Placental distribution of endogenous and exogenous substances: A pilot study utilizing cryo-sampled specimen off delivery room

Introduction: Reliability in the use of placentome (including placenta, umbilical cord, and cord blood) biomarkers requires an understanding of their distributions. Here we aim to develop a simple and proper placenta sampling scheme, and to evaluate the placental distributions of biomarkers. Methods: We developed a continuous cooling chain protocol off delivery room and cryo-subsampling method for placenta sampling. The levels of thyroid hormones (THs), elements, persistent organic pollutants (POPs), monoamines, and vitamin E were measured using UPLC-Q-TOF-MS, HPLC-ICP-MS, HPLC-EcD, and HRGC-HRMS, respectively. The distributions of biomarkers were assessed. Results: In human placentome, _L-thyroxine (T₄), Cd, Se, Zn, Cu, Fe, Ca, K, Mg, α-tocopherol, β-tocopherol, and β-tocotrienol levels were higher in placenta than in umbilical cord, while Pb and Mn were concentrated in human cord. In porcine placentome, T₄, 3,3′,5′-triiodo-_L-thyronine (rT₃), 3,3′-diiodo-_L-thyronine, Cd, Pb, Zn, K, and Al levels were higher in the cord. The intraclass correlation coefficient (ICC) was <0.4 for 3,3′,5-triiodo-_L-thyronine, rT₃, α-tocopherol, and 7 elements in human basal plate, indicating low reliability. rT₃, Cd, Zn, Mn, and Cu were significantly concentrated in the central region in human placenta, while higher levels of As, Cd, Cr, and Al were found in the periphery region in porcine placenta. Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) showed moderate reliability (ICC: 0.40–0.98) except PCB-81, -126, and BDE-208, while polychlorinated dibenzo-p-doixins/furans (PCDD/Fs) showed poor reliability (ICC: 0.07–0.31). Discussion: These results highlight the complexity of placenta sampling. This study provides a novel and simple sampling approach in investigating placental exposomics.