Abstract
Introduction
The perioperative pain experience shows great interindividual variability and is difficult to predict. The mu-1 opioid receptor gene (OPRM1) is known to play an important role in opioid-pain pathways. Since deoxyribonucleic acid (DNA) methylation is a potent repressor of gene expression, DNA methylation was evaluated at the OPRM1 promoter, as a predictor of preoperative, acute, and chronic postsurgical pain (CPSP).
Methods
A prospective observational cohort study was conducted in 133 adolescents with idiopathic scoliosis undergoing spine fusion under standard protocols. Data regarding pain, opioid consumption, anxiety, and catastrophizing (using validated questionnaires) were collected before and 2–3 months postsurgery. Outcomes evaluated were preoperative pain, acute postoperative pain (area under curve [AUC] for pain scores over 48 hours), and CPSP (numerical rating scale >3/10 at 2–3 months postsurgery). Blood samples collected preoperatively were analyzed for DNA methylation by pyrosequencing of 22 CpG sites at the OPRM1 gene promoter. The association of each pain outcome with the methylation percentage of each CpG site was assessed using multivariable regression, adjusting for significant (P<0.05) nongenetic variables.
Results
Majority (83%) of the patients reported no pain preoperatively, while CPSP occurred in 36% of the subjects (44/121). Regression on dichotomized preoperative pain outcome showed association with methylation at six CpG sites (1, 3, 4, 9, 11, and 17) (P<0.05). Methylation at CpG sites 4, 17, and 18 was associated with higher AUC after adjusting for opioid consumption and preoperative pain score (P<0.05). After adjusting for postoperative opioid consumption and preoperative pain score, methylation at CpG sites 13 and 22 was associated with CPSP (P<0.05).
Discussion
Novel CPSP biomarkers were identified in an active regulatory region of the OPRM1 gene that binds multiple transcription factors. Inhibition of binding by DNA methylation potentially decreases the OPRM1 gene expression, leading to a decreased response to endogenous and exogenous opioids, and an increased pain experience.
Acknowledgments
The authors would like to acknowledge Ashley Ulm and Veda Yadagiri (Pyrosequencing Core, Cincinnati Children’s Hospital Medical Center [CCHMC]) and Diane Kissell for their role in analyzing the DNA extraction and pyrosequencing, under the supervision of Hong Ji (Director, Pyrosequencing Core) and Kejian Zhang (Director of Molecular Genetics Lab, CCHMC). They would also like to acknowledge Kayla Stallworth and Hope Esslinger, CCRC IV, previous research coordinators for the Department of Anesthesia, CCHMC, for their help with patient recruitment in the earlier stages of the study. This study was supported by 5K23HD082782 through the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health (PI: Chidambaran), Center for Pediatric Genomics, and Shared Facility Discovery Award from CCHMC (PI: Chidambaran). The authors are solely responsible for the content, and it does not necessarily represent the official views of the National Institutes of Health.
Disclosure
The authors report no conflicts of interest in this work.