Cadmium exposure on day 12 of gestation in the Wistar rat: distribution, uteroplacental blood flow, and fetal viability

Effects of cadmium on the expression of placental lactogens and Pit-1 genes in the rat placental trophoblast cells

Cadmium is an endocrine disrupter (ED) with detrimental effects on mammalian reproduction. The placenta is a primary target for cadmium toxicity during pregnancy. Very little of this metal crosses the placenta to the fetus, and consequently it accumulates in high concentrations in the placenta. Cadmium affects on steroid synthesis and has estrogen- and androgen-like activities. In this study, we investigated the toxic effects of cadmium on placental trophoblast cells as well as the mRNA levels of placental lactogens (PLs), which are under the control of estrogen and play a pivotal role during pregnancy. Pregnant F344 Fisher rats were injected subcutaneously with 0, 0.2, and 2.0mg/kg BW/day of cadmium (CdCl(2)) dissolved in saline from days 11 to 19 of pregnancy and were sacrificed on day 20. The mRNA levels of the PL-Iv and -II genes and Pit-1alpha and beta isotype genes, the trans-acting factor of PLs, were analyzed by Northern blot hybridization and reverse transcription-polymerase chain reaction, respectively. The frequency of the placental trophoblast cells was observed histochemically. Developmental data and apoptotic chromosomal DNA fragmentation of placental cells were also observed. The mRNA levels of PL-Iv and -II were reduced in a dose-dependent manner by cadmium. The mRNA levels of the Pit-1alpha and beta isotype genes were also reduced by cadmium. In the uterus-conjugated region of the placental junctional zone, the frequency rates of trophoblast cells were lower in the cadmium-treated groups than in the control group. High-dose cadmium exposure (2.0mg) induced not only the reduction of trophoblast cell frequency but also apoptotic chromosomal DNA fragmentation in the junctional zone of the placenta. Developmental metrics such as placental and fetal weights and a number of live fetuses, decreased, while a numbers of resorptions, dead fetuses, and post-implantation losses increased significantly (p<0.05) in the cadmium-treated groups compared to the control. These data suggested that cadmium inhibits the expression of PL genes and reduces the number of trophoblast cells in the rat placenta via an estrogen-like activity, leading to significant toxic effects on placental growth and physiological function in rats.

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.

An introduction to reactive oxygen species and their possible roles in substance abuse

There is a growing body of information relating diverse diseases and the consequences of injury to generation and toxicity of reactive oxygen species (ROS). Recently, it has been shown that the fetus and its membranes are also vulnerable to this toxicity, suggesting that a number of obstetric diseases may result from exposure to ROS, which are ubiquitous in aerobic organisms. Endogenous antioxidants, including superoxide dismutase, catalase, and glutathione peroxidase are essential for defense against ROS. It is significant that all antioxidants appear to be down-regulated in the fetus and membranes, suggesting the possibility that any process that further depresses their activities or increases the burden of ROS may compromise fetal development or maternal health. When permitted to accumulate, ROS can damage all classes of macromolecules, including lipids, proteins, and nucleic acids. Toxicity includes mutation, protein degradation, and lipid peroxidation, which can severely disturb membrane permeability and alter intracellular calcium and pH. An understanding of the generation and toxicity of ROS should help to define their potential roles in obstetric disease and lead to innovative preventive and therapeutic approaches.

Energy charge monitoring via magnetic resonance spectroscopy 31P in the perfused human placenta: effects of cadmium, dinitrophenol and iodoacetate

Phosphorus 31 nuclear magnetic resonance spectroscopy as a non-invasive technique was applied to monitor the metabolic activity of the human placenta during perfusion in vitro. During control perfusions (n = 3) there was an initial increase in adenosine triphosphate (ATP) and a fall in inorganic phosphate (Pi). Thereafter, however, the level of both ATP and Pi remained constant throughout the perfusion period (11 h). Additional biochemical parameters such as glucose consumption, lactate production and the release of hormones, human chorionic gonadotrophin (hGC). measured in the perfusate samples, were also used to assess the viability of the placental tissue. As with ATP, all these biochemical parameters under the control conditions showed a stable rate of metabolic activity throughout the length of the experiments. In additional experiments, the effect of the metabolic inhibitor dinitrophenol (n = 2) and dinitrophenol (DNP) together with iodoacetic acid (IOA, n = 2) were studied. DNP (0.1 mM) alone showed a slight decrease of all parameters. In contrast, the addition of IOA (0.1 mM) with DNP (0.1 mM) not only blocked the production of ATP but also produced a substantial impact on placental metabolic activity. The effect of a toxic dose of cadmium (20 nmol/ml) was studied also (n = 3). This dose of cadmium demonstrated no effect on phosphorus metabolism. However, the rate of glucose consumption and the release of hCG were significantly reduced.

The placental transfer and toxicity of selenite relative to cadmium in the human term perfused placenta

Selenite and cadmium both cause reproductive effects in animals. Cadmium is an acute placental toxicant, with apparent limited transfer to the fetus. This study examines the placental transfer of selenite, and the hypothesis that similar to cadmium, selenite may also be a direct placental toxicant. Using dual perfusion of the human term placental lobule, both non-protein bound (< 776 Da) selenite and cadmium equilibrated across the placenta within 4 h. The transfer of selenium, added as selenite, was not limited at concentrations from 2-40 nmol/ml. At initial maternal concentrations of 20 nmol/ml, selenium attained higher concentrations in the fetal perfusate compared with cadmium concentrations. Protein binding of cadmium in perfusates (45 per cent at 30 min) and placental cytosol (approx. 87 per cent) was greater than selenium (perfusate, 7 per cent at 30 min, cytosol, 50-60 per cent), which may partially account for the differences in placental transfer. Cadmium (20 nmol/ml) produced adverse effects on the production and release of human chorionic gonadotropin (hCG) in 4 h. No adverse effects were noted during 4 h exposures to selenite at initial concentrations of up to 40 nmol/ml. Thus, unlike cadmium, in which placental accumulation and direct placental toxicity contributed to acute reproductive effects, selenite at concentrations up to 40 nmol/ml was not a direct toxicant under these perfusion conditions.