Suppression of progesterone synthesis in human trophoblast cells by fine particulate matter primarily derived from industry

The relationship between cooking fuel use and sex hormone levels: A cross-sectional study and Mendelian randomization study

PURPOSE

The aim of this study was to investigate the effect of solid fuel use on serum sex hormone levels. Furthermore, the effects of improved kitchen ventilation and duration of cooking time on the relationship between solid fuel use and serum sex hormone levels will be further explored.

METHODS

In this cross-sectional study, 5386 individuals were recruited. Gender and menopausal status modified associations between solid fuel type and serum sex hormone levels was investigated through generalized linear models and further analyzed by improving kitchen ventilation and length of cooking time on the relationship between solid fuel use and serum sex hormone levels. To identify the causal association, mendelian randomization of two-sample was performed.

RESULTS

In observational analyses, for ln-17-hydroxyprogesterone, ln-testosterone, and ln-androstenedione among premenopausal women, the estimated β and 95 % CI of sex hormone levels for the effect of solid fuel users was -0.337 (-0.657, -0.017), -0.233 (-0.47, 0.005), and - 0.240 (-0.452, -0.028) respectively, and - 0.150 (-0.296, -0.004) in ln-progesterone among postmenopausal women. It was found that combining solid fuels with long cooking periods or no ventilation more effectively reduced testosterone and androstenedione in premenopausal women. We further found the adverse effects of using solid fuel on progesterone, testosterone, and androstenedione levels were enhanced with the increases of PM1, PM2.5, PM10, and NO2. Corresponding genetic, the causal risk effect of solid fuel were - 0.056 (-0.513, 0.4) and 0.026 (-3.495, 3.547) for testosterone levels and sex hormone binding globulin, respectively.

CONCLUSION

Using gas or solid fuel was negatively related to sex hormone levels. A combination of using solid fuels, cooking for a long time, or cooking without ventilation had a stronger effect on sex hormone levels. However, genetic evidence did not support causality for the associations. WHAT IS ALREADY KNOWN ON THIS TOPIC?: The mechanisms underlying these associations household air pollution (HAP) from incomplete combustion of such fuels and occurrence of chronic diseases remained obscure. Recent years, extensive evidences from animal as well as human researches have suggested that progestogen and androgen hormones are involved in the development of diabetes, hypertension, and cardiovascular disease, which indicated that changes in serum progestogen and androgen hormones levels might play a role in these pathological mechanisms. However, limited evidence exists examining the effect of HAP from solid fuel use on serum sex hormone levels.

FUNDC1-mediated mitophagy triggered by mitochondrial ROS is partially involved in 1-nitropyrene-evoked placental progesterone synthesis inhibition and intrauterine growth retardation in mice

Intrauterine growth retardation (IUGR) is a major cause of perinatal morbidity and mortality. Previous studies showed that 1-nitropyrene (1-NP), an atmospheric pollutant, induces placental dysfunction and IUGR, but the exact mechanisms remain uncertain. In this research, we aimed to explore the role of mitophagy on 1-NP-evoked placental progesterone (P4) synthesis inhibition and IUGR in a mouse model. As expected, P4 levels were decreased in 1-NP-exposed mouse placentas and maternal sera. Progesterone synthases, CYP11A1 and 3βHSD1, were correspondingly declined in 1-NP-exposed mouse placentas and JEG-3 cells. Mitophagy, as determined by LC3B-II elevation and TOM20 reduction, was evoked in 1-NP-exposed JEG-3 cells. Mdivi-1, a specific mitophagy inhibitor, relieved 1-NP-evoked downregulation of progesterone synthases in JEG-3 cells. Additional experiments showed that ULK1/FUNDC1 signaling was activated in 1-NP-exposed JEG-3 cells. ULK1 inhibitor or FUNDC1-targeted siRNA blocked 1-NP-induced mitophagy and progesterone synthase downregulation in JEG-3 cells. Further analysis found that mitochondrial reactive oxygen species (ROS) were increased and GCN2 was activated in 1-NP-exposed JEG-3 cells. GCN2iB, a selective GCN2 inhibitor, and MitoQ, a mitochondria-targeted antioxidant, attenuated GCN2 activation, FUNDC1-mediated mitophagy, and downregulation of progesterone synthases in JEG-3 cells. In vivo, gestational MitoQ supplement alleviated 1-NP-evoked reduction of placental P4 synthesis and IUGR. These results suggest that FUNDC1-mediated mitophagy triggered by mitochondrial ROS may contribute partially to 1-NP-induced placental P4 synthesis inhibition and IUGR.

The Cytotoxic Effects of Fine Particulate Matter (PM2.5) from Different Sources at the Air-Liquid Interface Exposure on A549 Cells

The health of humans has been negatively impacted by PM2.5 exposure, but the chemical composition and toxicity of PM2.5 might vary depending on its source. To investigate the toxic effects of particulate matter from different sources on lung epithelial cells (A549), PM2.5 samples were collected from residential, industrial, and transportation areas in Nanjing, China. The chemical composition of PM2.5 was analyzed, and toxicological experiments were conducted. The A549 cells were exposed using an air-liquid interface (ALI) exposure system, and the cytotoxic indicators of the cells were detected. The research results indicated that acute exposure to different sources of particulate matter at the air-liquid interface caused damage to the cells, induced the production of ROS, caused apoptosis, inflammatory damage, and DNA damage, with a dose-effect relationship. The content of heavy metals and PAHs in PM2.5 from the traffic source was relatively high, and the toxic effect of the traffic-source samples on the cells was higher than that of the industrial- and residential-source samples. The cytotoxicity of particulate matter was mostly associated with water-soluble ions, carbon components, heavy metals, PAHs, and endotoxin, based on the analysis of the Pearson correlation. Oxidative stress played an important role in PM2.5-induced biological toxicity.

Associations of long-term exposure to air pollution and green space with reproductive hormones among women undergoing assisted reproductive technology: A longitudinal study

Studies investigating the association between long-term exposure to air pollution (AP)/green space and female reproductive hormones are still limited. Furthermore, their interactive effects remain unclear. Our study sought to explore the separate and interactive impacts of AP/green space on reproductive hormones among women undergoing assisted reproductive technology. We measured estradiol (E2), progesterone (P), testosterone (T), and follicle-stimulating hormone (FSH) from the longitudinal assisted reproduction cohort in Anhui, China. The annual mean concentrations of air pollutants were calculated at the residential level. Normalized Difference Vegetation Index (NDVI) within 500-m represented green space exposure. To assess the effect of AP/green space on hormones, we employed multivariable linear mixed-effect models. Our results showed that each one-interquartile range (IQR) increment in particulate matter (PM2.5 and PM10) and sulfur dioxide (SO2) was associated with -0.03[-0.05, -0.01], -0.03[-0.05, -0.02], and -0.03[-0.05, -0.01] decrease in P. An IQR increase in PM2.5, PM10, SO2, and carbon monoxide (CO) was associated with a -0.16[-0.17, -0.15], -0.15[-0.16, -0.14], -0.15[-0.16, -0.14], and -0.12[-0.13, -0.11] decrease in T and a -0.31[-0.35, -0.27], -0.30[-0.34, -0.26], -0.26[-0.30, -0.22], and -0.21[-0.25, -0.17] decrease in FSH. Conversely, NDVI500-m was associated with higher levels of P, T, and FSH, with β of 0.05[0.02, 0.08], 0.06[0.04, 0.08], and 0.07[0.00, 0.14]. Moreover, we observed the "U" or "J" exposure-response curves between PM2.5, PM10, and SO2 concentrations and E2 and P levels, as well as "inverted-J" curves between NDVI500-m and T and FSH levels. Furthermore, we found statistically significant interactions of SO2 and NDVI500-m on E2 and P as well as CO and NDVI500-m on E2. These findings indicated that green space might mitigate the negative effects of SO2 on E2 and P, as well as the effect of CO on E2. Future research is needed to determine these findings and underlying mechanisms.

Hypoxia activation attenuates progesterone synthesis in goat trophoblast cells via NR1D1 inhibition of StAR expression†

Trophoblast plays a crucial role in gestation maintenance and embryo implantation, partly due to the synthesis of progesterone. It has been demonstrated that hypoxia regulates invasion, proliferation, and differentiation of trophoblast cells. Additionally, human trophoblasts display rhythmic expression of circadian clock genes. However, it remains unclear if the circadian clock system is present in goat trophoblast cells (GTCs), and its involvement in hypoxia regulation of steroid hormone synthesis remains elusive. In this study, immunofluorescence staining revealed that both BMAL1 and NR1D1 (two circadian clock components) were highly expressed in GTCs. Quantitative real-time PCR analysis showed that several circadian clock genes were rhythmically expressed in forskolin-synchronized GTCs. To mimic hypoxia, GTCs were treated with hypoxia-inducing reagents (CoCl2 or DMOG). Quantitative real-time PCR results demonstrated that hypoxia perturbed the mRNA expression of circadian clock genes and StAR. Notably, the increased expression of NR1D1 and the reduction of StAR expression in hypoxic GTCs were also detected by western blotting. In addition, progesterone secretion exhibited a notable decline in hypoxic GTCs. SR9009, an NR1D1 agonist, significantly decreased StAR expression at both the mRNA and protein levels and markedly inhibited progesterone secretion in GTCs. Moreover, SR8278, an NR1D1 antagonist, partially reversed the inhibitory effect of CoCl2 on mRNA and protein expression levels of StAR and progesterone synthesis in GTCs. Our results demonstrate that hypoxia reduces StAR expression via the activation of NR1D1 signaling in GTCs, thus inhibiting progesterone synthesis. These findings provide new insights into the NR1D1 regulation of progesterone synthesis in GTCs under hypoxic conditions.

Cellular mechanisms linking to outdoor and indoor air pollution damage during pregnancy

Pregnancies are a critical window period for environmental influences over the mother and the offspring. There is a growing body of evidence associating indoor and outdoor air pollution exposure to adverse pregnancy outcomes such as preterm birth and hypertensive disorders of pregnancy. Particulate matter (PM) could trigger oxi-inflammation and could also reach the placenta leading to placental damage with fetal consequences. The combination of strategies such as risk assessment, advise about risks of environmental exposures to pregnant women, together with nutritional strategies and digital solutions to monitor air quality can be effective in mitigating the effects of air pollution during pregnancy.

Mechanistic toxicity assessment of differently sized and charged polystyrene nanoparticles based on human placental cells

Nanoplastics, as emerging contaminants, may be degraded from microplastics and released into aquatic systems globally, which pose threats to human health via ingestion with food or water. Although plastic fragments have been isolated from placental tissues in pregnant women, little is known about the direct toxicity of nanoplastics on human placental cells that plays a critical role in maintaining healthy growth of fetus. This study explored the mechanistic toxicity of polystyrene nanoplastics (PS-NPs) with different sizes (25, 50, 100 and 500 nm) and surface charges (-NH₂, -COOH and unlabeled) on human placental cells. Results showed that PS-NPs had size- and surface charge-specific toxicity pattern. The smaller the PS-NP size was, the greater the toxicity induced on human placental cells. In terms of surface charges, NH₂-labeled PS-NPs caused greater effects on cytotoxicity, inhibition of protein kinase A (PKA) activity, oxidative stress, and cell cycle arrest compared to COOH-labeled and unmodified PS-NPs. PS-NPs also induced size- and surface charge-dependent expression profiles of genes involved in various and interrelated toxicity pathways. In particular, PS-NPs increased intracellular reactive oxygen species in human placental cells, which can induce DNA damage and lead to cell cycle arrest in G1or G2 phase, inflammation and apoptosis. Our findings provide empirical evidences that the negative effects of nanoplastics on human placental cells, and highlight the necessity to conduct risk assessment of nanoplastics on female reproduction and fetal development.

Maternal steroids during pregnancy and their associations with ambient air pollution and temperature during preconception and early gestational periods

Hormones play critical roles in facilitating pregnancy progression and the onset of parturition. Several classes of environmental contaminants, including fine particulate matter (PM_2.5) and ambient temperature, have been shown to alter hormone biosynthesis or activity. However, epidemiologic research has not considered PM_2.5 in relation to a broader range of steroid hormones, particularly in pregnant women. Using metabolomics data collected within 20-40 weeks of gestation in an ethnically diverse pregnancy cohort study, we identified 42 steroid hormones that we grouped into five classes (pregnenolone, androgens, estrogens, progestin, and corticosteroids) based on their biosynthesis type. We found that exposure to PM_2.5 during the pre-conception and early prenatal periods was associated with higher maternal androgen concentrations in late pregnancy. We also detected a positive association between early pregnancy PM_2.5 exposure and maternal pregnenolone levels and a marginal positive association between early pregnancy PM_2.5 exposure and progestin levels. When considering each hormone metabolite individually, we found positive associations between early pregnancy PM_2.5 exposure and five steroids, two of which survived multiple comparison testing: 11beta-hydroxyandrosterone glucuronide (a pregnenolone steroid) and adrosteroneglucuronide (a progestin steroid). None of the steroid classes were statistically significant associated with ambient temperature. In sex-stratified analyses, we did not detect any sex differences in our associations. This is the first study showing that exposure to fine particulate matter during the pre-conception and early prenatal periods can lead to altered steroid adaptation during the state of pregnancy, which has been shown to have potential consequences on maternal and child health.

Mechanistic toxicity assessment of fine particulate matter emitted from fuel combustion via pathway-based approaches in human cells

Fuel exhaust particulate matter (FEPM) is an important source of air pollution worldwide. However, the comparative and mechanistic toxicity of FEPMs emitted from combustion of different fuels is still not fully understood. This study employed pathway-based approaches via human cells to evaluate mechanistic toxicity of FEPMs. The results showed that FEPMs caused concentration-dependent (0.1-200 μg/mL) cytotoxicity and oxidative stress. FEPMs at low concentration (10 μg/mL) induced cell cycle arrest in S and G2 phases, while high level of FEPMs (200 μg/mL) caused cell cycle arrest in G1 phase. Different FEPMs induced distinct expression profiles of toxicity-related genes, illustrating different toxic mechanisms. Furthermore, FEPMs inhibited the phosphorylation of protein kinase A (PKA), which related with reproductive toxicity. Spearman rank correlations among the chemicals carried by FEPMs and the toxic effects revealed that PAHs and metals promoted cell cycle arrest in the G1 phase and suppressed PKA activity. Furthermore, PAHs (Nap and Acy) and metals (Al and Pb) in FEPMs were highly and positively correlated with the expression of genes involved in apoptosis, ER stress, metal stress and inflammation. Our findings offered more mechanistic information of FEPMs at the level of subcellular toxicity and help to better understand their potential health effects.

SO2 derivatives induce dysfunction in human trophoblasts via inhibiting ROS/IL-6/STAT3 pathway

BACKGROUND

Epidemiological studies have revealed that sulfur dioxides (SO₂) can increase the risk of pregnancy complications such as missed abortion in the first trimester, stillbirth, preterm birth, small for gestational age, gestational diabetes mellitus and preeclampsia, but the mechanisms underlying these findings remains unknown. What is known, however, is that trophoblasts, a type of fetal cell exerting vital immunologic functions to maintain a successful pregnancy, are usually involved in the pathogenic mechanism of pregnancy complications.

OBJECTIVE

To study the effect of SO₂ derivatives (bisulfite and sulfite, 1:3 M/M) on the function of trophoblasts.

METHODS

Swan.71 trophoblast cells were treated with various concentrations of SO₂ derivatives to determine the effect of SO₂ derivatives on cellular viability by CKK8. Flow cytometry was performed to analyze the effect of SO₂ derivatives on apoptosis, cell cycle and intracellular ROS. Wound healing assay and transwell assay were conducted to examine the migration and invasion of Swan.71 cells. Inflammation-related cytokines in the supernatant (IL-1β, IL-6, IL-8, IL-10 and TNF-α) were measured by IMMULITE®1000 Systems (SIEMENS). The expression level of NLRP3, Caspase1, MMP9, MMP2, STAT3, and p-STAT3 were evaluated by Western Blotting.

RESULTS

Exposure to SO₂ derivatives significantly decreased cellular viability, arrested cell cycle at S/G2/M phase and induced cell apoptosis of Swan.71 trophoblasts. In addition, the migration and invasion of Swan.71 cell were significantly inhibited. SO₂ derivatives also significantly increased IL-1β secretion while it is NLRP3/Caspase1 independent. IL-6 secretion was significant inhibited accompanied by decreased STAT3 phosphorylation and expression of MMP2 and MMP9. The intracellular ROS level was significantly suppressed by SO₂ derivatives.

CONCLUSION

SO₂ derivatives exert toxic effects on trophoblasts which results in: suppressing cellular viability and intracellular ROS level, interfering with cell proliferation through arresting cell cycle, inducing cell apoptosis, disturbing inflammation-related cytokines secretion and inhibiting motility. Decreased ROS/IL-6/STAT3 levels play a role in inhibited cell viability, cell cycle arrest, apoptosis and defective motility.

Triphenyl phosphate causes a sexually dimorphic metabolism dysfunction associated with disordered adiponectin receptors in pubertal mice

The potential for triphenyl phosphate (TPhP) caused metabolic dysfunction has been documented. However, the relative mechanism of sexual dimorphic disruption on metabolism induced by TPhP remains unclear. Herein, we observed the insulin-sensitizing hormone (adiponectin) was inhibited in female serum while stimulated in males after oral administration of TPhP. Correspondingly, we found a high index of HOMA-IR in females. The primary receptors of adiponectin (AdipoR1 and AdipoR2) and the downstream: phosphorylation of AKT (pAKT) and PPAR⍺ signaling was attenuated in female liver. The disordered adiponectin/AdipoR signaling reduced hepatic glucose glycolysis and induced gluconeogenesis and finally led to the glucose intolerance in females. Also, the aberrant fatty acid β-oxidation and hepatic triacylglyceride (TG) deposition were found in female liver. Comparably, TPhP upregulated the AdipoR 1/2 and induced the downstream (pAMPK and PPAR⍺ signaling) in males. Thus, the serum glucose and hepatic TG level remained normal. However, modulation on AdipoR1/R2 and the genes related to glucose and lipid disposal in skeletal muscle has no gender-specific effect. Our research firstly revealed TPhP-induced hepatic nutrient metabolism was partially mediated by the adiponectin/AdipoR pathway in sexual-dependent manner during pubertal.

Maternal exposure to ambient fine particulate matter and risk of premature rupture of membranes in Wuhan, Central China: a cohort study

BACKGROUND

The associations between maternal exposure to ambient PM2.5 during pregnancy and the risk of premature rupture of membranes (PROM) and preterm premature rupture of membranes (PPROM) are controversial. And no relevant study has been conducted in Asia. This study aimed to determine the association between maternal exposure to ambient PM2.5 during pregnancy and the risk of (P)PROM.

METHODS

A cohort study including all singleton births in a hospital located in Central China from January 2015 through December 2017 was conducted. Multivariable logistic regression models, stratified analysis, generalized additive model, and two-piece-wise linear regression were conducted to evaluate how exposure to ambient PM2.5 during pregnancy is associated with the risks of PROM and PPROM.

RESULTS

A total of 4364 participants were included in the final analysis, where 11.71 and 2.34% of births were complicated by PROM and PPROM, respectively. The level of PM2.5 exhibited a degree of seasonal variation, and its median concentrations were 63.7, 59.3, 55.8, and 61.8 μg/m3 for the first trimester, second trimester, third trimester, and the whole duration of pregnancy, respectively. After adjustment for potential confounders, PROM was positively associated with PM2.5 exposure (per 10 μg/m3) [Odds Ratio (OR) = 1.14, 95% Confidence Interval (CI), 1.02-1.26 for the first trimester; OR = 1.09, 95% CI, 1.00-1.18 for the second trimester; OR = 1.13, 95% CI, 1.03-1.24 for the third trimester; OR = 1.35, 95% CI, 1.12-1.63 for the whole pregnancy]. PPROM had positive relationship with PM2.5 exposure (per 10 μg/m3) (OR = 1.17, 95% CI, 0.94-1.45 for first trimester; OR = 1.11, 95% CI, 0.92-1.33 for second trimester; OR = 1.19, 95% CI, 0.99-1.44 for third trimester; OR = 1.53, 95% CI, 1.03-2.27 for the whole pregnancy) Positive trends between the acute exposure window (mean concentration of PM2.5 in the last week and day of pregnancy) and risks of PROM and PPROM were also observed.

CONCLUSIONS

Exposure to ambient PM2.5 during pregnancy was associated with the risk of PROM and PPROM.

Ambient fine particulate matter induces inflammatory responses of vascular endothelial cells through activating TLR-mediated pathway

This study aims to investigate the role of Toll-like receptors (TLRs) on fine particulate matter (PM_2.5)-induced inflammatory responses of vascular endothelial cells. Inflammatory factors and TLRs were examined in the aorta of mice after nonsurgical intratracheal instillation of PM_2.5 as well as in the human umbilical vein endothelial cells (HUVECs) treated with PM_2.5. In addition, the effects of TLR2 and TLR4 inhibitors in the secretion of interleukin 6 (IL-6) and IL-1β and the expression of TLRs were determined in the HUVECs. The results showed that PM_2.5 could increase the expression of IL-1β, IL-6, TLR2, and TLR4 in vitro and in vivo. Anti-TLR2 IgG or TAK242, an inhibitor of TLR4, decreased the secretion of IL-1β and IL-6 by HUVECs and reduced the expression of corresponding TLRs. In conclusion, we demonstrate that both TLR2 and TLR4 are involved in PM_2.5-induced inflammatory responses of vascular endothelial cells. Inhibition of TLR2 and TLR4 expression has the potential to prevent PM_2.5-induced cardiovascular diseases.

Exposure of trophoblast cells to fine particulate matter air pollution leads to growth inhibition, inflammation and ER stress

Ambient air pollution is considered a major environmental health threat to pregnant women. Our previous work has shown an association between exposure to airborne particulate matter (PM) and an increased risk of developing pre-eclamspia. It is now recognized that many pregnancy complications are due to underlying placental dysfunction, and this tissue plays a pivotal role in pre-eclamspia. Recent studies have shown that PM can enter the circulation and reach the human placenta but the effects of PM on human placental function are still largely unknown. In this work we investigated the effects of airborne PM on trophoblast cells. Human, first trimester trophoblast cells (HTR-8/SV) were exposed to urban pollution particles (Malmö PM2.5; Prague PM10) for up to seven days in vitro and were analysed for uptake, levels of hCGβ and IL-6 secretion and proteomic analysis. HTR-8/SVneo cells rapidly endocytose PM within 30 min of exposure and particles accumulate in the cell in perinuclear vesicles. High doses of Prague and Malmö PM (500-5000 ng/ml) significantly decreased hCGβ secretion and increased IL-6 secretion after 48 h exposure. Exposure to PM (50 ng/ml) for 48h or seven days led to reduced cellular growth and altered protein expression. The differentially expressed proteins are involved in networks that regulate cellular processes such as inflammation, endoplasmic reticulum stress, cellular survival and molecular transport pathways. Our studies suggest that trophoblast cells exposed to low levels of urban PM respond with reduced growth, oxidative stress, inflammation and endoplasmic reticulum stress after taking up the particles by endocytosis. Many of the dysfunctional cellular processes ascribed to the differentially expressed proteins in this study, are similar to those described in PE, suggesting that low levels of urban PM may disrupt cellular processes in trophoblast cells. Many of the differentially expressed proteins identified in this study are involved in inflammation and may be potential biomarkers for PE.

Impact of ambient PM2.5 on adverse birth outcome and potential molecular mechanism

PM_2.5 (particulate matter ≤2.5 µm in aerodynamic diameter) refers to atmospheric particulate matter (PM) with an aerodynamic diameter of equal and less than 2.5 µm that tends to be suspended for long periods of time and travel over long distances in both outdoor and indoor atmospheres. PM_2.5, along with the toxic compounds attached on it, may cause a wide range of disorders. The fetus is considered to be highly susceptible to a variety of toxicants including atmospheric pollutants such as PM_2.5 through prenatal exposure. To better understand the relationship between maternal exposure to PM_2.5 and adverse birth outcomes for reproduction and fetus development, we studied the published data on this issue including case-control studies, cohort studies and meta-analyses studies, and summarized the basic impact of ambient particulate matter on adverse birth outcomes. Research evidence indicates that PM_2.5 has a potential to induce low birth weight (LBW), preterm birth (PTB), and stillbirth. A further in-depth analysis shows that oxidative stress, DNA methylation, mitochondrial DNA (mtDNA) content alteration, and endocrine disruptions may all play an important role in PM_2.5 induced adverse effects to pregnant women and fetuses. In addition, PM_2.5 exposure can cause male reproductive toxicity, leading to associated adverse pregnancy outcomes.

Physiology and Pathophysiology of Steroid Biosynthesis, Transport and Metabolism in the Human Placenta

The steroid hormones progestagens, estrogens, androgens, and glucocorticoids as well as their precursor cholesterol are required for successful establishment and maintenance of pregnancy and proper development of the fetus. The human placenta forms at the interface of maternal and fetal circulation. It participates in biosynthesis and metabolism of steroids as well as their regulated exchange between maternal and fetal compartment. This review outlines the mechanisms of human placental handling of steroid compounds. Cholesterol is transported from mother to offspring involving lipoprotein receptors such as low-density lipoprotein receptor (LDLR) and scavenger receptor class B type I (SRB1) as well as ATP-binding cassette (ABC)-transporters, ABCA1 and ABCG1. Additionally, cholesterol is also a precursor for placental progesterone and estrogen synthesis. Hormone synthesis is predominantly performed by members of the cytochrome P-450 (CYP) enzyme family including CYP11A1 or CYP19A1 and hydroxysteroid dehydrogenases (HSDs) such as 3β-HSD and 17β-HSD. Placental estrogen synthesis requires delivery of sulfate-conjugated precursor molecules from fetal and maternal serum. Placental uptake of these precursors is mediated by members of the solute carrier (SLC) family including sodium-dependent organic anion transporter (SOAT), organic anion transporter 4 (OAT4), and organic anion transporting polypeptide 2B1 (OATP2B1). Maternal-fetal glucocorticoid transport has to be tightly regulated in order to ensure healthy fetal growth and development. For that purpose, the placenta expresses the enzymes 11β-HSD 1 and 2 as well as the transporter ABCB1. This article also summarizes the impact of diverse compounds and diseases on the expression level and activity of the involved transporters, receptors, and metabolizing enzymes and concludes that the regulatory mechanisms changing the physiological to a pathophysiological state are barely explored. The structure and the cellular composition of the human placental barrier are introduced. While steroid production, metabolism and transport in the placental syncytiotrophoblast have been explored for decades, few information is available for the role of placental-fetal endothelial cells in these processes. With regard to placental structure and function, significant differences exist between species. To further decipher physiologic pathways and their pathologic alterations in placental steroid handling, proper model systems are mandatory.