Title: Prenatal acetaminophen exposure as a risk factor for Attention Deficit Hyperactivity Disorder (ADHD)
Description: Despite evidence of an association between prenatal acetaminophen exposure and attention deficit hyperactivity disorder (ADHD) in offspring, the causal role of prenatal acetaminophen exposure in child ADHD remains unclear owing to limitations of prior studies. Prior studies have relied on maternal self-report, failed to quantify acetaminophen dose, and lacked mechanistic insight. Chapter 1 formally introduces this topic and provides background information summarizing the high prevalence of ADHD, widespread use of acetaminophen during pregnancy, and potential molecular mechanisms through which the drug may harm fetal development. In Chapter 2, we examined the association between prenatal acetaminophen exposure measured in meconium and ADHD in children aged 6 to 7 years, along with the potential for mediation by functional brain connectivity. Data came from a prospective birth cohort study from the Centre Hospitalier Université de Sherbrooke in Sherbrooke, Québec, Canada. We included 393 eligible children, of whom 345 had meconium samples collected at delivery and information on ADHD diagnosis.

Mothers were enrolled from September 25, 2007, to September 10, 2009, at their first prenatal care visit or delivery. Acetaminophen levels were measured in meconium, and physician diagnosis of ADHD was determined at follow-up when children were aged 6 to 7 years or from medical records. Additionally, when children were aged 9 to 11 years, resting-state brain connectivity was assessed with magnetic resonance imaging, and attention problems and hyperactivity were assessed with the Behavioral Assessment System for Children Parent Report Scale. Associations between meconium acetaminophen levels and outcomes were estimated with linear and logistic regressions weighted on the inverse probability of treatment to account for potential confounders. Causal mediation analysis was used to test for mediation of the association between prenatal acetaminophen exposure and hyperactivity by resting-state brain connectivity. Among the 345 children included in the analysis (177 boys [51.3%]; mean [SD] age, 6.58 [0.54] years), acetaminophen was detected in 199 meconium samples (57.7%), and ADHD was diagnosed in 33 children (9.6%).

Compared with no acetaminophen, detection of acetaminophen in meconium was associated with increased odds of ADHD (odds ratio [OR], 2.43; 95%CI, 1.41-4.21). A dose-response association was detected; each doubling of exposure increased the odds of ADHD by 10% (OR, 1.10; 95%CI, 1.02-1.19). Children with acetaminophen detected in meconium showed increased negative connectivity between frontoparietal and default mode network nodes to clusters in the sensorimotor cortices, which mediated an indirect effect on increased child hyperactivity (14%; 95%CI, 1%-26%). In Chapter 3, we used data from the same Canadian birth cohort to examine whether prenatal acetaminophen exposure is associated with adverse birth outcomes and/or pregnancy complications, and if birth outcomes may mediate the association of prenatal acetaminophen with child ADHD. This study included 393 children for whom acetaminophen was measured in meconium at delivery. We tested associations of prenatal acetaminophen with birthweight, preterm birth, gestational age, small and large for gestational age, gestational diabetes, preeclampsia, and high blood pressure.

Using causal mediation analyses, we assessed whether birth outcomes mediated the association of prenatal acetaminophen with ADHD. We imputed missing data via multiple imputation and used inverse probability weighting to account for confounding and selection bias. Prenatal acetaminophen exposure was associated with decreased birthweight by 136 g (β = −136; 95% CI [−229, −43]), 20% increased weekly hazard of delivery (hazard ratio = 1.20; 95% CI [1.00, 1.43]), and over 60% decreased odds of being born large for gestational age (odds ratio = 0.38; 95% CI [0.20, 0.75]). Prenatal acetaminophen was not associated with small for gestational age, preterm birth, or any pregnancy complications. Causal mediation effects were non-significant for all birth outcomes in both unadjusted and adjusted models, indicating no evidence that birth outcomes linked prenatal acetaminophen exposure with child ADHD. In Chapter 4, we examined the effects of developmental acetaminophen exposure on mouse behavior and frontal cortex gene expression.

Although prior studies have investigated neurodevelopmental effects of prenatal acetaminophen exposure in rodents, the results of these studies are not always in agreement. Additionally, no mouse studies of prenatal acetaminophen exposure have investigated offspring attention deficits in behavior tasks specifically designed to measure attention, and no prior rodent studies have utilized ‘omics’ technologies for an untargeted exploration of potential mechanisms. We randomly assigned pregnant mice (starting embryonic day 4-10) to receive acetaminophen (150 mg/kg/day) or vehicle control through postnatal day 14. We employed a battery of behavior tests for 111 mouse offspring, including pup ultrasonic vocalizations, elevated plus maze, open field test, CatWalk, pre-pulse inhibition, and 5-choice serial reaction time task. Frontal cortex was collected at birth from 24 pups for RNA-sequencing. Developmental acetaminophen treatment resulted in increased pup vocalizations after separation from the litter, as well as decreased ambulation and vertical rearings in the open field task among male but not female offspring.

Acetaminophen treatment was also associated with altered frontal cortex gene expression relating to glutathione and cytochrome p450 metabolism, DNA damage, and the endocrine and immune systems. Together with the multitude of other cohort studies showing adverse neurodevelopment associated with prenatal acetaminophen exposure, this work suggests caution should be used in administering acetaminophen during pregnancy. In humans, we found that prenatal acetaminophen exposure was associated with child ADHD, altered resting-state brain connectivity, and adverse birth outcomes. Furthermore, our results suggest altered brain connectivity as a potential underlying mechanism linking prenatal acetaminophen use with child hyperactivity. While adverse birth outcomes such as preterm birth and reduced birthweight are known to be associated with ADHD, we found no evidence for mediation by birth outcomes of the association between prenatal acetaminophen exposure and ADHD. In mice, we found that developmental acetaminophen treatment resulted in elevated anxiety-like behaviors in male offspring, as well as gene expression changes in the frontal cortex.

Future studies are needed to explore whether the altered molecular pathways revealed by RNA-sequencing directly link acetaminophen exposure with offspring behavior changes.