In utero exposure to persistent organic pollutants (POPs) can result in thyroid function disorder, leading to concerns about their impact on fetal and neonatal development. The present study was performed to investigate the associations between placental levels of various POPs and thyroid hormones (THs). In a prospective Danish study initially established for assessing congenital cryptorchidism, 58 placenta samples were collected from mothers of boys born with (28) and without (30) cryptorchidism. The concentrations of polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs), organotin chemicals (OTCs), organochlorine pesticides (OCPs), thyroxine (T₄), 3,3’,5-triiodothyronine (T₃), and 3,3’,5’-triiodothyronine (rT₃) were measured. The associations between placental THs and various POPs were analyzed using multiple linear regression. Five PBDEs, 35 PCBs, 14 PCDD/Fs, 3 OTCs, 25 OCPs, T₄, T₃, and rT₃ were measured. No correlation between THs and the odds of cryptorchidism was found. Several POPs were significantly associated with THs: a) T₄ was inversely associated with BDEs 99, 100, ΣPBDE, and 2378-TeCDD, and positively associated with 1234678-HpCDF; b) T₃ was positively associated with 2378-TeCDF and 12378-PeCDF; c) rT₃ was positively associated with PCB 81, 12378-PeCDF and 234678-HxCDF, and inversely associated with tributyltin (TBT), ΣOTC, and methoxychlor (MOC). These results revealed that POP exposures were associated with TH levels in placenta, a possible mechanism for the impacts of POP exposures on children’s growth and development. This study provides new insight into the complexity of thyroid-disrupting properties of POPs. More research is needed to elucidate the biological consequences of POP exposures.

The placenta is a highly specialized organ, which ensures nutrient uptake, waste elimination, provides thermo-regulation, prevents passage of some xenobiotic molecules and regulates the quantity of thyroid hormones (TH) necessary for the fetal development. It is known, that even minor changes in maternal TH levels, can alter the fetal growth. Several factors can modify TH levels during pregnancy. Among them, increasing evidences show that prenatal exposure to persistent organic pollutants (POP), such as brominated flame-retardants (PBDE), polychlorinated dibenzo-p-dioxins and furans (PCDD/F), and polychlorinated biphenyls (PCB), could disrupt the maternal TH regulation system. Some years ago, we investigated the association between some POP measured in placenta and congenital cryptorchidism [1–3]. Congenital cryptorchidism is a genital malformation that occurs in 2-9% of newborns and it is associated with decreased semen quality and higher risk of testis cancer. Several factors seem implicated in such pathology; however, the possible relationship between cryptorchidism and thyroid hormone levels during the uterine life in boys born with such malformation has been poorly investigated. The aim of this study was to analyze the level of thyroxine (T4), 3,3′,5-triiodo-L-thyronine (T3), 3,3′,5′-triiodo-L-thyronine (rT3) in 58 placenta samples (28 cryptorchid boys, 30 controls) using a LC-MS method recently developed in our group [4]. The samples were randomly selected at the end of the 3rd trimester and collected at birth. The entire placenta was homogenized prior analysis and stored at −20° C. Results: No difference was detected in thyroid hormone values between the case and control group. No differences between the two groups with respect to maternal smoking, maternal age, BMI, and birth weight was found. Only a difference was seen in gestational age between case and control. Although no association of placental thyroid hormone levels with congenital cryptorchidism was found, for more complete overview, future study should include TH measurement in maternal and fetal placenta as well as in the cord blood. Reference: Shen, H, et al. Placenta, 26, (2005), 512-514 Shen, H. et al. Human Reproduction, 23, (2008), 201-210 Shen, H. et al. Chemosphere, 67, (2007), S256-S262 De Angelis, M. et al. Journal of Chromatography B, 1033-1034, (2016), 413-420

Thyroid hormones (TH) of maternal origin are critical for the proper fetal development, especially during early pregnancy. Even minor changes in maternal TH circulation can lead to various adverse outcomes. Recent studies found that the metabolites of thyroxine (T₄) also play an important physiological role. For example, 3,5-diiodo-L-thyronine (T₂) and 3,3′-diiodo-L-thyronine (rT₂) can suppress the thyroid stimulating hormone (TSH) level and increase the resting metabolic rate. 3-iodothyronamine (T₁AM) administration in mice leads to a hypometabolic state. These metabolites may have influences on the fetus. Having the capacity to make a comprehensive analysis of T₄ and the metabolites in placenta provides a diagnostic tool for the placental TH homeostasis. Routine TH assessment has long been achieved by measuring T₄, triiodo-L-thyronine (T₃), and TSH in blood using immunoassay (IA) method, which is of high sensitivity, but is prone to nonspecific interferences. Methods based on liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (LC-MS/MS) showed better accuracy and reliability. In this study, we report a method for the determination of T₄, T₃, 3,3′,5′-triiodo-L-thyronine (rT₃), T₂, rT₂, 3-iodo-L-thyronine (T₁), and T₁AM in the placenta. The method was optimized using isotope (¹³C-T₄, ¹³C-T₃, ¹³C-rT₃, ¹³C-T₂) dilution methodology and determined by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS). The calibration ranges from 0.5 to 150 ng/ml with R² values > 0.99. The method detection limits (MDLs) and the method quantification limits (MQLs) were 0.01–0.2 ng/g and 0.04–0.7 ng/g, respectively. The spike-recoveries for THs (except for T₁ and T₁AM) were between 81.0% and 112%, with a coefficient of variation (CV) of 0.5–6.2%. The intra-day CVs and inter-day CVs were 0.5% – 10.3% and 1.19% – 8.88%, respectively. The method was adopted for TH measurement in human and mouse placenta. The concentrations of T₄, T₃, rT₃, and T₂ were 22.9–35.0 ng/g, 0.32–0.46 ng/g, 2.86–3.69 ng/g, and 0.16–0.26 ng/g in human placenta, and 2.05–3.51 ng/g, 0.37–0.62 ng/g, 0.96–1.3 ng/g, and 0.07–0.13 ng/g in mouse placenta, respectively. The presence of T₂ was tracked in placenta tissue for the first time, indicating improved selectivity and sensitivity of our method. The validated method allows comprehensive evaluation of total T₄ and metabolites in the placenta.