Cytotoxicant-induced trophoblast dysfunction and abnormal pregnancy outcomes: role of zinc and metallothionein

Effects of heavy metal exposure during pregnancy on birth outcomes

Exposure to heavy metals such as lead, cadmium, and mercury poses serious health risks to pregnant women because of their high toxicity. In this study, we investigated the associations of heavy metal exposure with birth outcomes of Korean infants. Data of 5,215 women between 2015 and 2019 were analyzed. This study was part of the Korean Children's Environmental Health (Ko-CHENS) study. Linear regression and logistic regression analyses were used to examine effects of concentrations of lead, cadmium, and mercury on birth weight, small for gestational age, and large for gestational age after adjusting for maternal age groups, parity, infant sex, education, income, smoking, drinking, body mass index, stillbirth, premature birth, diabetes, hypertension, and gestational diabetes. Besides adjusting for these covariates, each metal was mutually adjusted to estimate birth weight and large for gestational age status. Maternal cadmium concentrations during early pregnancy (β =  - 39.96; 95% confidence interval (CI): - 63.76, - 16.17) and late pregnancy (β =  - 37.24; 95% CI - 61.63, - 12.84) were significantly associated with birth weight. Cadmium levels during early pregnancy (adjusted OR = 0.637; 95% CI 0.444, 0.912) were also associated with large for gestational age status. Our findings suggest that prenatal cadmium exposure, even at a low level of exposure, is significantly associated with low birth weight.

TGF-β1 alleviates HgCl2 induced apoptosis via P38 MAPK signaling pathway in human trophoblast cells

It is well known that embryonic development can be perturbed by environmental factors such as heavy metals. Mercury is one of the most significant threats to the environment and human health. Mercury can damage many parts of the human body, including lungs, kidneys, nerves and fetus. However, the effect of mercury on human embryo remains unknown. Here, we showed that HgCl₂ treatment resulted in a significant increase in apoptosis in HTR-8/SVneo cells. However, the effect of HgCl₂ on apoptosis was partially reduced by the combination treatment with TGF-β1 and HgCl₂ in HTR-8/SVneo cells. Moreover, HgCl₂ treatment gradually decreased the expression of TGF-β1 in a dose dependent manner. Furthermore, a P38 MAPK inhibitor, SB202190, decreased the cell apoptosis and caspase activation induced by HgCl₂ in trophoblast cells. In addition, TGF-β1 alleviated HgCl₂ induced apoptosis of HTR-8/SVneo cells via p38 MAPK signaling pathway, which was involved in the TAK1 expression. These results might provide a theoretical basis for mercury induced trophoblast associated embryo damage and a potential avenue of intervention.

Nifedipine Prevents Apoptosis of Alcohol-Exposed First-Trimester Trophoblast Cells

BACKGROUND

Maternal alcohol abuse leading to fetal alcohol spectrum disorder (FASD) includes fetal growth restriction (FGR). Ethanol (EtOH) induces apoptosis of human placental trophoblast cells, possibly disrupting placentation and contributing to FGR in FASD. EtOH facilitates apoptosis in several embryonic tissues, including human trophoblasts, by raising intracellular Ca²⁺ . We previously found that acute EtOH exposure increases trophoblast apoptosis due to signaling from both intracellular and extracellular Ca²⁺ . Therefore, nifedipine, a Ca²⁺ channel blocker that is commonly administered to treat preeclampsia and preterm labor, was evaluated for cytoprotective properties in trophoblast cells exposed to alcohol.

METHODS

Human first-trimester chorionic villous explants and the human trophoblast cell line HTR-8/SVneo (HTR) were pretreated with 12.5 to 50 nM of the Ca²⁺ channel blocker nifedipine for 1 hour before exposure to 50 mM EtOH for an additional hour. Intracellular Ca²⁺ concentrations were monitored in real time by epifluorescence microscopy, using fluo-4-AM. Apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), accumulation of cytoplasmic cytochrome c, and cleavage rates of caspase 3 and caspase 9.

RESULTS

The increase in intracellular Ca²⁺ upon exposure to EtOH in both villous explants and HTR cells was completely blocked (p < 0.05) when pretreated with nifedipine, accompanied by inhibition of EtOH-induced release of cytochrome c, caspase activities, and TUNEL.

CONCLUSIONS

This study indicates that nifedipine can interrupt the apoptotic pathway downstream of EtOH exposure and could provide a novel strategy for future interventions in women with fetuses at risk for FASD.

Unravelling the Role of Metallothionein on Development, Reproduction and Detoxification in the Wall Lizard Podarcis sicula

Metallothioneins (MTs) are an evolutionary conserved multigene family of proteins whose role was initially identified in binding essential metals. The physiological role of MT, however, has been revealed to be more complex than expected, since not only are MTs able to bind to toxic heavy metals, but many isoforms have shown specialized and alternative functions. Within this uncertainty, the information available on MTs in non-mammalian vertebrates, particularly in neglected tetrapods such as the reptiles, is even more scant. In this review, we provide a summary of the current understanding on metallothionein presence and function in the oviparous lizard Podarcis sicula, highlighting the results obtained by studying MT gene expression in most representative adult and embryonic tissues. The results demonstrate that in adults, cadmium induces MT transcription in a dose- and tissue-specific manner. Thus, the MT mRNAs appear, at least in some cases, to be an unsuitable tool for detecting environmental ion contamination. In early embryos, maternal RNAs sustain developmental needs for MT protein until organogenesis is well on its way. At this time, transcription starts, but again in a tissue- and organ-specific manner, suggesting an involvement in alternative roles. In conclusion, the spatiotemporal distribution of transcripts in adults and embryos definitively confirms that MT has deserved the title of elusive protein.

Triazole fungicide tebuconazole disrupts human placental trophoblast cell functions

Triazole fungicides are one of the top ten classes of current-use pesticides. Although exposure to triazole fungicides is associated with reproductive toxicity in mammals, limited information is available regarding the effects of triazole fungicides on human placental trophoblast function. Tebuconazole (TEB) is a common triazole fungicide that has been extensively used for fungi control. In this work, we showed that TEB could reduce cell viability, disturb normal cell cycle distribution and induce apoptosis of human placental trophoblast cell line HTR-8/SVneo (HTR-8). Bcl-2 protein expression decreased and the level of Bax protein increased after TEB treatment in HTR-8 cells. The results demonstrated that this fungicide induced apoptosis of trophoblast cells via mitochondrial pathway. Importantly, we found that the invasive and migratory capacities of HTR-8 cells decreased significantly after TEB administration. TEB altered the expression of key regulatory genes involved in the modulation of trophoblast functions. Taken together, TEB suppressed human trophoblast invasion and migration through affecting the expression of protease, hormones, angiogenic factors, growth factors and cytokines. As the invasive and migratory abilities of trophoblast are essential for successful placentation and fetus development, our findings suggest a potential risk of triazole fungicides to human pregnancy.

Differential proteomic expression of human placenta and fetal development following e-waste lead and cadmium exposure in utero

Prenatal exposure to lead (Pb) and cadmium (Cd) has been associated with a series of physiological problems resulting in fetal growth restriction. We aimed to investigate the effects of Pb and Cd exposure on placental function and the potential mechanisms involved in fetal development. Placental specimens and questionnaires were collected from an e-waste area and a reference area in China. Two-dimensional electrophoresis combined with MALDI-TOF-MS/MS and molecular network relationship were performed to analyze differentially expressed proteins using a compositing sample pool. Compared with the reference group, the exposed group exhibited significantly higher levels of placental Pb and Cd (p<0.01), shorter body length and higher gestational age (p<0.01). After bivariate adjustment in a linear regression model, decreases of 205.05g in weight and 0.44cm in body length were associated with a 10ng/g wt increase in placental Cd. Pb showed a negative trend but lacked statistical significance. Proteomic analysis showed 32 differentially-expressed proteins and were predominantly involved in protein translocation, cytoskeletal structure, and energy metabolism. Fumarate hydratase was down-regulated in the exposed placenta tissues and validated by ELISA. Alterations in placental proteome suggest that imbalances in placental mitochondria respiration might be a vital pathway targeting fetal growth restriction induced by exposure to Cd.

Effect of microcystin-LR on human placental villous trophoblast differentiation in vitro

Microcystin-LR is a cyanobacterial toxin found in surface and recreational waters that inhibits protein phosphatases and may disrupt the cytoskeleton. Microcystins induce apoptosis in hepatocytes at ≤ 2.0 µM. Nothing is known about the effects of microcystins on human placental trophoblast differentiation and function. The differentiation of villous trophoblasts to form syncytiotrophoblast occurs throughout pregnancy and is essential for normal placental and fetal development. To investigate the effects of microcystin, villous cytotrophoblasts were isolated from term placentas using an established method and exposed to microcystin-LR. Microcystin-LR below the cytotoxic dose of 25 µM did not cause cell rounding or detachment, had no effect on apoptosis, and no effect on the morphological differentiation of mononucleated cytotrophoblasts to multinucleated syncytiotrophoblast. However, secretion of human chorionic gonadotropin (hCG) increased in a microcystin-LR dose-dependent manner. When incubated with l-buthionine sulphoximine (BSO) to deplete glutathione levels, trophoblast morphological differentiation proceeded normally in the presence of microcystin-LR. Microcystin-LR did not disrupt the trophoblast microtubule cytoskeleton, which is known to play a role in trophoblast differentiation. Immunofluorescence studies showed that trophoblasts express organic anion transport protein 1B3 (OATP1B3), a known microcystin transport protein. In comparison to hepatocytes, trophoblasts appear to be more resistant to the toxic effects of microcystin-LR. The physiological implications of increased hCG secretion in response to microcystin-LR exposure remain to be determined.

The shared pathoetiological effects of particulate air pollution and the social environment on fetal-placental development

Exposure to particulate air pollution and socioeconomic risk factors are shown to be independently associated with adverse pregnancy outcomes; however, their confounding relationship is an epidemiological challenge that requires understanding of their shared etiologic pathways affecting fetal-placental development. The purpose of this paper is to explore the etiological mechanisms associated with exposure to particulate air pollution in contributing to adverse pregnancy outcomes and how these mechanisms intersect with those related to socioeconomic status. Here we review the role of oxidative stress, inflammation and endocrine modification in the pathoetiology of deficient deep placentation and detail how the physical and social environments can act alone and collectively to mediate the established pathology linked to a spectrum of adverse pregnancy outcomes. We review the experimental and epidemiological literature showing that diet/nutrition, smoking, and psychosocial stress share similar pathways with that of particulate air pollution exposure to potentially exasperate the negative effects of either insult alone. Therefore, socially patterned risk factors often treated as nuisance parameters should be explored as potential effect modifiers that may operate at multiple levels of social geography. The degree to which deleterious exposures can be ameliorated or exacerbated via community-level social and environmental characteristics needs further exploration.

Apoptosis of alcohol-exposed human placental cytotrophoblast cells is downstream of intracellular calcium signaling

BACKGROUND

Apoptosis is induced by ethanol (EtOH) in human placental trophoblast cells, possibly disrupting placentation and contributing to intrauterine growth restriction in fetal alcohol spectrum disorder (FASD). EtOH induces programmed cell death in several embryonic tissues by raising intracellular Ca(2+) . Therefore, the role of Ca(2+) signaling in EtOH-induced apoptosis was examined using human first trimester cytotrophoblast cell lines, examining the hypothesis that apoptosis is dependent on intracellular Ca(2+) signaling.

METHODS

Using HTR-8/SVneo and SW.71 cytotrophoblast cell lines, real-time intracellular Ca(2+) concentration was monitored by fluo-4 epifluorescence microscopy and apoptosis was assessed by flow cytometry of cells fluorescently labeled for DNA fragmentation (TUNEL) and annexin V binding.

RESULTS

Intracellular Ca(2+) concentrations increased synchronously in all cells within 10 seconds of exposure to 50 mM EtOH, but not at lower EtOH concentrations (10 to 25 mM) incapable of inducing apoptosis. Trophoblast cells treated with inhibitors of Ca(2+) signaling (BAPTA-AM, U73122, xestospongin D, BAPTA, SKF-96365) produced no intracellular Ca(2+) transients after exposure to 50 mM EtOH and were protected from cell death induced by EtOH.

CONCLUSIONS

EtOH-induced apoptosis in human cytotrophoblast cells, identified by DNA fragmentation and externalized phosphatidylserine, was dependent upon Ca(2+) signaling. Both intracellular Ca(2+) mobilization and extracellular Ca(2+) influx were required, as well as phosphatidylinositol signaling. Inhibition by SKF-96365 suggests that the capacitative Ca(2+) entry mechanism that utilizes TRPC channels was activated by EtOH. Apoptosis occurs downstream of Ca(2+) signaling in trophoblasts and may contribute to placental insufficiency and poor fetal growth associated with FASD.

Could zinc prevent reproductive alterations caused by cigarette smoke in male rats?

The aim of the present study was to evaluate the effects of zinc on fertility through semen parameters, testosterone level and oxidative DNA damage to spermatozoa of rats exposed to cigarette smoke. Male Wistar rats (60 days old) were divided into four groups (n = 10 per group): control, cigarette-smoking (20 cigarettes per day), zinc (zinc chloride 20 mg kg–1 day–1) and zinc plus cigarette-smoking (zinc chloride 20 mg kg–1 day–1; 20 cigarettes per day). The treatment was applied for nine weeks and the following parameters were analysed: bodyweight, wet weights of the reproductive organs and the adrenal gland, plasma testosterone concentration, testicular function (seminal analysis and daily sperm production) and sperm DNA oxidative damage. The exposure to cigarette smoke decreased testosterone concentration, the percentage of normal morphology and the motility of spermatozoa. In addition, this exposure increased sperm DNA oxidative damage. Zinc treatment protected against the toxic damage that smoking caused to spermatozoa. This study showed a correlation between smoking and possible male infertility and subfertility, and also that the majority of smoking-induced changes in spermatozoa were prevented by zinc treatment. In conclusion, zinc, an antioxidant and stimulant of cell division, can be indicated as a promising treatment in men with infertility caused by the toxic components of cigarette smoke.

Cardiac-specific overexpression of metallothionein rescues nicotine-induced cardiac contractile dysfunction and interstitial fibrosis

Cigarette smoking is a devastating risk factor for cardiovascular diseases and nicotine is believed the main toxin component responsible for the toxic myocardial effects of smoking. Nonetheless, neither the precise mechanism of nicotine-induced cardiac dysfunction nor effective treatment is elucidated. The aim of this study was to evaluate the impact of cardiac-specific overexpression of heavy metal scavenger metallothionein on myocardial geometry and mechanical function following nicotine exposure. Adult male friend virus B (FVB) wild-type and metallothionein mice were injected with nicotine (2 mg/kg/d) intraperitoneally for 10 days. Mechanical and intracellular Ca²+ properties were examined. Myocardial histology (cross-sectional area and fibrosis) was evaluated by hematoxylin and eosin (H&E) and Masson trichrome staining, respectively. Oxidative stress and apoptosis were measured by fluoroprobe 5-(6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H₂DCFDA) fluorescence and caspase-3 activity, respectively. Nicotine exposure failed to affect the protein abundance of metallothionein. Our data revealed reduced echocardiographic contractile capacity (fractional shortening), altered cardiomyocyte contractile and intracellular Ca²+ properties including depressed peak shortening amplitude, maximal velocity of shortening/relengthening, resting and electrically-stimulated rise in intracellular Ca²+, as well as prolonged duration of relengthening and intracellular Ca²+ clearance in hearts from nicotine-treated FVB mice, the effect of which was ameliorated by metallothionein. Biochemical and histological findings depicted overt accumulation of reactive oxygen species (ROS), apoptosis and myocardial fibrosis without any change in myocardial cross-sectional area following nicotine treatment, which was mitigated by metallothionein. Taken together, our findings suggest the antioxidant metallothionein may reconcile short-term nicotine exposure-induced myocardial contractile dysfunction and fibrosis possibly through inhibition of ROS accumulation and apoptosis.

Maternal and fetal exposure to four carcinogenic environmental metals

OBJECTIVE

To examine maternal and fetal exposure levels to four carcinogenic metals, arsenic (As), cadmium (Cd), nickel (Ni), and beryllium (Be), and to investigate their environmental influences.

METHODS

Metal concentrations in maternal and umbilical cord blood were measured by inductively coupled plasma-mass spectrometry (ICP-MS). Environmental factors that might play a role in exposure were analyzed using Mann-Whitney nonparametric U-tests and multiple linear regression.

RESULTS

The concentrations of As, Cd, and Ni in umbilical cord blood (5.41, 0.87, and 139.54 μg/L) were significantly lower than those in maternal blood (6.91, 1.93, and 165.93 μg/L). There were significant positive correlations between the maternal and cord concentrations of each carcinogen. Our results showed that: (i) exposures to potentially harmful occupational factors during pregnancy were associated with high levels of maternal As, Cd, and Ni; (ii) living close to major transportation routes (<500 m) or exposure to second-hand smoke during pregnancy increased the maternal Cd levels and (iii) living close to industrial chimneys induced high maternal Ni levels. Multiple linear regression analysis showed that these environmental factors remained significant in models of the influences of these four carcinogens.

CONCLUSION

Both mothers and fetuses had been exposed to As, Cd, Ni, and Be. The increased levels of these carcinogens in pregnant women were associated with some detrimental environmental factors, such as occupational exposure, contact with second-hand smoke and living close to major transportation routes or industrial chimneys.

Ultrastructural changes in the kidney of rats with acute exposure to cadmium and effects of exogenous metallothionein

Ultrastructural changes in the kidneys of rats after acute cadmium exposure and the effects of exogenous metallothionein (MT) were studied by transmission electron microscopy. Thirty-six adult Wistar rats were divided into three groups. Cadmium chloride (CdCl2) (3.5 mg/kg/day) was injected subcutaneously in the first group. In the second group, 30 micromol/kg MT was administered in addition to CdCl2. Control rats received 0.5 ml subcutaneous saline solution. Four rats from each group were killed on days 1, 3, 5, and 7 after administration of the compounds. Kidney tissues were taken and fixed in 2.5% glutaraldehyde solution for electron microscopic observations. Tissue damage in kidney increased as time passed since the administration of CdCl2 in the first group. Degeneration in the proximal and distal tubules was observed. Increased apoptosis was seen in the proximal tubules epithelium, especially on day 7. Peritubular capillaries became dilated, there was degeneration of the endothelial cells, and the amount of intertubular collagen fibers was increased. On day 1, irregular microvilli in the proximal tubules, deepening of the basal striations, and myelin figures; on day 3, multiple vesicular mitochondria and regions of edema around tubules; on days 5 and 7, increased apoptotic cell in the proximal tubules and widened rough endoplasmic reticulum of the endothelial cells of glomerular capillaries were observed. We observed that the structural alterations that increased depending on the day of Cd administration decreased after exogenous MT administration, the dilation of the peritubular capillaries persisted, and there were degenerated proximal tubules. It was established that cadmium chloride was toxic for kidney cortex and caused structural damage. Exogenous MT partly prevents CdCl2-induced damage.

Morphological and biological effects of maternal exposure to tobacco smoke on the feto-placental unit

Active and passive maternal smoking has a damaging effect in every trimester of human pregnancy. Cigarette smoke contains scores of toxins which exert a direct effect on the placental and fetal cell proliferation and differentiation and can explain the increased risk of miscarriage, fetal growth restriction (FGR) stillbirth, preterm birth and placental abruption reported by epidemiological studies. In the placenta, smoking is associated from early in pregnancy, with a thickening of the trophoblastic basement membrane, an increase in collagen content of the villous mesenchyme and a decrease in vascularisation. These anatomical changes are associated with changes in placental enzymatic and synthetic functions. In particular, nicotine depresses active amino-acid (AA) uptake by human placental villi and trophoblast invasion and cadmium decreases the expression and activity of 11 beta-hydroxysteroid dehydrogenase type 2 which is causally linked to FGR. Maternal smoking also dysregulates trophoblast expression of molecules that govern cellular responses to oxygen tension. In the fetus, smoking is associated with a reduction of weight, fat mass and most anthropometric parameters and as in the placenta with alterations in protein metabolism and enzyme activity. These alterations are the results of a direct toxic effect on the fetal cells or an indirect effect through damage to, and/or functional disturbances of the placenta. In particular, smoking interferes strongly with the fetal brain and pancreas biological parameters and induces chromosomal instability, which is associated with an increase in the risk of cancer, especially childhood malignancies.

Control of human trophoblast function

The trophoblast, i.e. the peripheral part of the human conceptus, exerts a crucial role in implantation and placentation. Both processes properly occur as a consequence of an intimate dialogue between fetal and maternal tissues, fulfilled by membrane ligands and receptors, as well as by hormone and local factor release. During blastocyst implantation, generation of distinct trophoblast cell types begins, namely the villous and the extravillous trophoblast, the former of which is devoted to fetal-maternal exchanges and the latter binds the placental body to the uterine wall. Physiological placentation is characterized by the invasion of the uterine spiral arteries by extravillous trophoblast cells arising from anchoring villi. Due to this invasion, the arterial structure is replaced by amorphous fibrinoid material and endovascular trophoblastic cells. This transformation establishes a low-resistance, high-capacity perfusion system from the radial arteries to the intervillous space, in which the villous tree is embedded. The physiology of pregnancy depends upon the orderly progress of structural and functional changes of villous and extravillous trophoblast, whereas a derangement of such processes can lead to different types of complications of varying degrees of gravity, including possible pregnancy loss and maternal life-threatening diseases. In this review we describe the mechanisms which regulate trophoblast differentiation, proliferation, migration and invasiveness, and the alterations in these mechanisms which lead to pathological conditions. Furthermore, based on the growing evidence that proper inflammatory changes and oxidative balance are needed for successful gestation, we explain the mechanisms by which agents able to influence such processes may be useful in the prevention and treatment of pregnancy disorders.

Cadmium reduces 11 beta-hydroxysteroid dehydrogenase type 2 activity and expression in human placental trophoblast cells

Cadmium, a common environmental pollutant and a major constituent of tobacco smoke, has been identified as a new class of endocrine disruptors with a wide range of detrimental effects on mammalian reproduction. During human pregnancy, maternal cadmium exposure, via the environment and/or cigarette smoking, leads to fetal growth restriction (FGR), but the underlying mechanisms are unknown. Although a substantial amount of evidence suggests that cadmium may affect fetal growth indirectly via the placenta, the molecular targets remain to be identified. Given that reduced placental 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2, encoded by HSD11B2 gene) is causally linked to FGR, the present study was undertaken to examine the hypothesis that cadmium induces FGR in part by targeting placental HSD11B2. Using cultured human trophoblast cells as a model system, we showed that cadmium exposure resulted in a time- and concentration-dependent decrease in 11 beta-HSD2 activity, such that an 80% reduction was observed after 24-h treatment at 1 microM. It also led to a similar decrease in levels of 11 beta-HSD2 protein and mRNA, suggesting that cadmium reduced 11 beta-HSD2 expression. Furthermore, cadmium diminished HSD11B2 promoter activity, indicative of repression of HSD11B2 gene transcription. In addition, the effect of cadmium was highly specific, in that other divalent metals (Zn(2+), Mg(2+), and Mn(2+)) as well as nicotine and cotinine (a major metabolite of nicotine) did not alter 11 beta-HSD2 activity. Taken together, these findings demonstrate that cadmium reduces human placental 11 beta-HSD2 expression and activity by suppressing HSD11B2 gene transcription. Thus the present study identifies placental 11 beta-HSD2 as a novel molecular target of cadmium. It also reveals a molecular mechanism by which this endocrine disruptor may affect human placental function and, consequently, fetal growth and development.