Epigenetic variation in the mu-opioid receptor gene in infants with neonatal abstinence syndrome

Effect of prenatal and early post-natal oxycodone exposure on the reinforcing and antinociceptive effects of oxycodone in adult C57BL/6 J mice

Abuse of opioids (mu-opioid agonists such as oxycodone) among parents during the gestation and early post-natal period is a concern for the long-term health of the offspring, beyond potential neonatal withdrawal symptoms. However, there is only limited information on such effects.

OBJECTIVES

We examined how prenatal, and early-post natal oxycodone exposure affected opioid addiction behaviors.

METHODS

Adult male and female C57BL/CJ mice housed separately were first injected with ascending doses of oxycodone 1 time/day (1 mg/kg × 10 days, 1.5 mg/kg × 10 days, 2 mg/kg × 10 days, s.c.) whereas control mice were injected with saline. Newly formed parental dyads were then housed together and continued to receive ascending doses of oxycodone (3 mg/kg × 10 days, 4 mg/kg × 10 days, 5 mg/kg × 10 days, 6 mg/kg × 10 days or saline, s.c.) or saline during mating and gestation until the birth of the litter. The dams continued to receive oxycodone or saline through lactation, until F1 offspring were weaned. Upon reaching adulthood (12 weeks of age), male and female F1 offspring were examined in intravenous self-administration (IVSA) of oxycodone, on oxycodone-induced conditioned place preference (CPP) and oxycodone-induced antinociception.

RESULTS

Adult F1 male and female offspring of parental dyads exposed to oxycodone self-administered more oxycodone, compared to offspring of control parental dyads. Ventral and dorsal striatal mRNA levels of genes such as Fkbp5 and Oprm1 were altered following oxycodone self-administration.

CONCLUSION

Prenatal and early post-natal oxycodone exposure enhanced oxycodone self-administration during adulthood in the C57BL/6 J mice.

Transplacental methadone exposure and risk of Neonatal Opioid Withdrawal Syndrome

STUDY OBJECTIVE

Neonatal opioid withdrawal syndrome (NOWS) is a condition that often occurs in neonates born to mothers who received methadone treatment for opioid use disorder during pregnancy. Early identification and treatment of infants at risk of NOWS may improve clinical outcomes. The purpose of this study was to evaluate whether maternal and umbilical cord plasma concentrations of methadone and its metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), could predict the need for NOWS treatment.

DESIGN

Single-center prospective study.

SETTING

University of Michigan Neonatal Intensive Care Unit.

PATIENTS

The study included 11 opioid-dependent mother-infant dyads, where the mothers were treated with methadone at 34 weeks' gestation or later.

INTERVENTION

Maternal and cord blood samples were collected from the study participants.

MEASUREMENTS AND MAIN RESULTS

Maternal and cord plasma concentrations of methadone and EDDP were determined. Six out of the 11 infants required treatment for NOWS. Maternal methadone plasma concentrations were comparable between infants requiring and not requiring NOWS treatment (329.1 ± 229.7 ng/mL vs. 413.2 ± 329.8 ng/mL). However, the average cord plasma methadone concentration in infants who did not require NOWS treatment was 2.9-fold higher than in those who required the treatment (120.0 ± 88.6 ng/mL vs. 40.9 ± 24.4 ng/mL), although the difference was not statistically significant. The ratios of maternal-to-cord methadone plasma concentrations were significantly higher in patients who required treatment for NOWS compared with those who did not (7.7 ± 1.9 vs. 3.5 ± 1.6, p = 0.003). Maternal and cord plasma EDDP concentrations and the maternal-to-cord plasma EDDP concentration ratios did not differ between patients who required and did not require treatment for NOWS.

CONCLUSIONS

The results suggest that methadone permeability across the blood-placental barrier may affect in utero exposure to methadone, and the maternal-to-cord methadone plasma concentration ratio could be a potential biomarker for predicting the need for NOWS treatment.

Neonatal opioid toxicity: opioid withdrawal (abstinence) syndrome with emphasis on pharmacogenomics and respiratory depression

The increasing use of opioids in pregnant women has led to an alarming rise in the number of cases of neonates with drug-induced withdrawal symptoms known as neonatal opioid withdrawal syndrome (NOWS). NOWS is a toxic heterogeneous condition with many neurologic, autonomic, and gastrointestinal symptoms including poor feeding, irritability, tachycardia, hypertension, respiratory defects, tremors, hyperthermia, and weight loss. Paradoxically, for the management of NOWS, low doses of morphine, methadone, or buprenorphine are administered. NOWS is a polygenic disorder supported by studies of genomic variation in opioid-related genes. Single-nucleotide polymorphisms (SNPs) in CYP2B6 are associated with variations in NOWS infant responses to methadone and SNPs in the OPRM1, ABCB1, and COMT genes are associated with need for treatment and length of hospital stay. Epigenetic gene changes showing higher methylation levels in infants and mothers have been associated with more pharmacologic treatment in the case of newborns, and for mothers, longer infant hospital stays. Respiratory disturbances associated with NOWS are not well characterized. Little is known about the effects of opioids on developing neonatal respiratory control and respiratory distress (RD), a potential problem for survival of the neonate. In a rat model to test the effect of maternal opioids on the developing respiratory network and neonatal breathing, maternal-derived methadone increased apneas and lessened RD in neonates at postnatal (P) days P0 and P1. From P3, breathing normalized with age suggesting reorganization of respiratory rhythm-generating circuits at a time when the preBötC becomes the dominant inspiratory rhythm generator. In medullary slices containing the preBötC, maternal opioid treatment plus exposure to exogenous opioids showed respiratory activity was maintained in younger but not older neonates. Thus, maternal opioids blunt centrally controlled respiratory frequency responses to exogenous opioids in an age-dependent manner. In the absence of maternal opioid treatment, exogenous opioids abolished burst frequencies at all ages. Prenatal opioid exposure in children stunts growth rate and development while studies of behavior and cognitive ability reveal poor performances. In adults, high rates of attention deficit disorder, hyperactivity, substance abuse, and poor performances in intelligence and memory tests have been reported.

An epigenetic synopsis of parental substance use

The rate of substance use is rising, especially among reproductive-age individuals. Emerging evidence suggests that paternal pre-conception and maternal prenatal substance use may alter offspring epigenetic regulation (changes to gene expression without modifying DNA) and outcomes later in life, including neurodevelopment and mental health. However, relatively little is known due to the complexities and limitations of existing studies, making causal interpretations challenging. This review examines the contributions and influence of parental substance use on the gametes and potential transmissibility to the offspring's epigenome as possible areas to target public health warnings and healthcare provider counseling of individuals or couples in the pre-conception and prenatal periods to ultimately mitigate short- and long-term offspring morbidity and mortality.

Annual Research Review: Prenatal opioid exposure - a two-generation approach to conceptualizing neurodevelopmental outcomes

Opioid use during pregnancy impacts the health and well-being of two generations: the pregnant person and the child. The factors that increase risk for opioid use in the adult, as well as those that perpetuate risk for the caregiver and child, oftentimes replicate across generations and may be more likely to affect child neurodevelopment than the opioid exposure itself. In this article, we review the prenatal opioid exposure literature with the perspective that this is not a singular event but an intergenerational cascade of events. We highlight several mechanisms of transmission across generations: biological factors, including genetics and epigenetics and the gut-brain axis; parent-child mechanisms, such as prepregnancy experience of child maltreatment, quality of parenting, infant behaviors, neonatal opioid withdrawal diagnosis, and broader environmental contributors including poverty, violence exposure, stigma, and Child Protective Services involvement. We conclude by describing ways in which intergenerational transmission can be disrupted by early intervention.

Potential problems and solutions of opioid-based treatment in neonatal opioid withdrawal syndrome (NOWS): a scoping review protocol

INTRODUCTION

Rates of neonatal opioid withdrawal syndrome (NOWS) have paralleled the rise of opioid use during pregnancy. While short-term phenotypic symptoms of NOWS are well defined, molecular implications and long-term effects are not well understood. Preferred and first-line of treatment for NOWS includes non-pharmacological interventions; however, more than half of the NOWS neonates will need pharmacologics, with opioids as the primary pharmacological treatment. While effective at reducing symptoms, treating NOWS with opioids is paradoxical given that molecular and long-term developmental consequences with such exposure are unknown. There is a pressing need for a synthesis of current and potential/ novel treatment options for NOWS.

METHODS AND ANALYSIS

Following a published framework, a scoping review will be conducted to evaluate NOWS treatment, including established treatment methods and novel methods that may warrant future research and consideration. Using broad search terms, as well as Medical Subject Headings terms, a comprehensive search of PubMed, Cochrane Library, Google Scholar, CINAHL, Web of Science and Scopus, as well as references of selected literature, will take place, followed by a screening procedure to identify included and excluded articles. Included studies must address NOWS treatment, or opioid withdrawal treatment of any age group, that may or may not have been tested in preclinical or clinical models. Results will summarise the current pharmacological and non-pharmacological treatment methods for NOWS, as well as potential novel treatments with a specific interest in non-opioid pharmacological interventions.

ETHICS AND DISSEMINATION

This scoping review aims to broadly search preclinical and clinical literature as it relates to treatment of NOWS, including potential novel treatments with a specific interest in non-opioid pharmacological interventions. Given that this study does not directly involve human subjects or animal subjects research, Institutional Review Board (IRB) or Institutional Animal Care and Use Committee (IACUC) approval is not required. Results of this scoping review will be disseminated at conferences and submitted for publication in a peer-reviewed journal.

A review of the genomics of neonatal abstinence syndrome

Neonatal abstinence syndrome (NAS) is a constellation of signs of withdrawal occurring after birth following in utero exposure to licit or illicit opioids. Despite significant research and public health efforts, NAS remains challenging to diagnose, predict, and manage due to highly variable expression. Biomarker discovery in the field of NAS is crucial for stratifying risk, allocating resources, monitoring longitudinal outcomes, and identifying novel therapeutics. There is considerable interest in identifying important genetic and epigenetic markers of NAS severity and outcome that can guide medical decision making, research efforts, and public policy. A number of recent studies have suggested that genetic and epigenetic changes are associated with NAS severity, including evidence of neurodevelopmental instability. This review will provide an overview of the role of genetics and epigenetics in short and longer-term NAS outcomes. We will also describe novel research efforts using polygenic risk scores for NAS risk stratification and salivary gene expression to understand neurobehavioral modulation. Finally, emerging research focused on neuroinflammation from prenatal opioid exposure may elucidate novel mechanisms that could lead to development of future novel therapeutics.

Future Newborns with Opioid-Induced Neonatal Abstinence Syndrome (NAS) Could Be Assessed with the Genetic Addiction Risk Severity (GARS) Test and Potentially Treated Using Precision Amino-Acid Enkephalinase Inhibition Therapy (KB220) as a Frontline Modality Instead of Potent Opioids

In this nonsystematic review and opinion, including articles primarily selected from PubMed, we examine the pharmacological and nonpharmacological treatments of neonatal abstinence syndrome (NAS) in order to craft a reasonable opinion to help forge a paradigm shift in the treatment and prevention of primarily opioid-induced NAS. Newborns of individuals who use illicit and licit substances during pregnancy are at risk for withdrawal, also known as NAS. In the US, the reported prevalence of NAS has increased from 4.0 per 1000 hospital births in 2010 to 7.3 per 1000 hospital births in 2017, which is an 82% increase. The management of NAS is varied and involves a combination of nonpharmacologic and pharmacologic therapy. The preferred first-line pharmacological treatment for NAS is opioid therapy, specifically morphine, and the goal is the short-term improvement in NAS symptomatology. Nonpharmacological therapies are individualized and typically focus on general care measures, the newborn-parent/caregiver relationship, the environment, and feeding. When used appropriately, nonpharmacologic therapies can help newborns with NAS avoid or reduce the amount of pharmacologic therapy required and the length of hospitalization. In addition, genetic polymorphisms of the catechol-o-methyltransferase (COMT) and mu-opioid receptor (OPRM1) genes appear to affect the length of stay and the need for pharmacotherapy in newborns with prenatal opioid exposure. Therefore, based on this extensive literature and additional research, this team of coauthors suggests that, in the future, in addition to the current nonpharmacological therapies, patients with opioid-induced NAS should undergo genetic assessment (i.e., the genetic addiction risk severity (GARS) test), which can subsequently be used to guide DNA-directed precision amino-acid enkephalinase inhibition (KB220) therapy as a frontline modality instead of potent opioids.

Perinatal Morphine Exposure Leads to Sex-Dependent Executive Function Deficits and Microglial Changes in Mice

Children exposed prenatally to opioids are at an increased risk for behavioral problems and executive function deficits. The prefrontal cortex (PFC) and amygdala (AMG) regulate executive function and social behavior and are sensitive to opioids prenatally. Opioids can bind to toll-like receptor 4 (TLR4) to activate microglia, which may be developmentally important for synaptic pruning. Therefore, we tested the effects of perinatal morphine exposure on executive function and social behavior in male and female mouse offspring, along with microglial-related and synaptic-related outcomes. Dams were injected once daily subcutaneously with saline (n = 8) or morphine (MO; 10 mg/kg; n = 12) throughout pregestation, gestation, and lactation until offspring were weaned on postnatal day 21 (P21). Male MO offspring had impairments in attention and accuracy in the five-choice serial reaction time task, while female MO offspring were less affected. Targeted gene expression analysis at P21 in the PFC identified alterations in microglial-related and TLR4-related genes, while immunohistochemical analysis in adult brains indicated decreased microglial Iba1 and phagocytic CD68 proteins in the PFC and AMG in males, but females had an increase. Further, both male and female MO offspring had increased social preference. Overall, these data demonstrate male vulnerability to executive function deficits in response to perinatal opioid exposure and evidence for disruptions in neuron-microglial signaling.

Effect of Prenatal Opioid Exposure on the Human Placental Methylome

Prenatal exposure to addictive drugs can lead to placental epigenetic modifications, but a methylome-wide evaluation of placental DNA methylation changes after prenatal opioid exposure has not yet been performed. Placental tissue samples were collected at delivery from 19 opioid-exposed and 20 unexposed control full-term pregnancies. Placental DNA methylomes were profiled using the Illumina Infinium HumanMethylationEPIC BeadChip. Differentially methylated CpG sites associated with opioid exposure were identified with a linear model using the ‘limma’ R package. To identify differentially methylated regions (DMRs) spanning multiple CpG sites, the ‘DMRcate’ R package was used. The functions of genes mapped by differentially methylated CpG sites and DMRs were further annotated using Enrichr. Differentially methylated CpGs (n = 684, unadjusted p < 0.005 and |∆β| ≥ 0.05) were mapped to 258 genes (including PLD1, MGAM, and ALCS2). Differentially methylated regions (n = 199) were located in 174 genes (including KCNMA1). Enrichment analysis of the top differentially methylated CpG sites and regions indicated disrupted epigenetic regulation of genes involved in synaptic structure, chemical synaptic transmission, and nervous system development. Our findings imply that placental epigenetic changes due to prenatal opioid exposure could result in placental dysfunction, leading to abnormal fetal brain development and the symptoms of opioid withdrawal in neonates.

Prenatal opioid-exposed infant extracellular miRNA signature obtained at birth predicts severity of neonatal opioid withdrawal syndrome

Prenatal opioid exposure (POE) is commonly associated with neonatal opioid withdrawal syndrome (NOWS), which is characterized by a broad variability in symptoms and severity. Currently there are no diagnostic tools to reliably predict which infants will develop severe NOWS, while risk stratification would allow for proactive decisions about appropriate clinical monitoring and interventions. The aim of this prospective cohort study was to assess if extracellular microRNAs (miRNAs) in umbilical cord plasma of infants with POE could predict NOWS severity. Participants (n = 58) consisted of pregnant women receiving medications for opioid use disorder and their infants. NOWS severity was operationalized as the need for pharmacologic treatment and prolonged hospitalization (≥ 14 days). Cord blood miRNAs were assessed using semi-quantitative qRT-PCR arrays. Receiver operating characteristic curves and area under the curve (AUC) were estimated. The expression of three miRNAs (miR-128-3p, miR-30c-5p, miR-421) predicted need for pharmacologic treatment (AUC: 0.85) and prolonged hospitalization (AUC: 0.90). Predictive validity improved after two miRNAs (let-7d-5p, miR-584-5p) were added to the need for pharmacologic treatment model (AUC: 0.94) and another two miRNAs (let-7b-5p, miR-10-5p) to the prolonged hospitalization model (AUC: 0.99). Infant cord blood extracellular miRNAs can proactively identify opioid-exposed neonates at high-risk for developing severe NOWS.

Effects of Pharmacologic Treatment for Neonatal Abstinence Syndrome on DNA Methylation and Neurobehavior: A Prospective Cohort Study

OBJECTIVE

To determine whether pharmacologic treatment for neonatal abstinence syndrome (NAS) is associated with changes in DNA methylation (DNAm) of the mu-opioid receptor gene (OPRM1) and improvements in neonatal neurobehavior.

STUDY DESIGN

Buccal swabs were collected from 37 neonates before and after morphine treatment for NAS. Genomic DNA was extracted, and DNAm was examined at 4 cytosine-phosphate-guanine (CpG) sites within the OPRM1 gene. Assessment with the NICU Network Neurobehavioral Scales (NNNS) was also performed before and after NAS treatment. Changes in DNAm (DNAm_post-tx - DNAm_pre-tx) and NNNS summary scores (NNNS_post-tx - NNNS_pre-tx) were then calculated. Path analysis was used to examine associations among pharmacologic treatment (length of treatment [LOT] and total dose of morphine), changes in DNAm, and changes in NNNS summary scores.

RESULTS

DNAm was significantly decreased from pretreatment to post-treatment at 1 of 4 CpG sites within the OPRM1 gene. Neonates also demonstrated decreased excitability, hypertonia, lethargy, signs of stress and abstinence, and increased quality of movement and regulation from pretreatment to post-treatment. Longer LOT and higher morphine dose were associated with greater decreases in DNAm; greater decreases in DNAm were associated with greater decreases in excitability and hypertonia on the NNNS.

CONCLUSIONS

Pharmacologic treatment of NAS is associated with decreased DNAm of the OPRM1 gene and improved neonatal neurobehavior. Epigenetic changes may play a role in these changes in neonatal neurobehavior.

Outcomes associated with the use of medications for opioid use disorder during pregnancy

AIM

To test the effect of the duration of medication for opioid use disorder (MOUD) use during pregnancy on maternal, perinatal and neonatal outcomes.

DESIGN

Retrospective cohort analysis of claims, encounter and pharmacy data.

SETTING

Pennsylvania, USA.

PARTICIPANTS

We analyzed 13 320 pregnancies among 10 741 women with opioid use disorder aged 15-44 years enrolled in Pennsylvania Medicaid between 2009 and 2017.

MEASUREMENTS

We examined five outcomes during pregnancy and for 12 weeks postpartum: (1) overdose, (2) postpartum MOUD continuation, (3) preterm birth (< 37 weeks gestation), (4) term low birth weight (< 2500 g at ≥ 37 weeks) and (5) neonatal abstinence syndrome (NAS). Our primary exposure was the duration (count of weeks) of any MOUD use, including methadone or buprenorphine, during pregnancy.

FINDINGS

Among 13 320 pregnancies, 306 (2.3%) were complicated by an overdose, 1753 (13.2%) resulted in a preterm birth and 6787 (50.9%) continued MOUD postpartum. Among infants, 874 (7.6%) were low birth weight at term and 7706 (57.9%) were diagnosed with NAS. As the duration of MOUD use increased, we found a statistically significant decrease in the rate of overdose and preterm birth, a statistically significant increase in the rate of postpartum MOUD continuation and NAS and a decline in term low birth weight. Specifically, for each additional week of MOUD, the adjusted odds of overdose decreased by 2% [adjusted odds ratio (aOR) = 0.98; 95% confidence interval (CI) = 0.97, 0.99], preterm birth decreased by 1% (aOR = 0.99; 95% CI = 0.99, 1.00), postpartum MOUD continuation increased by 95% (aOR = 1.95; 95% CI = 1.87, 2.04) and NAS increased by 41% (aOR = 1.41; 95% CI = 1.35, 1.47). The odds of term low birth weight did not change (aOR = 1.00; 95% CI = 0.99, 1.00), although the rate declined with a longer duration of MOUD use during pregnancy.

CONCLUSIONS

Longer duration of medication for opioid use disorder use during pregnancy appears to be associated with improved maternal and perinatal outcomes.

Co-occurrence of preconception maternal childhood adversity and opioid use during pregnancy: Implications for offspring brain development

Understanding of the effects of in utero opioid exposure on neurodevelopment is a priority given the recent dramatic increase in opioid use among pregnant individuals. However, opioid abuse does not occur in isolation-pregnant individuals abusing opioids often have a significant history of adverse experiences in childhood, among other co-occurring factors. Understanding the specific pathways in which these frequently co-occurring factors may interact and cumulatively influence offspring brain development in utero represents a priority for future research in this area. We highlight maternal history of childhood adversity (CA) as one such co-occurring factor that is more prevalent among individuals using opioids during pregnancy and which is increasingly shown to affect offspring neurodevelopment through mechanisms beginning in utero. Despite the high incidence of CA history in pregnant individuals using opioids, we understand very little about the effects of comorbid prenatal opioid exposure and maternal CA history on fetal brain development. Here, we first provide an overview of current knowledge regarding effects of opioid exposure and maternal CA on offspring neurodevelopment that may occur during gestation. We then outline potential mechanistic pathways through which these factors might have interactive and cumulative influences on offspring neurodevelopment as a foundation for future research in this area.

An Exploratory Pilot Study of Changes in Global DNA Methylation in Patients Undergoing Major Breast Surgery Under Opioid-Based General Anesthesia

This study aimed to investigate DNA methylation levels in patients undergoing major breast surgery under opioid-based general anesthesia. Blood samples were collected from eleven enrolled patients, before, during and after anesthesia. PBMC were isolated and global DNA methylation levels as well as DNA methyltransferase (DNMT) and cytokine gene expression were assessed. DNA methylation levels significantly declined by 26%, reversing the direction after the end of surgery. Likewise, DNMT1a mRNA expression was significantly reduced at all time points, with lowest level of −68%. DNMT3a and DNMT3b decreased by 65 and 71%, respectively. Inflammatory cytokines IL6 and TNFα mRNA levels showed a trend for increased expression at early time-points to end with a significant decrease at 48 h after surgery. This exploratory study revealed for the first time intraoperative global DNA hypomethylation in patients undergoing major breast surgery under general anesthesia with fentanyl. The alterations of global DNA methylation here observed seem to be in agreement with DNMTs gene expression changes. Furthermore, based on perioperative variations of IL6 and TNFα gene expression, we hypothesize that DNA hypomethylation may occur as a response to surgical stress rather than to opiate exposure.

Epigenetic Alterations in Prescription Opioid Misuse: New Strategies for Precision Pain Management

Prescription opioids are used for some chronic pain conditions. However, generally, long-term therapy has unwanted side effects which may trigger addiction, overdose, and eventually cause deaths. Opioid addiction and chronic pain conditions have both been associated with evidence of genetic and epigenetic alterations. Despite intense research interest, many questions about the contribution of epigenetic changes to this typology of addiction vulnerability and development remain unanswered. The aim of this review was to summarize the epigenetic modifications detected in specific tissues or brain areas and associated with opioid prescription and misuse in patients who have initiated prescribed opioid management for chronic non-cancer pain. The review considers the effects of opioid exposure on the epigenome in central and peripheral tissues in animal models and human subjects and highlights the mechanisms in which opioid epigenetics may be involved. This will improve our current understanding, provide the basis for targeted, personalized pain management, and thus balance opioid risks and benefits in managing chronic pain.

Escaping the Finnegan - Is it time?

Neonatal Abstinence Syndrome (NAS) has significantly increased worldwide secondary to a marked increase in the incidence of opioid use disorders (OUD) in women of childbearing age. Since first described in 1975, the Finnegan Neonatal Abstinence Scoring Tool (FNAST) remains the mainstay of monitoring NAS severity and its clinical management. The complexity of the tool (21 independent variables), the need for external validation, excessive subjectivity, poor inter-rater reliability, and uncertainty regarding the clinical relevance of some items has resulted in the need to develop an alternate scoring tool. A validated, simple, clinically relevant, and universally accepted approach to assessing opioid exposed neonates would facilitate high quality clinical care while assisting in the generation of generalizable data from future research studies conducted in this vulnerable population.

Clinical care of neonates undergoing opioid withdrawal in the immediate postpartum period

As the opioid epidemic escalates in westernized countries around the world, chronic opioid use during pregnancy has become a growing public health issue. There are increasing concerns that chronic maternal opioid use might adversely affect the developing fetal brain. Furthermore, the sudden discontinuation of the trans-placental opioid supply at birth puts newborns at acute risk for neonatal opioid withdrawal syndrome (NOWS). NOWS is a multi-system disorder that has been identified in approximately 50-80% of neonates exposed to opioids due to chronic maternal use. Clinically, NOWS affects the central and autonomic nervous systems as well as the gastrointestinal and respiratory tracts. The clinical features of NOWS include hyperirritability, high-pitched crying, restlessness, tremors, poor sleep, agitation, seizures, sweating, fever, poor feeding, regurgitation, diarrhea, and tachypnea. NOWS is currently diagnosed using a clinical scoring tool followed by toxicological confirmation of the presence of opioids in meconium or tissue specimens. The first-line treatments for NOWS are non-pharmacologic comfort measures. If these measures fail, neonates may be treated with opioids and/or sedatives. Since the severity of NOWS can be highly variable, it is quite difficult to predict which opioid-exposed neonates will require pharmacotherapy and prolonged hospitalization. Factors associated with maternal polysubstance use, including the use of illicit substances and tobacco, have been associated with the increased severity and duration of NOWS. Since neonates with NOWS are at increased risk for long-term adverse neurodevelopmental outcomes, ongoing monitoring beyond the neonatal period is essential.

The Life Cycle of the Mu-Opioid Receptor

Opioid receptors (ORs) are undisputed targets for the treatment of pain. Unfortunately, targeting these receptors therapeutically poses significant challenges including addiction, dependence, tolerance, and the appearance of side effects, such as respiratory depression and constipation. Moreover, misuse of prescription and illicit narcotics has resulted in the current opioid crisis. The mu-opioid receptor (MOR) is the cellular mediator of the effects of most commonly used opioids, and is a prototypical G protein-coupled receptor (GPCR) where new pharmacological, signalling and cell biology concepts have been coined. This review summarises the knowledge of the life cycle of this therapeutic target, including its biogenesis, trafficking to and from the plasma membrane, and how the regulation of these processes impacts its function and is related to pathophysiological conditions.

Placental OPRM1 DNA methylation and associations with neonatal opioid withdrawal syndrome, a pilot study

Aims:

Epigenetic variation of DNA methylation of the mu-opioid receptor gene (OPRM1) has been identified in the blood and saliva of individuals with opioid use disorder (OUD) and infants with neonatal opioid withdrawal syndrome (NOWS). It is unknown whether epigenetic variation in OPRM1 exists within placental tissue in women with OUD and whether it is associated with NOWS outcomes. In this pilot study, the authors aimed to 1) examine the association between placental OPRM1 DNA methylation levels and NOWS outcomes, and 2) compare OPRM1 methylation levels in opioid-exposed versus non-exposed control placentas.

Methods:

Placental tissue was collected from eligible opioid (n = 64) and control (n = 29) women after delivery. Placental DNA was isolated and methylation levels at six cytosine-phosphate-guanine (CpG) sites within the OPRM1 promoter were quantified. Methylation levels were evaluated for associations with infant NOWS outcome measures: need for pharmacologic treatment, length of hospital stay (LOS), morphine treatment days, and treatment with two medications. Regression models were created and adjusted for clinical co-variates. Methylation levels between opioid and controls placentas were also compared.

Results:

The primary opioid exposures were methadone and buprenorphine. Forty-nine (76.6%) of the opioid-exposed infants required pharmacologic treatment, 10 (15.6%) two medications, and average LOS for all opioid-exposed infants was 16.5 (standard deviation 9.7) days. There were no significant associations between OPRM1 DNA methylation levels in the six CpG sites and any NOWS outcome measures. No significant differences were found in methylation levels between the opioid and control samples.

Conclusions:

No significant associations were found between OPRM1 placental DNA methylation levels and NOWS severity in this pilot cohort. In addition, no significant differences were seen in OPRM1 methylation in opioid versus control placentas. Future association studies examining methylation levels on a genome-wide level are warranted.

Placental DNA methylation profiles in opioid-exposed pregnancies and associations with the neonatal opioid withdrawal syndrome

Opioid abuse during pregnancy can result in Neonatal Opioid Withdrawal Syndrome (NOWS). We investigated genome-wide methylation analyses of 96 placental tissue samples, including 32 prenatally opioid-exposed infants with NOWS who needed therapy (+Opioids/+NOWS), 32 prenatally opioid-exposed infants with NOWS who did not require treatment (+Opioids/-NOWS), and 32 prenatally unexposed controls (-Opioids/-NOWS, control). Statistics, bioinformatics, Artificial Intelligence (AI), including Deep Learning (DL), and Ingenuity Pathway Analyses (IPA) were performed. We identified 17 dysregulated pathways thought to be important in the pathophysiology of NOWS and reported accurate AI prediction of NOWS diagnoses. The DL had an AUC (95% CI) =0.98 (0.95-1.0) with a sensitivity and specificity of 100% for distinguishing NOWS from the +Opioids/-NOWS group and AUCs (95% CI) =1.00 (1.0-1.0) with a sensitivity and specificity of 100% for distinguishing NOWS versus control and + Opioids/-NOWS group versus controls. This study provides strong evidence of methylation dysregulation of placental tissue in NOWS development.

Maternal and iatrogenic neonatal opioid withdrawal syndrome: Differences and similarities in recognition, management, and consequences

Opioids are potent analgesics used to manage pain in both young and old, but the increased use in the pregnant population has significant individual and societal implications. Infants dependent on opioids, either through maternal or iatrogenic exposure, undergo neonatal opioid withdrawal syndrome (NOWS), where they may experience withdrawal symptoms ranging from mild to severe. We present a detailed and original review of NOWS caused by maternal opioid exposure (mNOWS) and iatrogenic opioid intake (iNOWS). While these two entities have been assessed entirely separately, recognition and treatment of the clinical manifestations of NOWS overlap. Neonatal risk factors such as age, genetic predisposition, drug type, and clinical factors like type of opioid, cumulative dose of opioid exposure, and disease status affect the incidence of both mNOWS and iNOWS, as well as their severity. Recognition of withdrawal is dependent on clinical assessment of symptoms, and the use of clinical assessment tools designed to determine the need for pharmacotherapy. Treatment of NOWS relies on a combination of non-pharmacological therapies and pharmacological options. Long-term consequences of opioids and NOWS continue to generate controversy, with some evidence of anatomic brain changes, but conflicting animal and human clinical evidence of significant cognitive or behavioral impacts on school-age children. We highlight the current knowledge on clinically relevant recognition, treatment, and consequences of NOWS, and identify new advances in clinical management of the neonate. This review brings a unique clinical perspective and critically analyzes gaps between the clinical problem and our preclinical understanding of NOWS.

Clinical pharmacology and dosing regimen optimization of neonatal opioid withdrawal syndrome treatments

In this paper, we review the management of neonatal opioid withdrawal syndrome (NOWS) and clinical pharmacology of primary treatment agents in NOWS, including morphine, methadone, buprenorphine, clonidine, and phenobarbital. Pharmacologic treatment strategies in NOWS have been mostly empirical, and heterogeneity in dosing regimens adds to the difficulty of extrapolating study results to broader patient populations. As population pharmacokinetics (PKs) of pharmacologic agents in NOWS become more well‐defined and knowledge of patient‐specific factors affecting treatment outcomes continue to accumulate, PK/pharmacodynamic modeling and simulation will be powerful tools to aid the design of optimal dosing regimens at the patient level. Although there is an increasing number of clinical trials on the comparative efficacy of treatment agents in NOWS, here, we also draw attention to the importance of optimizing the dosing regimen, which can be arguably equally important at identifying the optimal treatment agent.

Neonatal Opioid Withdrawal Syndrome (NOWS): A Transgenerational Echo of the Opioid Crisis

The incidence of neonatal opioid withdrawal syndrome (NOWS) has increased substantially in the setting of the opioid epidemic, a major public health problem in the United States. At present, NOWS has commonly used assessment and treatment protocols, but new protocols have questioned old practices. However, because of limited access to opioid use disorder (OUD) treatment and socioeconomic factors, many pregnant (and postpartum) women with OUD do not receive treatment. The pathophysiology of NOWS is not completely understood, although limited research studies have been conducted in humans and animals to better understand its etiology. Moreover, there is evidence that epigenetic and genetic factors play a role in the development of NOWS, but further study is needed. Animal models have suggested that there are deleterious effects of in utero opioid exposure later in life. Clinical research has revealed the harmful long-term sequelae of NOWS, with respect to cognitive function and childhood development. Many psychiatric disorders begin during adolescence, so as infants born with NOWS approach adolescence, additional clinical and molecular studies are warranted to identify biologic and psychosocial risk factors and long-term effects of NOWS. Additionally, access to specialized OUD treatment for pregnant women must be more readily available in the United States, especially in rural areas.

Neonatal Abstinence Syndrome Severity Index Predicts 18-Month Neurodevelopmental Outcome in Neonates Randomized to Morphine or Methadone

OBJECTIVE

To develop an index to determine which opioid-exposed neonates have the most severe neonatal abstinence syndrome (NAS).

STUDY DESIGN

Full-term neonates with NAS (n = 116) from mothers maintained on methadone or buprenorphine were enrolled from 8 sites into a randomized clinical trial of morphine vs methadone. Ninety-nine (85%) were evaluated at hospital discharge using the NICU Network Neurobehavioral Scale (NNNS). At 18 months, 83 of 99 (83.8%) were evaluated with the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III), and 77 of 99 (77.7%) were evaluated with the Child Behavior Checklist (CBCL).

RESULTS

Cluster analysis was used to define high (n = 21) and low (n = 77) NAS severity. Compared with infants in the low NAS severity cluster, infants in the high NAS severity cluster had a longer length of stay (P < .001), longer length of stay due to NAS (P < .001), longer duration of treatment due to NAS (P < .001), and higher total dose of the study drug (P < .001) and were more likely to have received phenobarbital (P < .001), to have been treated with morphine (P = .020), and to have an atypical NNNS profile (P = .005). The 2 groups did not differ in terms of maximum Finnegan score. At 18 months, in unadjusted analyses, compared with the high-severity cluster, the low-severity cluster had higher scores on the Bayley-III Cognitive (P = .013), Language (P < .001), and Motor (P = .041) composites and less total behavior problems on the CBCL (P = .028). In adjusted analyses, the difference in the Bayley-III Language composite remained (P = .013).

CONCLUSIONS

Presumptive measures of NAS severity can be aggregated to develop an index that predicts developmental outcomes at age 18 months.

Neuroimaging in infants with prenatal opioid exposure: Current evidence, recent developments and targets for future research

Prenatal opioid exposure (POE) has shown to be a risk factor for adverse long-term cognitive and behavioral outcomes in offspring. However, the neural mechanisms of these outcomes remain poorly understood. While preclinical and human studies suggest that these outcomes may be due to opioid-mediated changes in the fetal and early postnatal brain, other maternal, social, and environmental factors are also shown to play a role. Recent neuroimaging studies reveal brain alterations in children with POE. Early neuroimaging and novel methodology could provide an in vivo mechanistic understanding of opioid mediated alterations in developing brain. However, this is an area of ongoing research. In this review we explore recent imaging developments in POE, with emphasis on the neonatal and infant brain, and highlight some of the challenges of imaging the developing brain in this population. We also highlight evidence from animal models and imaging in older children and youth to understand areas where future research may be targeted in infants with POE.

DNA methylation biomarkers of future health outcomes in children

Biomarkers which predict future health outcomes are key to the goals of precision health. Such biomarkers do not have to be involved in the causal pathway of a disease, and their performance is best assessed using statistical tests of clinical performance and evaluation of net health impact. DNA methylation is the most commonly studied epigenetic process and represents a potential biomarker of future health outcomes. We review 25 studies in non-oncological paediatric conditions where DNA methylation biomarkers of future health outcomes are assessed. Whilst a number of positive findings have been described, the body of evidence is severely limited by issues with outcome measures, tissue-specific samples, accounting for sample cell type heterogeneity, lack of appropriate statistical testing, small effect sizes, limited validation, and no assessment of net health impact. Future studies should concentrate on careful study design to overcome these issues, and integration of DNA methylation data with other 'omic', clinical, and environmental data to generate the most clinically useful biomarkers of paediatric disease.

Prenatal drug exposure and neurodevelopmental programming of glucocorticoid signalling

Prenatal neurodevelopment is dependent on precise functioning of multiple signalling pathways in the brain, including those mobilised by glucocorticoids (GC) and endocannabinoids (eCBs). Prenatal exposure to drugs of abuse, including opioids, alcohol, cocaine and cannabis, has been shown to not only impact GC signalling, but also alter functioning of the hypothalamic-pituitary-adrenal (HPA) axis. Such exposures can have long-lasting neurobehavioural consequences, including alterations in the stress response in the offspring. Furthermore, cannabis contains cannabinoids that signal via the eCB pathway, which is linked to some components of GC signalling in the adult brain. Given that GCs are frequently used in pregnancy to prevent complications of prematurity, and also that rates of cannabis use in pregnancy are increasing, the likelihood of foetal co-exposure to these compounds is high and may have additional implications for long-term neurodevelopment. Here, we present a discussion of GC signalling and the HPA axis, as well as the effects of prenatal drug exposure on these pathways and the stress response, and we explore the interactions between GC and EC signalling in the developing brain and potential for neurodevelopmental consequences.

Maternal responsivity and oxytocin in opioid-dependent mothers

Although prenatal opioid exposure and postnatal withdrawal (neonatal abstinence syndrome) are associated with infant neurobehavioral deficits, little is known about the impact of continued maternal opioid treatment in the postnatal period on maternal responsivity and relationship to mother's oxytocin release during dyadic interactions in the Still Face paradigm. Mother and infant dyads (N = 14) were recruited and comprised of mothers on opioid replacement throughout pregnancy and postpartum (opioid-exposed group, n = 7) and a demographically controlled, non-exposed group (n = 7). Salivary oxytocin was collected following 10 min of infant separation before and immediately after a 6-min Still Face paradigm. Oxytocin measures correlated strongly with sensitive and prosocial maternal behaviors in response to infant initiation. Opioid-exposed compared to non-exposed mothers had significantly lower pre-test to post-test rise in salivary oxytocin concentration level as well as fewer sensitive behaviors during the reunion condition of the Still Face paradigm. Maternal opioid dependence during early infancy may impair maternal responsivity and sensitivity through suppression of the oxytocin reflex to infant stimulation.

Methadone versus morphine treatment outcomes in neonatal abstinence syndrome: A meta-analysis

AIM

To determine whether morphine has better outcomes for neonatal abstinence syndrome treatment than methadone.

METHODS

Studies published before 1 January 2019 were identified using the PubMed, Web of Science, Scopus, Cochrane Library and ClinicalTrials.gov databases. The Cochrane Collaboration Risk of Bias Tool was used to assess the risk of bias for randomised clinical trials. In addition, the risk of bias for non-randomised studies was evaluated by a non-randomised studies of interventions tool.

RESULTS

We identified 1020 published studies, and 5 were included in the final analysis. Results showed no significant difference in opioid treatment days (standardised mean difference (SMD) = 0.32, 95% confidence interval (CI) = -0.16, 0.80), length of hospital stay (SMD = -0.33, 95% CI = -1.21, 0.56) and duration of treatment (SMD = -0.83 95% CI = -2.09, 0.43) between morphine or methadone treatment.

CONCLUSIONS

Our meta-analysis of current evidence demonstrated that neonatal abstinence syndrome treatment with morphine was not associated with better outcomes in infants compared with methadone treatment.

Racial association and pharmacotherapy in neonatal opioid withdrawal syndrome

OBJECTIVE

To determine if racial differences are associated with Neonatal Opioid Withdrawal Syndrome (NOWS) severity.

STUDY DESIGN

A 10-year (2008-2017) retrospective cohort of infants ≥35 weeks gestation with prenatal exposure to opioids was included. The primary measure was the need for pharmacotherapy. Multivariable logistic regression and propensity score analysis were performed.

RESULTS

Among 345 infants with NOWS, 111 (32%) were black infants with 70% of them requiring pharmacotherapy as compared with 84% of white infants. Upon adjusting for significant covariates (methadone, benzodiazepine use, and gestational age), black infants were 57% less likely than whites to require pharmacotherapy (Odds ratio: 0.43, 95%CI: 0.22-0.80, p = 0.009). Similar results were observed with propensity score analysis.

CONCLUSIONS

Significant racial disparity observed may be secondary to genetic variations in opioid pharmacogenomics and/or extrinsic factors. Large-scale studies are warranted to include race in predictive models for early pharmacological intervention.

Prenatal Opioid Exposure: Neurodevelopmental Consequences and Future Research Priorities

Neonatal opioid withdrawal syndrome (NOWS) has risen in prevalence from 1.2 per 1000 births in 2000 to 5.8 per 1000 births in 2012. Symptoms in neonates may include high-pitched cry, tremors, feeding difficulty, hypertonia, watery stools, and breathing problems. However, little is known about the neurodevelopmental consequences of prenatal opioid exposure in infancy, early childhood, and middle childhood. Even less is known about the cognitive, behavioral, and academic outcomes of children who develop NOWS. We review the state of the literature on the neurodevelopmental consequences of prenatal opioid exposure with a particular focus on studies in which NOWS outcomes were examined. Aiming to reduce the incidence of prenatal opioid exposure in the near future, we highlight the need for large studies with prospectively recruited participants and longitudinal designs, taking into account confounding factors such as socioeconomic status, institutional variations in care, and maternal use of other substances, to independently assess the full impact of NOWS. As a more immediate solution, we provide an agenda for future research that leverages the National Institutes of Health Environmental Influences on Child Health Outcomes program to address many of the serious methodologic gaps in the literature, and we answer key questions regarding the short- and long-term neurodevelopmental health of children with prenatal opioid exposure.

Cognitive and Behavioral Impact on Children Exposed to Opioids During Pregnancy

The developmental impact of opioid use during pregnancy is a subject of ongoing debate. Short-term neonatal outcomes, such as lower birth weight and neonatal abstinence syndrome, are the most well-recognized outcomes. However, knowledge gaps exist regarding longer-term neurocognitive and mental health outcomes. In this article, we summarize an expert panel discussion that was held in April 2018 by the Substance Abuse and Mental Health Services Administration and attended by national experts in the field of perinatal opioid exposure and its impact on child development. Despite the challenges with research in this area, there is emerging literature revealing an association between neonates exposed to opioids in utero and longer-term adverse neurocognitive, behavioral, and developmental outcomes. Although adverse sequalae may not be apparent in the neonatal period, they may become more salient as children develop and reach preschool and school age. Multiple variables (genetic, environmental, and biological) result in a highly complex picture. The next steps and strategies to support families impacted by opioid use disorder are explored. Model programs are also considered, including integrated care for the child and mother, parenting supports, and augmentations to home visiting.

Maternal hair cortisol levels as a novel predictor of neonatal abstinence syndrome severity: A pilot feasibility study

Neonatal abstinence syndrome (NAS) after in-utero opioid exposure remains a poorly understood condition with multiple factors contributing to severity. Exposure to maternal stress may be one contributing factor. Hair cortisol measurement represents a novel technique for assessing prenatal stress. In this pilot study, the association between maternal hair cortisol levels and NAS severity was examined in 70 postpartum women with opioid use disorder within 72 hr of delivery. Infants were monitored for NAS and treated according to institutional protocol. Forty-four (63%) of the infants were pharmacologically treated for NAS, with a mean length of hospital stay (LOS) for all infants of 14.2 (SD 9.0) days. The mean cortisol level in the mothers was 131.8 pg/mg (SD 124.7). In bivariate analysis, higher maternal hair cortisol levels were associated with shorter infant LOS (R = -.26, p = .03) and fewer infant opioid treatment days (R = -.28, p = .02). Results were no longer statistically significant in regression models after adjusting for maternal opioid and smoking. In conclusion, we demonstrated the feasibility of hair cortisol assaying within the first few days after delivery in mothers with opioid use disorder as a novel marker for NAS. The findings suggest that maternal stress may impact the severity of infant opioid withdrawal.

Novel biomarkers to assess in utero effects of maternal opioid use: First steps toward understanding short- and long-term neurodevelopmental sequelae

Maternal opioid use disorder is common, resulting in significant neonatal morbidity and cost. Currently, it is not possible to predict which opioid-exposed newborns will require pharmacotherapy for neonatal abstinence syndrome. Further, little is known regarding the effects of maternal opioid use disorder on the developing human brain. We hypothesized that novel methodologies utilizing fetal central nervous system-derived extracellular vesicles isolated from maternal blood can address these gaps in knowledge. Plasma from opioid users and controls between 9 and 21 weeks was precipitated and extracellular vesicles were isolated. Mu opioid and cannabinoid receptor levels were quantified. Label-free proteomics studies and unbiased small RNA next generation sequencing was performed in paired fetal brain tissue. Maternal opioid use disorder increased mu opioid receptor protein levels in extracellular vesicles independent of opioid equivalent dose. Moreover, cannabinoid receptor levels in extracellular vesicles were upregulated with opioid exposure indicating cross talk with endocannabinoids. Maternal opioid use disorder was associated with significant changes in extracellular vesicle protein cargo and fetal brain micro RNA expression, especially in male fetuses. Many of the altered cargo molecules and micro RNAs identified are associated with adverse clinical neurodevelopmental outcomes. Our data suggest that assays relying on extracellular vesicles isolated from maternal blood extracellular vesicles may provide information regarding fetal response to opioids in the setting of maternal opioid use disorder. Prospective clinical studies are needed to evaluate the association between extracellular vesicle biomarkers, risk of neonatal abstinence syndrome and neurodevelopmental outcomes.

Analgesia, Opioids, and Other Drug Use During Pregnancy and Neonatal Abstinence Syndrome

When opioid misuse rises in the United States, pregnant women and their neonates are affected. This article summarizes the use of Food and Drug Administration-approved products, including methadone, buprenorphine, and the combination formulation of buprenorphine and naloxone to treat adult opioid use disorder during the perinatal period. All labels include pregnancy, neonatal, and lactation information and note the accepted use of these medications during the perinatal period if the benefits outweigh the risks. A summary of the neonatal abstinence syndrome definition, its assessment tools, treatment approaches, and future genetic directions are provided.

The role of mother-infant bond in neonatal abstinence syndrome (NAS) management

The opioid crisis affects pregnant women and their infants. In the past two decades, the number of infants born with neonatal abstinence syndrome (NAS) has quadrupled causing the cost of healthcare expenditures to climb sharply. Pharmacological and non-pharmacological approaches are recommended for the management of NAS. Despite the attention NAS has recently received, treatment recommendations are limited to the hospital setting with much less focus on discharge planning. Additionally, the literature on NAS management does not consider research promoting mother-infant attachment. Recently, more emphasis has been placed on taking a holistic approach to NAS management. However, scholarly writings and research in this area are scarce. This article provides a review of current literature on NAS management and attachment-based interventions. Recommendations for practice and future research focused on holistic, non-pharmacological approaches to NAS management are provided.

The genetics and epigenetics of Neonatal Abstinence Syndrome

Neonatal abstinence syndrome (NAS) due to in-utero opioid exposure is a growing epidemic with significant variability in clinical presentation and severity. Currently, NAS severity cannot be predicted based on clinical factors alone. To date, small studies have identified genetic variants in opioid receptor and stress response genes that are associated with differences in NAS pharmacologic treatment rates and length of hospitalization. In addition, epigenetic variation in the mu opioid receptor (OPRM1) gene has been associated with differences in NAS hospitalization outcomes. Examination of maternal genetic and epigenetic profiles may assist in prediction of NAS severity. Large-scale genomic studies are needed to elucidate the genetic architecture of and epigenetic modification related to NAS in order to develop more tailored personalized treatments for NAS.

Neonatal Abstinence Syndrome

This review examines the continuum of care of opioid-exposed infants, including the assessment of the neonate, diagnosis of neonatal abstinence syndrome, management of the syndrome including nonpharmacologic and pharmacologic care, approach to breastfeeding, pediatric follow-up care, and integration of care of the mother-infant dyad.

Early life stress and environmental influences on the neurodevelopment of children with prenatal opioid exposure

Prenatal opioid exposure has reached epidemic proportions. In the last 10 years, there has been a 242% increase in the number of babies born with the drug withdrawal syndrome known as Neonatal Opioid Withdrawal Syndrome (NOWS). Developmental outcome studies of infants with prenatal opioid exposure are limited by methodological issues including small sample sizes and lack of control for confounding variables such as exposure to poverty and maternal psychopathology. Thus, there is a critical gap in the literature that limits our ability to predict short-term effects of opioid exposure. Here we review direct neurotoxic, indirect, and stress-related pathophysiologies of prenatal opioid exposure. We describe the literature on short and long-term neurodevelopmental outcomes of children with prenatal opioid exposure, highlighting sex differences and the role of early life stress. We conclude by prioritizing avenues for future research for this group of underserved women and their children at risk for neurodevelopmental delays.

Modeling prenatal opioid exposure in animals: Current findings and future directions

The past decade has seen a drastic rise in the number of infants exposed to opioids in utero. It is unclear what lasting effect this exposure may have on these children. Animal models of prenatal opioid exposure may provide insight into potential areas of vulnerability. The present review summarizes the findings across animal models of prenatal opioid exposure, including exposure to morphine, methadone, buprenorphine, and oxycodone. Details regarding the drug, doses, and duration of treatment, as well as key findings, are summarized in tables with associated references. Finally, significant gaps in the current preclinical literature and future directions are discussed.

Oxycodone self-administration during pregnancy disrupts the maternal-infant dyad and decreases midbrain OPRM1 expression during early postnatal development in rats

Opioid use and abuse has reached epidemic levels in the United States. As these drugs are frequently used by women of reproductive age, there has been a significant increase in the number of infants born to opioid dependent women. Few preclinical studies have examined voluntary opioid intake during pregnancy, and none have used intravenous self-administration. Thus, the purpose of the current set of studies was to utilize a translational model of oxycodone self-administration in rats to determine the effects of oxycodone intake during pregnancy on early postnatal outcomes. Females were trained to intravenously self-administer oxycodone several weeks prior to mating and then continuously throughout pregnancy followed by withdrawal around the time of parturition. Offspring were monitored for weight gain and separation-induced ultrasonic vocalizations (i.e. number of calls) while dams were examined for motivated maternal responding. Neural expression of the mu opioid receptor gene OPRM1 was examined in offspring on postnatal day 1 (PND1). Results indicate that females self-administer oxycodone during pregnancy at levels similar to those observed in cycling females. Postpartum, oxycodone withdrawn females demonstrate impaired maternal responding. In offspring, while no significant group effects were observed on body weight or call number, age-dependent alterations in weight gain and call number correlated with the dams cumulative oxycodone dose during pregnancy. In addition, offspring demonstrated region specific effects of oxycodone exposure on OPRM1 on PND1. Overall, these findings demonstrate that pregnant females will voluntarily self-administer oxycodone at levels similar to cycling females when using a short access model. Further, maternal oxycodone self-administration alters the maternal-offspring dyad in a manner that is dose-dependent and results in sex- and region-specific effects on OPRM1 expression.

Will Widespread Synthetic Opioid Consumption Induce Epigenetic Consequences in Future Generations?

A growing number of evidence demonstrates that ancestral exposure to xenobiotics (pollutants, drugs of abuse, etc.) can perturb the physiology and behavior of descendants. Both maternal and paternal transmission of phenotype across generations has been proved, demonstrating that parental drug history may have significant implications for subsequent generations. In the last years, the burden of novel synthetic opioid (NSO) consumption, due to increased medical prescription of pain medications and to easier accessibility of these substances on illegal market, is raising new questions first in term of public health, but also about the consequences of the parental use of these drugs on future generations. Besides being associated to the neonatal abstinence syndrome, in utero exposure to opioids has an impact on neuronal development with long-term repercussions that are potentially transmitted to subsequent generations. In addition, recent reports suggest that opioid use even before conception influences the reactivity to opioids of the progeny and the following generations, likely through epigenetic mechanisms. This review describes the current knowledge about the transgenerational effects of opioid consumption. We summarize the preclinical and clinical findings showing the implications for the subsequent generations of parental exposure to opioids earlier in life. Limitations of the existing data on NSOs and new perspectives of the research are also discussed, as well as clinical and forensic consequences.

Neuroanatomical characteristics of youths with prenatal opioid and poly-drug exposure

Neuroanatomical and cognitive differences have been documented during childhood between children with prenatal opioid- and poly-drug exposure and controls in small samples. We investigated whether these differences persisted in larger samples of youth at older ages. Quantitative MRI and cognitive data were compared between 38 youths in the risk group and 44 youths in the non-exposed group (aged 17 to 22 years) who had been followed prospectively since birth. Most drug-exposed youths (84%) moved to permanent foster or adoptive homes before one year of age. The drug-exposed group displayed smaller neuroanatomical volumes (0.70 SD difference in total brain volume, p = 0.001), smaller cortical surface areas and thinner cortices than the comparison group. The birth weight accounted for some of the intergroup differences. Neuroanatomical characteristics partially mediated group differences in cognitive function. The present study cannot differentiate between causal factors but indicates persistent neurocognitive differences associated with prenatal opioid or poly-drug exposure.

The Epidemic of Neonatal Abstinence Syndrome, Historical References of Its' Origins, Assessment, and Management

Neonatal abstinence syndrome (NAS) refers to a constellation of signs that are present in some newborn infants resulting from the abrupt cessation of passive transfer of maternal opioids used during pregnancy. The classic NAS refers to infants born to mothers who used opioids during pregnancy, but the term has broadened to include infants whose mothers have used or abused other psychoactive substances during pregnancy that contribute to the expression of the syndrome. Pregnant women who use opioids do so illicitly, and/or as medically prescribed for pain relief, and/or as medication assisted treatment for opioid dependence. The first case of NAS in infants and the subsequent treatment (or lack thereof) was reported in 1875 and was called Congenital Morphinism. By 2012, the incidence of NAS increased to more than 30 per 1,000 hospital live births, along with an increase in the number of infants being treated pharmacologically for NAS, resulting in an increase in the length of stay and healthcare expenses. We present historical references on NAS, the various factors and events that led to its increasing prevalence and today's current epidemic. We also review the current tools to assess infants with NAS and treatment options in its management.

Focusing on the Opioid System for Addiction Biomarker Discovery

Substance use disorders (SUD) and behavioral addictions are devastating conditions that impose a severe burden on all societies, and represent difficult challenges for clinicians. Therefore, biomarkers are urgently needed to help predict vulnerability, clinical course, and response to treatment. Here, we elaborate on the potential for addiction biomarker discovery of the opioid system, particularly within the emerging framework aiming to probe opioid function in peripheral tissues. Mu, delta, and kappa opioid receptors all critically regulate neurobiological and behavioral processes that define addiction, and are also targeted by major pharmacotherapies used in the management of patients with SUD. We propose that opioid biomarkers may have the potential to improve and guide diagnosis and therapeutic decisions in the addiction field.

Increased DNA Methylation of ABCB1, CYP2D6, and OPRM1 Genes in Newborn Infants of Methadone-Maintained Opioid-Dependent Mothers

OBJECTIVE

To investigate whether in utero opioid exposure, which has been linked to adverse neurodevelopmental and social outcomes, is associated with altered DNA methylation of opioid-related genes at birth.

STUDY DESIGN

Observational cohort study of 21 healthy methadone-maintained opioid-dependent mother-infant dyads consecutively delivered at >36 weeks of gestation, and 2 comparator groups: smoking, "deprived" opioid-naïve mother-infant dyads (n = 17) and nonsmoking, "affluent" opioid-naïve mother-infant dyads (n = 15). DNA methylation of ABCB1, CYP2D6, and OPRM1 genes for mothers and babies was determined from buccal swabs. Plasma methadone concentrations were additionally measured for methadone-maintained opioid-dependent mothers.

RESULTS

DNA methylation for ABCB1 and CYP2D6 was similar in opioid-naïve infants compared with their mothers, but was less for OPRM1 (3 ± 1.6% vs 8 ± 1%, P < .0005). Opioid-exposed newborns had similar DNA methylation to their mothers for all genes studied and greater methylation of ABCB1 (18 ± 4.8% vs 3 ± 0.5%), CYP2D6 (92 ± 1.2% vs 89 ± 2.4%), and OPRM1 (8 ± 0.3% vs 3 ± 1.6%) compared with opioid-naïve newborns (P < .0005 for all 3 genes). Infant DNA methylation was not related to birth weight, length of hospital stay, maternal smoking, dose or plasma concentration of methadone at delivery, or postcode of residence.

CONCLUSIONS

In utero exposure to opioids is associated with increased methylation of opioid-related genes in the newborn infant. It is not clear whether these findings are due to opioid exposure per se or other associated lifestyle factors.