Association of Prenatal Exposure to Ambient Air Pollution With Circulating Histone Levels in Maternal Cord Blood

IMPORTANCE: Exposure to ambient air pollution has been associated with the risk of carcinogenesis in later life. Changes in histone modifications might have long-term adverse health effects. OBJECTIVE: To investigate the association of prenatal exposure to ambient air pollution with levels of circulating total histone H3 and specific trimethylation marks (ie, H3 lysine 4, H3 lysine 36) in maternal cord blood. DESIGN, SETTING, AND PARTICIPANTS: The Environmental Influence on Aging (ENVIRONAGE) birth cohort study included 609 mothers and their newborns. Participants were recruited when mothers entered the Hospital East Limburg (Genk, Belgium) for delivery between February 2010 and January 2017. The inclusion criteria were singleton pregnancies and the ability to fill out questionnaires in Dutch. Data analysis was conducted from March to August 2019. EXPOSURES: Exposure to particulate matter with a diameter less than 2.5 μm (PM(2.5)), black carbon, and nitrogen dioxide during pregnancy was modeled with a high-resolution air pollution model on the basis of maternal address for each trimester of pregnancy as well as for the entire pregnancy. MAIN OUTCOMES AND MEASURES: Circulating total histone H3 levels and specific trimethylation marks (ie, trimethylated H3 lysine 4 and trimethylated H3 lysine 36) in cord blood. RESULTS: A total of 609 mother-newborn pairs were included in the study. Mean (SD) maternal age was 29.3 (4.6) years, 391 mothers (64.2%) never smoked, and 314 (51.3%) had a high education level. Overall, 322 newborns (52.4%) were boys, and mean (SD) birth weight was 3414 (485) g. Participants experienced mean (SD) exposure to PM(2.5), black carbon, and nitrogen dioxide of 13.4 (2.6) μg/m(3), 1.29 (0.31) μg/m(3), and 17.98 (4.57) μg/m(3), respectively, during their entire pregnancies. Trimethylated H3 lysine 4 and total histone H3 were positively associated with gestational PM(2.5) exposure, with a 74.4% increment (95% CI, 26.7% to 140.2%, P < .001) and a 40.2% increment (95% CI, 24.1% to 58.3%, P < .001), respectively, observed for each 5-μg/m(3) increase in PM(2.5) exposure during the entire pregnancy. For the same exposure window, trimethylated H3 lysine 36 levels were inversely associated with PM(2.5) exposure (−34.4%; 95% CI, −50.1% to −13.7%; P = .003). Exposure to black carbon during the entire pregnancy was positively associated with trimethylated H3 lysine 4 (38.4%; 95% CI, 6.2% to 80.3%; P = .003). CONCLUSIONS AND RELEVANCE: Associations of ambient air pollution with cord plasma histone H3 modifications during early life might indicate that circulating histones are a risk factor in the development of air pollution–associated disease later in life. Additional study is required to correctly estimate the long-term consequences of our findings.