Purification of metallothionein-like protein in rat placenta

Human placental cell line HTR-8/SVneo accumulates cadmium by divalent metal transporters DMT1 and ZIP14

Cadmium (Cd) is a global pollutant that accumulates in the placenta and can cause placental dysfunction. Although iron transporters have been suggested to participate in placental Cd uptake, it is still unknown which transporters are actually involved in this process. We specifically aimed to study the role of three iron transporters in the uptake of Cd into the placental cell line HTR-8/SVneo. For this purpose, Divalent Metal Transporter (DMT)1 and ZRT/IRT like protein (ZIP)8 and ZIP14 were downregulated and changes in cellular Cd levels analysed in relation to controls. As clearly shown by the reduction of the Cd content by ∼60% in DMT1- and ZIP14-downregulated cells, the two proteins are essential for Cd accumulation in HTR-8/SVneo cells. Using a validated antibody, we show DMT1 to be localised in situ in trophoblast and stromal cells. We further wanted to investigate how placental cells cope with Cd loading and which metallothionein (MT) isoforms they express. Cd-exposed cells accumulate Cd in a dose-dependent manner and upregulate MT2A accordingly (up to 15-fold induction upon 5 μM CdCl₂ treatment for 72 h). 5 μM Cd exposure for 72 h decreased cell number to 60%, an effect that was aggravated by MT2A depletion (cell number reduced to 30%) indicating additive effects. In conclusion, our data suggest that DMT1 and ZIP14 are required for Cd uptake into human placental cells that upregulate MT2A to store and detoxify the metal. Cd storage in the placenta reduces Cd transport to the fetus, which, however, could impair placental functions and fetal development.

Effect of gestational and lactational exposure to lead and/or cadmium on reproductive performance and hepatic oestradiol metabolising enzymes

Adult female rats were treated subcutaneously (0.05 mg/kg body wt./day) with lead acetate and cadmium acetate separately and in combination during the gestational and lactational periods with a pre-exposure before mating. No change in the reproductive cyclicity was observed in any of the treated groups. The number of pregnancies was similar in all groups and no effect was observed on reproductive performance. The litter size, placental weights, pup weights, pup liver weights, maternal weights or maternal liver weights did not differ significantly. The activities of hepatic steroid metabolising enzyme 17-beta-hydroxy steroid oxidoreductase and of UDP glucoronyl transferase were decreased and the hepatic cytochrome P450 (CYP450) content was reduced by the metal exposure. Hepatic DNA and glycogen content were decreased in the cadmium and the combined treated groups in both lactating mother and pups at post-natal day 21 (PND 21). Lead and cadmium accumulated in the liver of the metal treated pregnant and lactating rats. The accumulation of the metals was also observed in foetal and pups (PND 21). Hepatic zinc content was increased in the cadmium and the combined treated pregnant and lactating mothers whereas foetal and neonatal livers showed a decrease in the zinc as compared to control. The results of the study indicate that despite the ability of lead and cadmium to alter various biochemical parameters the effect in the liver is not intensified at combined exposure to both lead and cadmium. The observed biochemical alterations in the liver of rats co-exposed to lead and cadmium may result from an independent effect of lead and/or cadmium and also from their interaction. However, these results suggest that when lead and cadmium are administered together in similar concentrations, the major effects are mediated by cadmium.

Maternal-fetal distribution of cadmium in the guinea pig following a low dose inhalation exposure

Pregnant guinea pigs in their last trimester of gestation were exposed by inhalation to cadmium (Cd) chloride level (50 microg/m3 Cd) for 1 and 5 days. Cd content was evaluated by atomic absorption spectrophotometry. Maternal blood Cd concentration increased by 127 and 223% of control for 1 and 5 days of exposure. Maternal lung Cd concentration increased significantly by 11.66- and by 48.24-fold after 1 and 5 days of treatment, while maternal liver showed an increase of 188 and 227% for 1 and 5 days of exposure. Also, fetal Cd concentration significantly increased in brain (156 and 192%), liver (159 and 174%) and heart (201 and 157%) after 1 and 5 days of exposure, compared to unexposed females. Placental calcium content decreased significantly by 16% of control after 5 days of exposure. These results suggest that low-level inhalation of Cd may pass through the guinea pig placenta and accumulate in fetal brain, liver and heart.

Purification and characterization of a low molecular weight zinc binding protein from human placenta

A low molecular weight, native zinc binding, cytosolic protein (LMZP) has been isolated, purified and characterized from human normal term placenta. Gel filtration of heat treated placental cytosol after sequential acetone precipitation (80% ppt) revealed a major zinc binding protein in the range of low molecular weight. This partially purified zinc binding fraction was further fractionated on DEAE-Sephadex A-25. The zinc was eluted in one of the three peak fractions. Further, the purity of zinc binding protein was confirmed on fast protein liquid chromatography (FPLC). The purified placental LMZP was homogenous on SDS-polyacrylamide gel electrophoresis with a single band. Ultraviolet (UV) spectrum of LMZP showed an absorption maximum at 257 nm which disappeared at pH 2. Molecular weight of LMZP as determined by gel chromatography, SDS-polyacrylamide gel electrophoresis and amino acid analysis was 6 kDa. It was calculated that 1 g atom of zinc was bound to 1 mole of the LMZP. Unlike in classical metallothionein, the amino acid composition of placental LMZP revealed the presence of aromatic amino acids, lower content of cysteine and higher content of histidine, glutamic acid and aspartic acid (10, 9 and 5 residues/mole, respectively).

Transfer and accumulation of cadmium, and the level of metallothionein in perfused human placentae

The purpose of the present study was to investigate the effect of perfusion with a medium containing 12 or 24 micrograms Cadmium (as CdCl2) per ml on this metal's accumulation, transfer rate and metallothionein (MT) level. The experiments were performed with an isolated lobule of a dually-perfused human term placenta. Placental cell integrity and viability were characterised by their morphology and metabolic function, manifested in the tissue's electron microscopic structure and glucose and oxygen (O2) consumption, respectively. Perfusion with 24 micrograms Cd/ml medium for 5 h resulted in significant elevation in MT. The transfer rate of Cd to the fetal side of the placenta was very slow, and not until 40 min after the addition of Cd into the maternal side was a significant increase in the metal's level observed in the fetal perfusate. Thereafter, the level of the metal increased gradually and reached a steady state about 1 h later, at a level which was less than 1/20th of its concentration in the maternal perfusate. There was a 60-fold increase in Cd level in the cytosolic fraction obtained from the Cd-treated samples. At 12 micrograms Cd/ml no significant changes were noted in morphology, metabolic function and MT content. None of the Cd levels caused a significant change in O2 and glucose consumption, in spite of the fact that with the higher Cd dose the microstructure of the tissue showed some pathological changes. The observed elevation in MT may provide the fetus some protection against the harmful effects of the metal.

Cadmium effects and biochemical status in hamsters following acute exposure in late gestation

A normally teratogenic dose of cadmium ions administered to hamsters late in gestation does not cross the placental barrier nor does it result in placental pathology. Our finding, which differs from data for other rodents, may be due to differences in the chemical status of cadmium in the placental cytosols.

Cadmium disposition following repeated exposure in the pregnant hamster

Pregnant Syrian hamsters were given a dose of 3.9 micromoles cadmium ion/kg (radiolabelled with 109cadmium) on days 7, 8, 9, and 11 of gestation. Animals were sacrificed on day 13 of gestation and maternal blood, liver, kidney, placentas, and fetuses collected. No pathology was observed in placentas or fetuses. Maternal liver accounted for 61% of the total cadmium injected (15.6 micromoles/kg dam), maternal kidney 4%, and placentas 0.24%. Maternal blood and fetuses contributed negligibly to the total body burden of cadmium. Gel filtration experiments indicated two major cadmium fractions in maternal liver, maternal kidney, and placental cytosols, one at the excluded volume and another nearly twice the excluded volume. Further purification and characterization of the cadmium fraction eluting at twice the excluded volume in the gel filtration experiments showed it to be cadmium metallothionein. Ion exchange chromatography on DEAE Sephacel revealed two forms of cadmium metallothionein in the cytosols of maternal liver and placentas. Maternal kidney cytosols contained one cadmium metallothionein. Amino acid analyses suggest that the thionein components of placental cytosols are synthesized in situ.

Quantitative immunohistochemistry of metallothionein in rat placenta

The presence of metallothionein (MT) was demonstrated in placentae from cadmium-exposed and control rats by an immunohistochemical technique, using peroxidase as label and the diaminobenzidine procedure for the staining reaction. The protein was found in different regions of the placenta, i.e. in trophoblastic labyrinth, in spongiotrophoblast and in visceral yolk sac. Cytophotometric analysis of the final reaction product revealed that the amount of MT was increased in the placental labyrinth of cadmium-exposed rats. Increases were found in both nuclei and cytoplasm of trophoblast cells in the labyrinth region. Possible roles of MT in the transport of zinc and in the carbohydrate metabolism are discussed.

Light and electron microscopic investigation of the rat placenta after cadmium administration during pregnancy

The morphology of the rat placenta was studied after exposure to cadmium chloride during pregnancy, using optimal fixation conditions. In contrast to previous observations, no differences were observed after cadmium administration in relative volume densities of trophoblastic tissue, maternal lacunae, fetal capillaries and connective tissue, nor in trophoblastic thickness or other morphometric features. At the ultrastructural level, the amount of glycogen in trophoblast layer II was elevated in cadmium exposed rats, but other electron microscopic features (amount and localization of lipid, degenerative vesicles, thickness and general appearance of the trophoblastic and endothelial layers and thickening or multiplication of the basal lamina) were not changed. Results obtained from the present experiments do not support the suggestion that cadmium is responsible for structural changes in the placentae of human smokers.

Metallothionein-like proteins in human placenta and fetal membranes

Metallothionein (MT) levels were measured in the term human placenta, chorion, and amnion by the Cd-radioassay method. MT concentrations in the amnion and chorion were 8 to 9 micrograms MT/g tissue while placental levels were approximately half this value. For individual subjects a significant correlation (r2 = 0.96) was found for placental and chorionic MT, while amnionic MT levels did not correlate with either placental or chorionic MT. Gel filtration and uv spectral analysis confirmed the presence of a MT-like protein in cytosol obtained from amnion, chorion, and placenta. MT levels in trophoblasts cultured from chorion were increased upon exposure in vitro to either Cd or Zn.