Determinants of placental iodine concentrations in a mild-to-moderate iodine-deficient population: an ENVIRONAGE cohort study

Study of iodine transport and thyroid hormone levels in the human placenta under different iodine nutritional status

Iodine and thyroid hormones (TH) transport in the placenta are essential for fetal growth and development, but there is little research focus on the human placenta. The research aimed to investigate iodine and TH transport mechanisms in the human placenta. The placenta was collected from sixty healthy pregnant women. Urinary iodine concentration (UIC), serum iodine concentration (SIC), placenta iodine storage (PIS) and the concentration of serum and placenta TH were examined. Five pregnant women were selected as insufficient intake (II), adequate intake (AI) and above requirements intake (ARI) groups. Localisation/expression of placental sodium/iodide symporter (NIS) and Pendrin were also studied. Results showed that PIS positively correlated with the UIC (R = 0·58, P < 0·001) and SIC (R = 0·55, P < 0·001), and PIS was higher in the ARI group than that in the AI group (P = 0·017). NIS in the ARI group was higher than that in the AI group on the maternal side of the placenta (P < 0·05). NIS in the II group was higher than that in the AI group on the fetal side (P < 0·05). In the II group, NIS on the fetal side was higher than on the maternal side (P < 0·05). Pendrin was higher in the II group than in the AI group on the maternal side (P < 0·05). Free triiodothyronine (r = 0·44, P = 0·0067) and thyroid-stimulating hormone (r = 0·75, P < 0·001) between maternal and fetal side is positively correlated. This study suggests that maternal iodine intake changes the expression of NIS and Pendrin, thereby affecting PIS. Serum TH levels were not correlated with placental TH levels.

Mechanism of multi-organ compensation under different iodine intake in pregnant rats: results from a repeated-measures study of iodine metabolism

PURPOSE

This study aimed to explore the differences in iodine metabolism and expression of NIS and Pendrin in pregnant rats under different iodine nutritional status.

METHODS

Female Wistar rats were divided into four groups: low iodine (LI), normal iodine (NI), ten fold high iodine (10HI), and fifty fold high iodine (50HI). The intervention began after one week of adaptive feeding. Iodine metabolism experiments were performed beginning on the 15th day of pregnancy. 24-h iodine intake and excretion were calculated. The concentrations of iodine in urine, fecal, thyroid, and placenta were measured by ICP-MS. PCR and Western Blot were used to detect the mRNA levels and cell membrane protein of sodium/iodide symporter (NIS) and Pendrin in the small intestine, thyroid, kidney, and placenta.

RESULTS

Fecal iodine excretion (FIE) and urinary iodine excretion (UIE) in the 50HI group were significantly higher than those in the NI group (P < 0.05). The NIS protein and mRNA in the kidney and small intestine have an upward trend in iodine deficiency and a downward trend in iodine excess. Thyroid and placental iodine storage in the 50HI group were significantly higher than those in the NI group (P < 0.05). NIS, Pendrin protein, and mRNA in the thyroid and placenta tend to increase when iodine is deficient and decrease when there is excess.

CONCLUSION

Iodine excretion and iodine stores in the placenta and thyroid gland are positively correlated with iodine intake. NIS and Pendrin are also regulated by iodine intake.

Prenatal alcohol exposure is associated with changes in placental gene co-expression networks

Alcohol consumption during pregnancy can result in a range of adverse postnatal outcomes among exposed children. However, identifying at-risk children is challenging given the difficulty to confirm prenatal alcohol exposure and the lack of early diagnostic tools. Placental surveys present an important opportunity to uncover early biomarkers to identify those at risk. Here, we report the first transcriptome-wide evaluation to comprehensively evaluate human placental pathways altered by fetal alcohol exposure. In a prospective longitudinal birth cohort in Cape Town, South Africa, we performed bulk tissue RNAseq in placenta samples from 32 women reporting heavy drinking during pregnancy and 30 abstainers/light drinkers. Weighted gene co-expression network analysis (WGCNA) and differential gene expression analysis were performed to assess associations between fetal alcohol exposure and placental gene expression patterns at a network-wide and single gene level, respectively. The results revealed altered expression in genes related to erythropoiesis and angiogenesis, which are implicated in established postnatal phenotypes related to alcohol exposure, including disruptions in iron homeostasis, growth, and neurodevelopment. The reported findings provide insights into the molecular pathways affected by prenatal alcohol exposure and highlight the potential of placental biomarkers for detecting and understanding the effects of alcohol on fetal development.

Associations of Maternal Serum Iodine Concentration with Obstetric Complications and Birth Outcomes-Longitudinal Analysis Based on the Huizhou Mother-Infant Cohort, South China

This study aimed to explore the temporal associations between maternal serum iodine concentration (SIC) and common pregnancy outcomes in Chinese women. Eligible singleton pregnant women aged 20-34 years were selected, and their fasting blood samples were collected during early (T1, n = 1101) and mid-pregnancy (T2, n = 403) for SIC testing by inductively coupled plasma mass spectrometry. Multivariable linear regression indicated that log₁₀SIC at T1 (β = -0.082), T2 (β = -0.198), and their % change (β = -0.131) were inversely associated with gestational weight gain (GWG, all p < 0.05). Maternal log₁₀SIC at both T1 (β = 0.077) and T2 (β = 0.105) were positively associated with the Apgar score at 1 min (both p < 0.05). Women in the third quartile (Q3) of SIC at T1 had a lower risk of small for gestational age (SGA, OR = 0.405, 95% CI: 0.198-0.829) compared with those in Q4. Restricted cubic spline regression suggested a U-shaped association between SIC and SGA risk, and SIC above 94 μg/L at T1 was the starting point for an increased risk of SGA. The risk of premature rupture of membrane (PROM) increased by 96% (OR = 1.960, 95% CI: 1.010-3.804) in Q4 compared to that in Q1. Our longitudinal data from an iodine-replete region of China indicated that high maternal SIC could restrict GWG and improve Apgar scores at delivery, but might increase the risk of SGA and PROM.

Iodine Deficiency, Maternal Hypothyroxinemia and Endocrine Disrupters Affecting Fetal Brain Development: A Scoping Review

This scoping review critically discusses the publications of the last 30 years on the impact of mild to moderate iodine deficiency and the additional impact of endocrine disrupters during pregnancy on embryonal/fetal brain development. An asymptomatic mild to moderate iodine deficiency and/or isolated maternal hypothyroxinemia might affect the development of the embryonal/fetal brain. There is sufficient evidence underlining the importance of an adequate iodine supply for all women of childbearing age in order to prevent negative mental and social consequences for their children. An additional threat to the thyroid hormone system is the ubiquitous exposure to endocrine disrupters, which might exacerbate the effects of iodine deficiency in pregnant women on the neurocognitive development of their offspring. Ensuring adequate iodine intake is therefore essential not only for healthy fetal and neonatal development in general, but it might also extenuate the effects of endocrine disruptors. Individual iodine supplementation of women of childbearing age living in areas with mild to moderate iodine deficiency is mandatory as long as worldwide universal salt iodization does not guarantee an adequate iodine supply. There is an urgent need for detailed strategies to identify and reduce exposure to endocrine disrupters according to the "precautional principle".

Adverse Effects of Black Carbon (BC) Exposure during Pregnancy on Maternal and Fetal Health: A Contemporary Review

Black carbon (BC) is a major component of ambient particulate matter (PM), one of the six Environmental Protection Agency (EPA) Criteria air pollutants. The majority of research on the adverse effects of BC exposure so far has been focused on respiratory and cardiovascular systems in children. Few studies have also explored whether prenatal BC exposure affects the fetus, the placenta and/or the course of pregnancy itself. Thus, this contemporary review seeks to elucidate state-of-the-art research on this understudied topic. Epidemiological studies have shown a correlation between BC and a variety of adverse effects on fetal health, including low birth weight for gestational age and increased risk of preterm birth, as well as cardiometabolic and respiratory system complications following maternal exposure during pregnancy. There is epidemiological evidence suggesting that BC exposure increases the risk of gestational diabetes mellitus, as well as other maternal health issues, such as pregnancy loss, all of which need to be more thoroughly investigated. Adverse placental effects from BC exposure include inflammatory responses, interference with placental iodine uptake, and expression of DNA repair and tumor suppressor genes. Taking into account the differences in BC exposure around the world, as well as interracial disparities and the need to better understand the underlying mechanisms of the health effects associated with prenatal exposure, toxicological research examining the effects of early life exposure to BC is needed.

Effects of maternal iodine nutritional status on neurodevelopmental and cognitive function of rat offspring

Objectives

This study aimed to explore the effect of maternal iodine status on the brain development of offspring in rats. Since in human studies, the interference of environmental factors and other nutrients cannot be removed.

Materials and methods

A total of 48 female Wistar rats were randomly divided into four groups: low iodine (LI), normal iodine (NI), 10-fold high iodine (10HI), and 50-fold high iodine (50HI). The rats were killed on the 15th day of pregnancy and lactation after collecting 24-h urine. The iodine concentration in 24-h urine, blood, and placenta of pregnant rats, and 24-h urine, milk, blood, and mammary glands of lactating rats was determined by inductively coupled plasma mass spectrometry. The thyroid hormone of pregnant and lactating rats was detected by chemiluminescence. The offspring were subjected to the Morris water maze on the 10th day after birth. Serum was collected to detect the thyroid hormone of offspring. The protein expression of neuroendocrine-specific protein (NSP)-A and brain-derived neurotrophic factor (BDNF) in the offspring brain were studied.

Results

Iodine storage in the placenta during pregnancy and mammary glands during lactation was positively correlated with iodine intake, and iodine storage in the placenta and mammary glands in the 50HI group was significantly higher than that in the NI group (P = 0.045 and P = 0.040). Compared with the NI group, the offspring thyroid-stimulating hormone (TSH) level was significantly higher in the 10HI group (P = 0.046), and the FT4 level was significantly lower in the 50HI group (P = 0.032). The Morris water maze showed that LI and 50HI groups required longer time and distance to find the platform than the NI group (P &lt; 0.001). The platform crossing numbers in the LI and 50HI groups decreased significantly (P &lt; 0.001). The expression of NSP-A in offspring brain was lower in the 10HI and 50HI groups than in the NI group (P = 0.026 and P = 0,008). BDNF expression levels were significantly lower in the LI, 10HI, and 50HI groups than in the NI group (P &lt; 0.001).

Conclusion

Maternal iodine intake affects iodine storage in the placenta and lactating mammary gland, which in turn affects thyroid function and BDNF and NSP-A expression in the offspring.

Prenatal alcohol consumption and placental outcomes: a systematic review and meta-analysis of clinical studies

OBJECTIVE

A systematic review was conducted to determine placental outcomes following prenatal alcohol exposure in women.

DATA SOURCES

The search terms "maternal OR prenatal OR pregnant OR periconception" AND "placenta" AND "alcohol OR ethanol" were used across 5 databases (PubMed, Embase, Cochrane Library, Web of Science, and CINAHL) from inception until November 2020.

STUDY ELIGIBILITY CRITERIA

Articles were included if they reported placental outcomes in an alcohol exposure group compared with a control group. Studies were excluded if placentas were from elective termination before 20 weeks' gestation, animal studies, in vitro studies, case studies, or coexposure studies.

METHODS

Study quality was assessed by 2 reviewers using the Newcastle-Ottawa Quality Assessment Scale. Title and abstract screening was conducted by 2 reviewers to remove duplicates and irrelevant studies. Remaining full text articles were screened by 2 reviewers against inclusion and exclusion criteria. Placental outcome data were extracted and tabulated separately for studies of placentation, placental weight, placental morphology, and placental molecular studies. Meta-analyses were conducted for outcomes reported by >3 studies.

RESULTS

Database searching retrieved 640 unique records. Screening against inclusion and exclusion criteria resulted in 33 included studies. The quality assessment identified that 61% of studies were high quality, 30% were average quality, and 9% were low quality. Meta-analyses indicated that prenatal alcohol exposure increased the likelihood of placental abruption (odds ratio, 1.48; 95% confidence interval, 1.37-1.60) but not placenta previa (odds ratio, 1.14; 95% confidence interval, 0.84-1.34) and resulted in a reduction in placental weight of 51 g (95% confidence interval, -82.8 to -19.3). Reports of altered placental vasculature, placental DNA methylation, and gene expression following prenatal alcohol exposure were identified. A single study examined placentas from male and female infants separately and found sex-specific placental outcomes.

CONCLUSION

Prenatal alcohol exposure increases the likelihood of placental abruption and is associated with decreased placental weight, altered placental vasculature, DNA methylation, and molecular pathways. Given the critical role of the placenta in determining pregnancy outcomes, further studies investigating the molecular mechanisms underlying alcohol-induced placental dysfunction are required. Sex-specific placental adaptations to adverse conditions in utero have been well documented; thus, future studies should examine prenatal alcohol exposure-associated placental outcomes separately by sex.

Lower iodine storage in the placenta is associated with gestational diabetes mellitus

BACKGROUND

The micronutrient iodine is essential for a healthy intrauterine environment and is required for optimal fetal growth and neurodevelopment. Evidence linking urinary iodine concentrations, which mainly reflects short-term iodine intake, to gestational diabetes mellitus (GDM) is inconclusive. Although the placental concentrations would better reflect the long-term gestational iodine status, no studies to date have investigated the association between the placental iodine load and the risk at GDM. Moreover, evidence is lacking whether placental iodine could play a role in biomarkers of insulin resistance and β-cell activity.

METHODS

We assessed the incidence of GDM between weeks 24 and 28 of gestation for 471 mother-neonate pairs from the ENVIRONAGE birth cohort. In placentas, we determined the iodine concentrations. In maternal and cord blood, we measured the insulin concentrations, the Homeostasis Model Assessment (HOMA) for insulin resistance (IR) index, and β-cell activity. Logistic regression was used to estimate the odds ratios (OR) of GDM, and the population attributable factor (PAF) was calculated. Generalized linear models estimated the changes in insulin, HOMA-IR, and β-cell activity for a 5 μg/kg increase in placental iodine.

RESULTS

Higher placental iodine concentrations decreased the risk at GDM (OR = 0.82; 95%CI 0.72 to 0.93; p = 0.003). According to the PAF, 54.2% (95%CI 11.4 to 82.3%; p = 0.0006) of the GDM cases could be prevented if the mothers of the lowest tertile of placental iodine would have placental iodine levels as those belonging to the highest tertile. In cord blood, the plasma insulin concentration was inversely associated with the placental iodine load (β = - 4.8%; 95%CI - 8.9 to - 0.6%; p = 0.026).

CONCLUSIONS

Higher concentrations of placental iodine are linked with a lower incidence of GDM. Moreover, a lower placental iodine load is associated with an altered plasma insulin concentration, HOMA-IR index, and β-cell activity. These findings postulate that a mild-to-moderate iodine deficiency could be linked with subclinical and early-onset alterations in the normal insulin homeostasis in healthy pregnant women. Nevertheless, the functional link between gestational iodine status and GDM warrants further research.

Ambient air pollution exposure during the late gestational period is linked with lower placental iodine load in a Belgian birth cohort

BACKGROUND

Adequate intake of iodine is required for the production of thyroid hormones and contributes in pregnant women to a healthy brain development and growth in their offspring. To date, some evidence exists that fine particulate air pollution is linked with the fetal thyroid hormone homeostasis. However, possible effects of air pollutants on the placental iodine storage have not been investigated so far.

OBJECTIVES

We investigated the association between air pollution exposure to particulate matter with a diameter less than 2.5 µm (PM_2.5), NO₂, and black carbon and the placental iodine load.

METHODS

The current study is part of the ENVIRONAGE birth cohort and included 470 mother-newborn pairs. Iodine concentrations were measured in placental tissue. A high-resolution air pollution model was used to estimate the daily exposure to PM_2.5, NO₂, and black carbon over the entire pregnancy based on the maternal residential addresses. Distributed lag nonlinear models (DLNMs) were used to estimate gestational week-specific associations between placental iodine concentrations and the air pollutants to understand the impact of specific exposure windows.

RESULTS

PM_2.5 showed a positive association with placental iodine concentration between the 16^th and 22^nd week of gestation. In contrast, a significant inverse association between PM_2.5 and placental iodine concentration was observed in gestational weeks 29-35. The effect estimate, for a 5 µg/m³ increment in PM_2.5 concentration, was the strongest at week 32 (β -0.11 µg/kg; 95%CI: -0.18 to -0.03). No associations were observed between placental iodine concentrations and NO₂ or black carbon. Assuming causality, we estimated that placental iodine mediated 26% (-0.33 pmol/L; 95%CI: -0.70 to 0.04 pmol/L) of the estimated effect of a 5 µg/m³ increment in PM_2.5 exposure on cord blood free thyroxine (FT₄) concentrations.

CONCLUSION

In utero exposure to particulate matter during the third trimester of pregnancy is linked with a lower placental iodine load. Furthermore, the effect of air pollution on cord blood FT₄ levels was partially mediated by the placental iodine load.