Prenatal Exposure to Primary Aromatic Amines: Structure-Dependent Transplacental Transfer Mechanism and Toxicity

Primary aromatic amines (PAAs) are carcinogenic chemicals that are ubiquitous in indoor environments. However, little is known about their placental transfer and associated toxicity. Herein, we developed an approach integrating human biomonitoring, uterine perfusion experiments in pregnant rats, computational modeling, and <i>in vitro</i> placental cell bioassays. Nine of 30 PAAs including 8 PAAs with a monobenzene ring (e.g., aniline, ANI; <i>ortho</i>-toluidine, <i>o</i>-TD; <i>para</i>-toluidine, <i>p</i>-TD; <i>ortho</i>-anisidine, <i>o</i>-ANSD; 4-ethylaniline, 4-EA; 4-chloroaniline, 4-CA; and 3-chloroaniline, 3-CA) and 1 PAA with bis-benzene ring (2-naphthylamine, 2-NA), were widely detected (detection rate >50%) in 47 paired maternal and cord serum samples with median Σ₉PAAs concentrations of 11.2 and 11.7 ng/mL, respectively. Transplacental transfer efficiencies (TTEs) of PAAs were notably high, with median values ranging from 0.91 (<i>p</i>-CD) to 1.60 (2-NA), indicating efficient placental transfer. Excluding 2-NA, both biomonitoring data and rat uterine perfusion experiments revealed a significant negative correlation between log <i>K</i>_ow and TTEs (or PAA concentrations in fetal rat), supporting passive diffusion as a mechanism involved in placental transfer of monoaromatic PAAs. Crucially, molecular docking and molecular dynamics simulations indicated that 2-NA forms dynamically stable complexes with specific solute carrier (SLC) and ATP-binding cassette (ABC) transporters, suggesting a transporter-mediated active transport process. Cytotoxicity assays further indicated that 2-NA exhibited the highest toxicity among all PAAs. Moreover, in syncytialized BeWo cells, 2-NA exposure significantly compromised placental barrier integrity and function. The widespread presence of PAAs in maternal and fetal serum underscores the need for regulatory measures to reduce exposure, particularly among pregnant women and fetuses.