Effects of Prenatal Opioid Exposure on Methylation of OPRM-1 and Subsequent Neonatal Abstinence Syndrome
Introduction. Neonatal Abstinence Syndrome (NAS) is a collection of symptoms due to drug-withdrawal and presents in infants exposed to opioids in utero, which may result from the use of prescription, illegal, or maintenance drugs, which is currently increasing in incidence.1-2 Neonates are treated for NAS primarily via morphine, methadone, and buprenorphine (at an increasing rate), with the addition of phenobarbital in refractory cases.3 Currently it is unknown what causes large variation in severity of NAS presentation in neonates, this study sought to assess the implications of methylation patterns in the promoter region of the mu opioid receptor gene (OPRM-1).2-4 Several studies have indicated that hypermethylation in specific regions of this gene promoter are associated with increased severity of NAS symptoms.2, 5 Methods. Samples of DNA were obtained from neonates being treated for NAS via cord blood or saliva. These samples were then analyzed for the level of methylation at multiple CpG sites on the OPRM-1 promoter, which were analyzed via bisulfide treatment using EZ DNA Methylation-Gold Kit.2,5 The methylation levels were then correlated with the patient outcomes based on the need for treatment and the number of medications required for adequate treatment (≥2 medications indicating severe NAS).2,5 Treatment was determined via the Finnegan Scoring Scale, which assesses the severity of NAS and guides the pharmacotherapy on the basis of CNS, respiratory and gastrointestinal disturbances.6 Results. There was no significant association found between CpG methylation patterns and the need for NAS treatment. However, hypermethylation at the -10 and -14 CpG sites of the OPRM-1 gene were significant for the need of ≥2 medications.2 An additional study expanded upon these sites and indicated that hypermethylation at the -18 and +23 CpG sites of the OPRM-1 gene are associated with a significant increase in pharmacological treatment.5 Conclusions. Hypermethylation in the OPRM-1 gene promoter was demonstrated to reduce OPRM-1 gene expression, reduce pain tolerance, and subsequent need for opioids in adults with cancer. This study concludes that a similar mechanism is seen in neonates with hypermethylation in the OPRM-1 gene promoter after opioid exposure in utero.5 Both the -10 and -14 CpG sites of the OPRM-1 gene are both located within the Sp1 transcription factor binding site.2 Therefore, hypermethylation of these locations leads to downregulation of the OPRM-1 gene and thus mu opioid receptors, which leads to the requirement of increased pharmacological therapy to treat NAS symptoms in these neonates.2 Understanding of the genetics associated with NAS, specifically epigenetic modifications can yield predictions of neonatal outcome and thus lead to individualized treatment plans, which will likely decrease the healthcare related costs associated with this condition.
- Reddy, U.M., Davis, J.M., Ren, Z. and Greene, M.F., 2017. Opioid use in pregnancy, neonatal abstinence syndrome, and childhood outcomes: executive summary of a joint workshop by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, American College of Obstetricians and Gynecologists, American Academy of Pediatrics, Society for Maternal-Fetal Medicine, Centers for Disease Control and Prevention, and the March of Dimes Foundation. Obstetrics & Gynecology, 130(1), pp.10-28.
- Wachman EM, Hayes MJ, Lester BM, et al. Epigenetic Variation in the Mu-Opioid Receptor Gene in Infants with Neonatal Abstinence Syndrome. The Journal of Pediatrics. 2014;165(3):472-478. doi:10.1016/j.jpeds.2014.05.040.
- Tolia, V.N., Patrick, S.W., Bennett, M.M., Murthy, K., Sousa, J., Smith, P.B., Clark, R.H. and Spitzer, A.R., 2015. Increasing incidence of the neonatal abstinence syndrome in US neonatal ICUs. New England Journal of Medicine, 372(22), pp.2118-2126.
- Wachman EM, Hayes MJ, Sherva R, et al. Variations in opioid receptor genes in neonatal abstinence syndrome. Drug and Alcohol Dependence. 2015;155:253-259. doi:10.1016/j.drugalcdep.2015.07.001.
- Wachman EM, Hayes MJ, Shrestha H, et al. Epigenetic variation in OPRM1 gene in opioid-exposed mother-infant dyads. Genes, Brain and Behavior. 2018. doi:10.1111/gbb.12476.
- Kraft, W.K., Stover, M.W. and Davis, J.M., 2016, April. Neonatal abstinence syndrome: Pharmacologic strategies for the mother and infant. In Seminars in perinatology(Vol. 40, No. 3, pp. 203-212). Elsevier.