms.

Point-of-Care Testing of Enzyme Polymorphisms for Predicting Hypnotizability and Postoperative Pain

Hypnotizability is a stable trait that moderates the benefit of hypnosis for treating pain, but limited availability of hypnotizability testing deters widespread use of hypnosis. Inexpensive genotyping of four single-nucleotide polymorphisms in the catechol-o-methyltransferase (COMT) gene was performed using giant magnetoresistive biosensors to determine if hypnotizable individuals can be identified for targeted hypnosis referrals. For individuals with the proposed optimal COMT diplotypes, 89.5% score highly on the Hypnotic Induction Profile (odds ratio, 6.12; 95% CI, 1.26-28.75), which identified 40.5% of the treatable population. Mean hypnotizability scores of the optimal group were significantly higher than the total population (P = 0.015; effect size = 0.60), an effect that was present in women (P = 0.0015; effect size = 0.83), but not in men (P = 0.28). In an exploratory cohort, optimal individuals also reported significantly higher postoperative pain scores (P = 0.00030; effect size = 1.93), indicating a greater need for treatment.

Catechol-O-Methyltransferase Loss Drives Cell-Specific Nociceptive Signaling via the Enteric Catechol-O-Methyltransferase/microRNA-155/Tumor Necrosis Factor α Axis

BACKGROUND & AIMS

The etiology of abdominal pain in postinfectious, diarrhea-predominant irritable bowel syndrome (PI-IBS-D) is unknown, and few treatment options exist. Catechol-O-methyltransferase (COMT), an enzyme that inactivates and degrades biologically active catecholamines, plays an important role in numerous physiologic processes, including modulation of pain perception. Our objective was to determine the mechanism(s) of how decreased colonic COMT in PI-IBS-D patients contributes to the chronic abdominal pain phenotype after enteric infections.

METHODS

Colon neurons, epithelial cells, and macrophages were procured with laser capture microdissection from PI-IBS-D patients to evaluate cell-specific colonic COMT, microRNA-155 (miR-155), and tumor necrosis factor (TNF) α expression levels compared to recovered patients (infection cleared: did not develop PI-IBS-D) and control individuals. COMT-/-, colon-specific COMT-/-, and miR-155-/- mice and human colonoids were used to model phenotypic expression of COMT in PI-IBS-D patients and to investigate signaling pathways linking abdominal pain. Citrobacter rodentium and trinitrobenzene sulfonic acid animal models were used to model postinflammatory changes seen in PI-IBS-D patients.

RESULTS

Colonic COMT levels were significantly decreased and correlated with increased visual analog scale abdominal pain ratings in PI-IBS-D patients compared to recovered patients and control individuals. Colonic miR-155 and TNF-α were increased in PI-IBS-D patients with diminished colonic COMT. COMT-/- mice had significantly increased expression of miR-155 and TNF-α in both colon tissues and dorsal root ganglia. Introduction of cV1q antibody (anti-TNF-α) into mice reversed visceral hypersensitivity after C rodentium and trinitrobenzene sulfonic acid.

CONCLUSIONS

Decreased colonic COMT in PI-IBS-D patients drives abdominal pain phenotypes via the COMT/miR-155/TNF-α axis. These important findings will allow new treatment paradigms and more targeted and personalized medicine approaches for gastrointestinal disorders after enteric infections.

Classification and Diagnosis of Temporomandibular Disorders and Temporomandibular Disorder Pain

Designing classification systems and developing diagnostic criteria for temporomandibular disorders is difficult. An appreciation of the utility and applicability of these entities requires an understanding of the importance of each, the differences between the two, and how they may be optimally operationalized for both clinical and research activities in light of their inherent advantages and limitations. In addition, consideration for adopting newer approaches, such as following ontological and precision-based medicine principles, accounting for genetics/epigenetic and neurobiological factors, and the inclusion of biomarkers will potentially result in more thorough and comprehensive classification systems and diagnostic criteria.

Morphine Versus Oxycodone for Cancer Pain Using a Catechol-O-methyltransferase Genotype Biomarker: A Multicenter, Randomized, Open-Label, Phase III Clinical Trial (RELIEF Study)

BACKGROUND

We hypothesized that the high-dose opioid requirement in patients carrying the rs4680-GG variant in the COMT gene encoding catechol-O-methyltransferase would be greater for patients taking morphine than for those taking oxycodone, thus providing a much-needed biomarker to inform opioid selection for cancer pain.

METHODS

A randomized, multicenter, open-label trial was conducted at a Japanese hospital's palliative care service. Patients with cancer pain treated with regular doses of nonsteroidal anti-inflammatory drugs or acetaminophen were enrolled and randomized (1:1) into morphine (group M) and oxycodone (group O) groups. The minimum standard dose of immediate-release (IR) oral opioids was repeatedly administered by palliative care physicians to achieve pain-reduction goals (Pain reduction ≥ 33% from baseline and up to ≤ 3 on a numerical rating scale). The primary endpoint was the proportion of subjects requiring high-dose opioids on day 0 with the GG genotype.

RESULTS

Of 140 participants who developed cancer-related pain among 378 subjects registered and pre-screened for the genotype, 139 were evaluated in the current study. Among patients carrying a COMT rs4680-GG genotype, 48.3% required high-dose opioids in group M, compared with the 20.0% in group O (95% CI, 3.7%-50.8%; P = .029). Of those with the non-GG genotype, 41.5% treated with morphine and 23.1% with oxycodone required high-dose opioids (95% CI, 3.3%-38.3%; P = 0.098).

CONCLUSION

Using the COMT rs4680 genotype alone is not recommended for selecting between morphine and oxycodone for pain relief.

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.

Pharmacological data science perspective on fatal incidents of morphine treatment

Morphine prescribed for analgesia has caused drug-related deaths at an estimated incidence of 0.3% to 4%. Morphine has pharmacological properties that make it particularly difficult to assess the causality of morphine administration with a patient's death, such as its slow transfer between plasma and central nervous sites of action and the existence of the active metabolite morphine-6-glucuronide with opioid agonistic effects, Furthermore, there is no well-defined toxic dose or plasma/blood concentration for morphine. Dosing is often adjusted for adequate pain relief. Here, we summarize reported deaths associated with morphine therapy, including associated morphine exposure and modulating patient factors such as pharmacogenetics, concomitant medications, or comorbidities. In addition, we systematically analyzed published numerical information on the stability of concentrations of morphine and its relevant metabolites in biological samples collected postmortem. A medicolegal case is presented in which the causality of morphine administration with death was in dispute and pharmacokinetic modeling was applied to infer the administered dose. The results of this analytical review suggest that (i) inference from postmortem blood concentrations to the morphine dose administered has low validity and (ii) causality between a patient's death and the morphine dose administered remains a highly context-dependent and collaborative assessment among experts from different medical specialties.

Effects of DRD2/ANKK1 and COMT Val158Met polymorphisms on stabilization against and adaptation to unexpected events

Genetic variations affecting dopaminergic neuromodulation such as the DRD2/ANKK1 and the COMT Val158Met polymorphisms contribute to goal-directed behavior that requires a balance between stabilization and updating of current states and behaviors. Dopamine is also thought to be relevant for encoding of surprise signals to sensory input and adaptive learning. A link between goal-directed behavior and learning from surprise is therefore plausible. In the present fMRI study, we investigated whether DRD2 and COMT polymorphisms are related to behavioral responses and neural signals in the caudate nucleus and dlPFC during updating or stabilizing internal models of predictable digit sequences. To-be-detected switches between sequences and to-be-ignored digit omissions within a sequence varied by information-theoretic quantities of surprise and entropy. We found that A1 noncarriers and Val-carriers showed a lower response threshold along with increased caudate and dlPFC activation to surprising switches compared with A1-carriers and Met-homozygotes, whose dlPFC activity increased with decreasing switch surprise. In contrast, there were overall smaller differences in behavioral and neural modulation by drift surprise. Our results suggest that the impact of dopamine-relevant polymorphisms in the flexibility-stability trade-off may result in part from the role of dopamine in encoding the weight afforded to events requiring updating or stabilization.

Pain predict genetics: protocol for a prospective observational study of clinical and genetic factors to predict the development of postoperative pain

INTRODUCTION

Postoperative pain remains a challenging medical condition impacting the quality of life of every patient. Although several predictive factors for postoperative pain have been identified, an adequate prediction of postoperative pain in patients at risk has not been achieved yet.The primary objective of this study is to identify specific genetic risk factors for the development of acute and chronic postoperative pain to construct a prediction model facilitating a more personalised postoperative pain management for each individual. The secondary objectives are to build a databank enabling researchers to identify other risk factors for postoperative pain, for instance, demographic and clinical outcome indicators; provide insight into (genetic) factors that predict pharmacological pain relief; investigate the relationship between acute and chronic postoperative pain.

METHODS AND ANALYSIS

In this prospective, observational study, patients who undergo elective surgery will be recruited to a sample size of approximately 10 000 patients. Postoperative acute and chronic pain outcomes will be collected through questionnaires at different time points after surgery in the follow-up of 6 months. Potential genetic, demographic and clinical risk factors for prediction model construction will be collected through blood, questionnaires and electronic health records, respectively.Genetic factors associated with acute and/or chronic postoperative pain will be identified using a genome-wide association analysis. Clinical risk factors as stated in the secondary objectives will be assessed by multivariable regression. A clinical easy-to-use prediction model will be created for postoperative pain to allow clinical use for the stratification of patients.

ETHICS AND DISSEMINATION

The Institutional Review Board of the Radboud university medical centre approved the study (authorisation number: 2012/117). The results of this study will be made available through peer-reviewed scientific journals and presentations at relevant conferences, which will finally contribute to personalised postoperative pain management.

TRIAL REGISTRATION NUMBER

NCT02383342.

Genetic and epigenetic regulation of Catechol-O-methyltransferase in relation to inflammation in chronic fatigue syndrome and Fibromyalgia

BACKGROUND

Catechol-O-methyltransferase (COMT) has been shown to influence clinical pain, descending modulation, and exercise-induced symptom worsening. COMT regulates nociceptive processing and inflammation, key pathophysiological features of Chronic Fatigue Syndrome and Fibromyalgia (CFS/FM). We aimed to determine the interactions between genetic and epigenetic mechanisms regulating COMT and its influence on inflammatory markers and symptoms in patients with CFS/FM.

METHODS

A case-control study with repeated-measures design was used to reduce the chance of false positive and increase the power of our findings. Fifty-four participants (28 patients with CFS/FM and 26 controls) were assessed twice within 4 days. The assessment included clinical questionnaires, neurophysiological assessment (pain thresholds, temporal summation, and conditioned pain modulation), and blood withdrawal in order to assess rs4818, rs4633, and rs4680 COMT polymorphisms and perform haplotype estimation, DNA methylation in the COMT gene (both MB-COMT and S-COMT promoters), and cytokine expression (TNF-α, IFN-γ, IL-6, and TGF-β).

RESULTS

COMT haplotypes were associated with DNA methylation in the S-COMT promoter, TGF-β expression, and symptoms. However, this was not specific for one condition. Significant between-group differences were found for increased DNA methylation in the MB-COMT promoter and decreased IFN-γ expression in patients.

DISCUSSION

Our results are consistent with basic and clinical research, providing interesting insights into genetic-epigenetic regulatory mechanisms. MB-COMT DNA methylation might be an independent factor contributing to the pathophysiology of CFS/FM. Further research on DNA methylation in complex conditions such as CFS/FM is warranted. We recommend future research to employ a repeated-measure design to control for biomarkers variability and within-subject changes.

No Association between Genetic Variants of the COMT and OPRM1 Genes and Pain Perception among Patients Undergoing Total Hip or Knee Arthroplasty for Primary Osteoarthritis

Each year approximately 1 million total hip replacements are performed worldwide. The most common indications to choose this procedure are rest pain and pain after activity as well as functional limitations influencing daily activities. Experimental pain is highly variable by individuals, which is partly due to genetics. The aim of the study was to investigate a possible association of the catechol-O-methyltransferase (COMT) and μ-opioid receptor (OPRM1) genotypes with pain perception in patients undergoing total hip replacement and total knee replacement taking into account aspects such as age, sex and diabetes. The study included 207 patients (119 females, 88 males, median age 65 years, range 33−77) that qualified for surgical treatment (total hip replacement and knee arthroplasty) due to osteoarthritis. Pain sensitivity measurement was performed using a standard algometer. The genomic DNA was extracted from the buccal cells.. Single locus analysis was conducted using a general linear model. In the study group, we did not find statistically significant genetic associations between variants of COMT and OPRM1 and pain thresholds/pain tolerance. The analysis of subjective pain perception using the visual analog scale did not show any relationship between the OPRM1 rs1799971A>G variant and COMT rs4680, rs4633, rs4818 and rs6269.

Unique and joint associations of polygenic risk for major depression and opioid use disorder with endogenous opioid system function

Major depressive disorder (MDD) and opioid use disorder (OUD) are common, potentially fatal, polygenic disorders that are moderately heritable and often co-occur. We examined the unique and shared associations of polygenic risk scores (PRS) for these disorders with µ-opioid receptor (MOR) concentration and endogenous opioid response during a stressful stimulus. Participants were 144 healthy European-ancestry (EA) subjects (88 females) who underwent MOR quantification scans with [11C]carfentanil and PET and provided DNA for genotyping. MOR non-displaceable binding potential (BPND) was measured in 5 regions of interest (ROIs) related to mood and addiction. We examined associations of PRS both at baseline and following opioid release calculated as the ratio of baseline and stress-challenge scans, first in the entire sample and then separately by sex. MOR availability at baseline was positively associated with MDD PRS in the amygdala and ventral pallidum. MDD and OUD PRS were significantly associated with stress-induced opioid system activation in multiple ROIs, accounting for up to 14.5% and 5.4%, respectively, of the variance in regional activation. The associations were most robust among females, where combined they accounted for up to 25.0% of the variance among the ROIs. We conclude that there is a pathophysiologic link between polygenic risk for MDD and OUD and opioid system activity, as evidenced by PRS with unique and overlapping regional associations with this neurotransmitter system. This link could help to explain the high rate of comorbidity of MDD and OUD and suggests that opioid-modulating interventions could be useful in treating MDD and OUD, both individually and jointly.

Correlations between COMT polymorphism and brain structure and cognition in elderly subjects: An observational study

The catechol-O-methyltransferase (COMT) gene has been noted to play an important role in individual variations in the aging process. We investigated whether COMT polymorphism could influence cognition related to white matter networks. More specifically, we examined whether methionine (Met) allele loading is associated with better individual cognitive performance. Thirty-four healthy elderly participants were recruited; each participant's COMT genotype was determined, and Korean version of Montreal Cognitive Assessment scores and a diffusion tensor image were obtained for all participants. The Met carrier group showed significantly lower mean diffusivity, axial diffusivity, and radial diffusivity values for the right hippocampus, thalamus, uncinate fasciculus, and left caudate nucleus than the valine homozygote group. The Met carrier group also scored higher for executive function and attention on the Korean version of Montreal Cognitive Assessment. Based on these results, we can assume that the COMT Met allele has a protective effect on cognitive decline contributing to individual differences in cognitive function in late life period.

Reliability of conditioned pain modulation in healthy individuals and chronic pain patients: a systematic review and meta-analysis

OBJECTIVES

Conditioned pain modulation (CPM) is a psychophysical parameter that is used to reflect the efficacy of endogenous pain inhibition. CPM reliability is important for research and potential clinical applications. The aim of this systematic review and meta-analysis was to evaluate the reliability of CPM tests in healthy individuals and chronic pain patients.

METHODS

We searched three databases for peer-reviewed studies published from inception to October 2020: EMBASE, Web of Science and NCBI. Risk of bias and the quality of the included studies were assessed. A meta-analysis with a random effects model was conducted to estimate intraclass correlation coefficients (ICCs).

RESULTS

Meta-analysis was performed on 25 papers that examined healthy participants (k=21) or chronic pain patients (k=4). The highest CPM intra-session reliability was with pressure as test stimulus (TS) and ischemic pressure (IP) or cold pressor test (CPT) as conditioning stimulus (CS) in healthy individuals (ICC 0.64, 95% CI 0.45-0.77), and pressure as TS with CPT as CS in patients (ICC 0.77, 95% CI 0.70-0.82). The highest inter-session ICC was with IP as TS and IP or CPT as CS (ICC 0.51, 95% CI 0.42-0.59) in healthy subjects. The only data available in patients for inter-session reliability were with pressure as TS and CPT as CS (ICC 0.44, 95% CI 0.11-0.69). Quality ranged from very good to excellent using the QACMRR checklist. The majority of the studies (24 out of 25) scored inadequate in Kappa coefficient reporting item of the COSMIN-ROB checklist.

CONCLUSIONS

Pressure and CPT were the TS and CS most consistently associated with good to excellent intra-session reliability in healthy volunteers and chronic pain patients. The inter-session reliability was fair or less for all modalities, both in healthy volunteers and chronic pain patients.

Therapeutic Patient Education for Fibromyalgia during Spa Therapy: The FiETT Randomized Controlled Trial

Spa therapy is known to improve quality of life and diminish pain. We assessed the efficacy (Fibromyalgia Impact Questionnaire-FIQ) and safety at 6 months of a fibromyalgia-specific therapeutic patient education (TPE) program added to fibromyalgia-specific standardized spa therapy (SST), compared to SST alone, in a controlled randomized trial. We enrolled 157 patients, mostly women, attending spa centers in Southwest France in 2015–2016, and randomized them to SST + TPE (79) or SST (78). The intention-to-treat with “missing as failure” analysis showed a tendency toward a higher, though non-significant, benefit with TPE than without for FIQ (−9 vs. −3; p = 0.053) or pain intensity (−0.9 vs. −1.1; p = 0.58). In addition, pain relief (+3.2 vs. +4.3; p = 0.03) and fatigue (−1.6 vs. −3.7; p = 0.02) were significantly improved, and 87% patients in the SST + TPE arm still regularly practiced the physical exercises taught to them at 6 months. We suspect significant and lasting improvement from spa therapy, as well as our already well-informed and well-managed participants, to have prevented the demonstration of a significant benefit of TPE on FIQ.

Effects of placebo administration on immune mechanisms and relationships with central endogenous opioid neurotransmission

Behavioral conditioning and expectation can have profound impact on animal and human physiology. Placebo, administered under positive expectation in clinical trials, can have potent effects on disease pathology, obscuring active medications. Emerging evidence suggests placebo-responsive neurotransmitter systems (e.g., endogenous opioid) regulate immune function by manipulating inflammatory proteins including IL-18, a potent pro-inflammatory, nociceptive cytokine implicated in pathophysiology of various diseases. Validation that neuroimmune interactions involving brain μ-opioid receptor (MOR) activity and plasma IL-18 underlie placebo analgesic expectation could have widespread clinical applications. Unfortunately, current lack of mechanistic clarity obfuscates clinical translation. To elucidate neuroimmune interactions underlying placebo analgesia, we exposed 37 healthy human volunteers to a standardized pain challenge on each of 2 days within a Positron Emission Tomography (PET) neuroimaging paradigm using the MOR selective radiotracer, ¹¹C-Carfentanil (CFN). Each day volunteers received an intervention (placebo under analgesic expectation or no treatment), completed PET scanning, and rated their pain experience. MOR BP_ND parametric maps were generated from PET scans using standard methods. Results showed placebo reduced plasma IL-18 during pain (W₇₄ = -3.7, p < 0.001), the extent correlating with reduction in pain scores. Placebo reduction in IL-18 covaried with placebo-induced endogenous opioid release in the left nucleus accumbens (T₁₄₈ = 3.33; p_uncorr < 0.001) and left amygdala (T₁₄₈ = 3.30; p_uncorr < 0.001). These findings are consistent with a modulating effect of placebo (under analgesic expectation in humans) on a potent nociceptive, pro-inflammatory cytokine (IL-18) and underlying relationships with endogenous opioid activity, a neurotransmitter system critically involved in pain, stress, and mood regulation.

Influence of Catechol-O-Methyltransferase Gene Polymorphism on the Correlation between Alexithymia and Hypervigilance to Pain

The psychological characteristic of having difficulty expressing emotions, known as alexithymia, is associated with hypervigilance to pain and is considered one of the risk factors for chronic pain. The correlation between alexithymia and hypervigilance to pain can be observed even in healthy individuals. However, the factors influencing this correlation remain unknown. We explored the dopamine system, which is known to be involved in emotion and pain. The dopamine-degrading enzyme catechol-O-methyltransferase (COMT) has a genetic polymorphism known to influence dopamine metabolism in the prefrontal cortex. COMT polymorphism reportedly affects various aspects of pain and increases pain sensitivity in Met allele carriers. Therefore, we investigated whether the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism in healthy individuals. The results revealed a significant positive correlation between the "difficulty describing feelings" of the 20-item Toronto Alexithymia Scale and the "attention to changes in pain" of the pain vigilance and awareness questionnaire in COMT Met carriers but not in Val/Val individuals. This finding suggests that the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism.

Interplay between genetics and lifestyle on pain susceptibility in women with fibromyalgia: The al-Ándalus project

Objectives

It is widely acknowledged that the experience of pain is promoted by both genetic susceptibility and environmental factors such as engaging in physical activity (PA), and that pain-related cognitions are also important. Thus, the purpose of the present study was to test the association of 64 polymorphisms (34 candidate genes) and the gene–gene, gene–PA and gene–sedentary behaviour interactions with pain and pain-related cognitions in women with FM.

Methods

Saliva samples from 274 women with FM [mean (s.d.) age 51.7 (7.7) years] were collected for extracting DNA. We measured PA and sedentary behaviour by accelerometers for a week, pain with algometry and questionnaires, and pain-related cognitions with questionnaires. To assess the robustness of the results, a meta-analysis was also performed.

Results

The rs6311 and rs6313 polymorphisms (5-hydroxytryptamine receptor 2A, HTR2A) were individually related to algometer scores. The interaction of rs4818 (catechol-O-methyltransferase, COMT) and rs1799971 (opioid receptor μ gene, OPRM1) was related to pain catastrophizing. Five gene–behaviour interactions were significant: the interactions of sedentary behaviour with rs1383914 (adrenoceptor alpha 1A, ADRA1A), rs6860 (charged multivesicular body protein 1A, CHMP1A), rs4680 (COMT), rs165599 (COMT) and rs12994338 (SCN9A) on bodily pain subscale of the Short Form 36. Furthermore, the meta-analysis showed an association between rs4680 (COMT) and severity of FM symptoms (codominant model, P-value 0.032).

Conclusion

The HTR2A gene (individually), COMT and OPRM1 gene–gene interaction, and the interactions of sedentary behaviour with ADRA1A, CHMP1A, COMT and SCN9A genes were associated with pain-related outcomes. Collectively, findings from the present study indicate a modest contribution of genetics and gene–sedentary behaviour interaction to pain and pain catastrophizing in women with FM. Future research should examine whether reducing sedentary behaviour is particularly beneficial for reducing pain in women with genetic susceptibility to pain.

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.

Reviewing pharmacogenetics to advance precision medicine for opioids

BACKGROUND

Adequate opioid prescribing is critical for therapeutic success of pain management. Despite the widespread use of opioids, optimized opioid therapy remains unresolved with risk of accidental lethal overdosing. With the emergence of accumulating evidence linking genetic variation to opioid response, pharmacogenetic based treatment recommendations have been proposed.

OBJECTIVE

The aim of this review is to evaluate pharmacogenetic evidence and provide an overview on genes involved in the pharmacokinetics and pharmacodynamics of opioids.

METHODS

For this review, a systematic literature search of published articles was used in PubMed®, with no language restriction and between the time period of January 2000 to December 2020. We reviewed randomized clinical studies, study cohorts and case reports that investigated the influence of genetic variants on selected opioid pharmacokinetics and pharmacodynamics. In addition, we reviewed current CPIC clinical recommendations for pharmacogenetic testing.

RESULTS

Results of this review indicate consistent evidence supporting the association between selected genetic variants of CYP2D6 for opioid metabolism. CPIC guidelines include recommendations that indicate the avoidance of tramadol use, in addition to codeine, in CYP2D6 poor metabolizers and ultrarapid metabolizers, and to monitor intermediate metabolizers for less-than-optimal response. While there is consistent evidence for OPRM1 suggesting increased postoperative morphine dosing requirements in A118G G-allele carriers, the clinical relevance remains limited.

CONCLUSION

There is emerging evidence of clinical relevance of CYP2D6 and, to a lesser extent, OPRM1 polymorphism in personalized opioid drug dosing. As a result, first clinics have started to implement pharmacogenetic guidelines for CYP2D6 and codeine.

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.

Endogenous and iatrogenic sources of variability in response to opioid therapy in Post-Surgical and injured orthopedic patients

BACKGROUND

Hydrocodone is the most prescribed opioid in the US. The objective was to evaluate associations between genetic, intrinsic, and extrinsic patient factors, plasma hydrocodone and metabolites, common side effects, and pain scores in a cohort of orthopedic surgery patients.

METHODS

Data for each patient was collected by review of the electronic hospital record (EHR), and patient interview. Patients were recruited from those with trauma or undergoing scheduled elective surgery for total knee replacement or total hip at the University of Louisville Hospital, Baptist East Hospital, and Jewish Hospital, Louisville, KY. Plasma opiate concentrations and a targeted genotyping panel was performed.

RESULTS

There were statistically significant correlations with daily (p < 0.001) and total dose (p = 0.002) of hydrocodone in hospital and duration of opioid therapy. The length of opioid administration was significantly shorter in CYP2D6 EM/UM versus CYP2D6 PM/IM patients (p = 0.018). Subjects with the OPRM1 c.118G variant were also on opioids longer (p = 0.022). The effect of co-administration of a CYP2D6 inhibitor had a significant effect on the length of opioid therapy (P < 0.001). And not surprisingly the effect of the inhibitor adjusted CYP2D6 phenotype was greater in both the hospital stay period and days of opioid use post hospital discharge (p < 0.001).

CONCLUSIONS

Based on this study, patients should be evaluated for the use of inhibitors of CYP2D6, during hydrocodone therapy can alter the phenotype of the patient (phenocopy) and increase the probability that the patient will be on opioids for longer periods of time.

The roles of borderline personality disorder symptoms and dispositional capability for suicide in suicidal ideation and suicide attempts: Examination of the COMT Val158Met polymorphism

There is a need to identify the subset of individuals with borderline personality disorder (BPD) symptoms at greatest risk for transitioning from suicidal ideation to a suicide attempt. Contemporary models of suicide risk propose that the capability for suicide is necessary for moving from suicidal ideation to a suicide attempt. Few studies have examined dispositional capability factors for suicide, especially among individuals with BPD symptoms. One candidate may be the catechol-o-methyltransferase (COMT) Val158Met polymorphism given its influence on pain sensitivity and fear. This study examined the interactive relation of BPD symptoms and the COMT Val158Met polymorphism to suicidal ideation and suicide attempts. Fifty-nine treatment-seeking patients were recruited. Participants were administered a series of clinical interviews to evaluate BPD symptoms and suicidal thoughts and behaviors. Saliva samples were collected for genotyping. The relation between BPD symptoms and suicidal ideation was not influenced by the Val158Met polymorphism. However, among Val/Val carriers, the probability of a lifetime suicide attempt increased as BPD symptom severity increased. Findings provide preliminary support for the Val/Val variant as a dispositional factor that may increase risk for suicide attempts in BPD; however, results must be interpreted with caution until replication of findings occurs in larger samples.

Genetic Influence on Nociceptive Processing in the Human Brain-A Twin Study

Nociceptive processing in the human brain is complex and involves several brain structures and varies across individuals. Determining the structures that contribute to interindividual differences in nociceptive processing is likely to improve our understanding of why some individuals feel more pain than others. Here, we found specific parts of the cerebral response to nociception that are under genetic influence by employing a classic twin-design. We found genetic influences on nociceptive processing in the midcingulate cortex and bilateral posterior insula. In addition to brain activations, we found genetic contributions to large-scale functional connectivity (FC) during nociceptive processing. We conclude that additive genetics influence specific brain regions involved in nociceptive processing. The genetic influence on FC during nociceptive processing is not limited to core nociceptive brain regions, such as the dorsal posterior insula and somatosensory areas, but also involves cognitive and affective brain circuitry. These findings improve our understanding of human pain perception and increases chances to find new treatments for clinical pain.

A cross-sectional study of breast pain in a diverse population of breast cancer patients

BACKGROUND

Breast cancer is the most common cancer in women, and postoperative breast pain has been reported to be anywhere from 25% to 60%. However, there is sparse data regarding racial/ethnic differences in breast pain among breast cancer patients.

METHODS

We performed a cross-sectional anonymous survey of breast cancer patients from the Hawaii Cancer Consortium over a 6-week period between 2019 and 2020. The 237 breast cancer participants were ages 29 to 98, 74% Asian, and mainly from outpatient oncology clinics. We evaluated the prevalence of breast pain in a diverse group of breast cancer patients and characterized the pain using a modified short-form McGill pain questionnaire (sfMPQ).

RESULTS

Eighty-fourrespondents(35.4%) reported breast pain. On univariable analysis, we found significant racial/ethnic differences in the amount of breast pain, where Chinese and Japanese participants reported significantly less pain compared to White participants on a 10-point pain scale. We found differences in breast pain according to age and endocrine therapy use as well as survey location, however, no differences were seen according to chemotherapy, radiation, or breast surgery. Based on the sfMPQ, the most common descriptors of breast pain were sensory (throbbing, shooting, and stabbing) compared to affective (tiring-exhausting, sickening, fearful, and punishing-cruel) characteristics. Although they were described as mild and intermittent, in women with breast pain, 33.4% reported the breast pain affected their sleep, 16.7% their work, and 15.4% their sexual activity.

CONCLUSIONS

Breast pain is a significant problem in our breast cancer community. This survey assessment has informed our understanding of breast pain in our diverse population. In turn, we are developing culturally appropriate pain management strategies to treat this challenging symptom common in breast cancer survivors.

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.

Aberrant Brain Signal Variability and COMT Genotype in Chronic TMD Patients

The analysis of brain signal variability is a promising approach to understand pathological brain function related to chronic pain. This study investigates whether blood-oxygen-level-dependent signal variability (BOLD_SV) in specific frequency bands is altered in temporomandibular disorder (TMD) and correlated to its clinical features. Twelve patients with chronic myofascial TMD and 24 healthy controls (HCs) underwent resting-state functional magnetic resonance imaging. The BOLD_SV was measured as the standard deviation of the BOLD time series at each voxel and compared between groups. We also examined the potential relationship between the BOLD_SV and the catechol-O-methyltransferase (COMT) Val¹⁵⁸Met polymorphism. We assessed sensory-discriminative pain in the craniofacial region, pain sensitivity to sustained masseteric pain challenge, and TMD pain frequency for clinical correlation. Patients displayed reduced BOLD_SV in the dorsolateral prefrontal cortex (dlPFC) as compared with HC in all frequency bands. In the slow-3 band, patients also showed reduced BOLD_SV in the medial dorsal thalamus, primary motor cortex (M1), and primary somatosensory cortex (S1) and heightened BOLD_SV in the temporal pole. Notably, we found a significant correlation between lower BOLD_SV (slow-3) in the orofacial M1/S1 regions and higher clinical pain (intensity/area) and higher sensitivity of the masseter muscle pain. Moreover, lower BOLD_SV (slow-3) in the dlPFC and ventrolateral PFC was associated with a higher TMD pain frequency. Participants who had the COMT ¹⁵⁸Met substitution exhibited lower BOLD_SV in the dlPFC and higher BOLD_SV in the temporal pole as compared with participants without the COMT ¹⁵⁸Met substitution. An increasing number of Met alleles was associated with lower dlPFC and greater temporal pole BOLD_SV in both HC and TMD groups. Together, we demonstrated that chronic TMD patients exhibit aberrant BOLD_SV in the top-down pain modulatory and sensorimotor circuits associated with their pain frequency and severity. COMT Val¹⁵⁸Met polymorphism might affect clinical symptoms in association with regional brain signal variability, specifically involved in cognitive and emotional regulation of pain.

Baroreceptor Modulation of the Cardiovascular System, Pain, Consciousness, and Cognition

Baroreceptors are mechanosensitive elements of the peripheral nervous system that maintain cardiovascular homeostasis by coordinating the responses to external and internal environmental stressors. While it is well known that carotid and cardiopulmonary baroreceptors modulate sympathetic vasomotor and parasympathetic cardiac neural autonomic drive, to avoid excessive fluctuations in vascular tone and maintain intravascular volume, there is increasing recognition that baroreceptors also modulate a wide range of non-cardiovascular physiological responses via projections from the nucleus of the solitary tract to regions of the central nervous system, including the spinal cord. These projections regulate pain perception, sleep, consciousness, and cognition. In this article, we summarize the physiology of baroreceptor pathways and responses to baroreceptor activation with an emphasis on the mechanisms influencing cardiovascular function, pain perception, consciousness, and cognition. Understanding baroreceptor-mediated effects on cardiac and extra-cardiac autonomic activities will further our understanding of the pathophysiology of multiple common clinical conditions, such as chronic pain, disorders of consciousness (e.g., abnormalities in sleep-wake), and cognitive impairment, which may result in the identification and implementation of novel treatment modalities. © 2021 American Physiological Society. Compr Physiol 11:1373-1423, 2021.

Low catechol-O-methyltransferase and stress potentiate functional pain and depressive behavior, especially in female mice

Low levels of catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, and stress, which potentiates catecholamine release from sympathetic nerves, are fundamental to chronic functional pain syndromes and comorbid depression, which predominantly affect females. Here, we sought to examine the independent and joint contributions of low COMT and stress to chronic functional pain and depression at the behavioral and molecular level. Male and female C57BL/6 mice received sustained systemic delivery of the COMT inhibitor OR486 over 14 days and underwent a swim stress paradigm on days 8 to 10. Pain and depressive-like behavior were measured over 14 days, and brain-derived neurotrophic factor (BDNF; a factor involved in nociception and depression) and glucocorticoid receptor (GR; a stress-related receptor) expression were measured on day 14. We found that stress potentiates the effect of low COMT on functional pain and low COMT potentiates the effect of stress on depressive-like behavior. The joint effects of low COMT and stress on functional pain and depressive-like behavior were significantly greater in females vs males. Consistent with behavioral data, we found that stress potentiates COMT-dependent increases in spinal BDNF and low COMT potentiates stress-dependent decreases in hippocampal BDNF in females, but not males. Although low COMT increases spinal GR and stress increases hippocampal GR expression, these increases are not potentiated in the OR486 + stress group and are not sex-specific. These results suggest that genetic and environmental factors that enhance catecholamine bioavailability cause abnormalities in BDNF signaling and increase risk of comorbid functional pain and depression, especially among females.

Leadership Style, Headache, and Neck Pain: The Moderating Role of the Catechol-O-Methyltransferase (COMT) Genotype

OBJECTIVE

Leadership styles can influence subordinates' health. We investigated how the gene encoding the Catechol-O-Methyltransferase (COMT) enzyme (ie, COMT rs4680 Val158Met) influenced effects of abusive supervision and transformational leadership on subordinates' headache and neck pain.

METHODS

Multiple group structural equation modeling (SEM) was employed to test associations of leadership with subordinates' pain 6 months after in a representative sample of the Norwegian working population (n = 996). Genotyping was performed by TaqMan technology.

RESULTS

Abusive supervision was associated with increased risk, and transformational leadership with decreased risk, of headache and neck pain. Both leadership styles exhibited more pronounced effects in individuals with the Met/Met genotype.

CONCLUSION

Met/Met employees were relatively vulnerable to adversity, but also relatively responsive to constructive leadership. Many workers may benefit more from constructive leadership than population-averaged associations might suggest.

The association between selected genetic variants and individual differences in experimental pain

OBJECTIVES

The underlying mechanisms for individual differences in experimental pain are not fully understood, but genetic susceptibility is hypothesized to explain some of these differences. In the present study we focus on three genetic variants important for modulating experimental pain related to serotonin (SLC6A4 5-HTTLPR/rs25531 A>G), catecholamine (COMT rs4680 Val158Met) and opioid (OPRM1 rs1799971 A118G) signaling. We aimed to investigate associations between each of the selected genetic variants and individual differences in experimental pain.

METHODS

In total 356 subjects (232 low back pain patients and 124 healthy volunteers) were genotyped and assessed with tests of heat pain threshold, pressure pain thresholds, heat pain tolerance, conditioned pain modulation (CPM), offset analgesia, temporal summation and secondary hyperalgesia. Low back pain patients and healthy volunteers did not differ in regards to experimental test results or allelic frequencies, and were therefore analyzed as one group. The associations were tested using analysis of variance and the Kruskal-Wallis test.

RESULTS

No significant associations were observed between the genetic variants (SLC6A4 5-HTTLPR/rs25531 A>G, COMT rs4680 Val158Met and OPRM1 rs1799971 A118G) and individual differences in experimental pain (heat pain threshold, pressure pain threshold, heat pain tolerance, CPM, offset analgesia, temporal summation and secondary hyperalgesia).

CONCLUSIONS

The selected pain-associated genetic variants were not associated with individual differences in experimental pain. Genetic variants well known for playing central roles in pain perception failed to explain individual differences in experimental pain in 356 subjects. The finding is an important contribution to the literature, which often consists of studies with lower sample size and one or few experimental pain assessments.

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.