Chronic cadmium exposure during pregnancy in the mouse: influence of exposure levels on fetal and maternal uptake

Delayed vasculogenesis and impaired angiogenesis due to altered Ang-2 and VE-cadherin levels in the chick embryo model following exposure to cadmium

PURPOSE

Cadmium (Cd) causes chick embryo malformation and abnormal extra-embryonic vasculature. This study investigates the effect of Cd on vasculogenesis, quantifies extra-embryonic vascular development following exposure to cadmium acetate (CdAc).

METHODS

After 48 or 60 h incubation, chicks were explanted and treated with 50 µl of 50 µM CdAc or equimolar sodium acetate. Embryos were again incubated then re-examined 4, 8, 24 and 48 h later. Gross morphological and histological manifestations were noted. Vasculogenesis was assessed by the development of omphalomesenteric vessels from blood islands. Sinus terminalis (ST), area vasculosa (AV), vessel density and embryo crown-rump length (CRL) were measured. Ang-2 and VE-cadherin mRNA expression was analysed by RT-PCR.

RESULTS

Vasculogenesis was delayed on gross and histological examination. ST length, AV area, vessel density and CRL were significantly reduced in the Cd group. Ang-2 was increased 4 h after exposure to Cd, whereas VE-cadherin was reduced.

CONCLUSION

Cd exposure inhibits normal development of extra-embryonic vasculature in line with growth retardation of the chick embryo in association with altered expression of Ang-2 and VE-cadherin.

Mechanisms of cadmium-caused eye hypoplasia and hypopigmentation in zebrafish embryos

Cadmium-caused head and eye hypoplasia and hypopigmentation has been recognized for a long time, but knowledge of the underlying mechanisms is limited. In this study, we found that high mortality occurred in exposed embryos after 24 hpf, when cadmium (Cd) dosage was above 17.8 μM. Using high-throughput in situ hybridization screening, we found that genes labelling the neural crest and its derivative pigment cells exhibited obviously reduced expression in Cd-exposed embryos from 24 hpf, 2 days earlier than head and eye hypoplasia and hypopigmentation occurred. Moreover, based on expression of crestin, a neural crest marker, we found that embryos before the gastrula stage were more sensitive to cadmium toxicity and that damage caused by Cd on embryogenesis was dosage dependent. In addition, by phenotype observation and detection of neural crest and pigment cell markers, we found that BIO and retinoic acid (RA) could neutralize the toxic effects of Cd on zebrafish embryogenesis. In this study, we first determined that Cd blocked the formation of the neural crest and inhibited specification of pigment cells, which might contribute to the molecular mechanisms underlying the phenotype defects of head and eye hypoplasia and hypopigmentation in Cd-exposed embryos. Moreover, we found that compounds BIO or RA could neutralize the toxic effects of Cd.

Toxicological risks for small mammals in a diffusely and moderately polluted floodplain

The ecotoxicological risk of heavy metal pollution in diffusely polluted floodplains is largely unclear, as field-based data are scarce. This study investigated cadmium (Cd) and lead (Pb) accumulation in the liver and kidneys of small mammal species (voles, mice and shrews) from a moderately polluted Dutch floodplain. The Cd and Pb concentrations were compared with effect concentrations (ECs). Reported ECs in literature varied considerably, with the lowest values frequently exceeded by our values, whereas the highest values were encountered only occasionally. Cd and Pb levels were highest in the shrew species, particularly in Sorex araneus. Although toxicological effects at the specimen level were present in these floodplains, effects at population level are thought to be limited, as a result of the animals' relatively short life expectancies (due to recurrent floods) and the rapid maturation of small mammals. Exceptionally high tissue metal concentrations in some specimens of all species indicated local hotspots with peaks in metal concentrations. Sanitizing such local hotspots might reduce toxicological risks.

Influence of cadmium and copper on tissue element levels of pregnant rats

In the current study, we examined the effects of Cd on Cd, Cu, Zn and Fe levels in placenta and maternal and fetal plasma and tissues, the placental weight, total fetal and maternal body weights, and fetal and maternal tissue weights during pregnancy. A total of 21 adult female rats were treated during gestation with drinking water containing one of the following: 70 mg/L of CdCl2, a combination of 70 mg/L of CdCl2 and 70 mg/L of CuSO4, or no addition (control). Placenta Cu and Fe levels, fetal liver and kidney Cu levels, and fetal liver tissue weights were lower in the group administered Cd than in the control group. Also, Cd levels in the placenta, maternal and fetal liver, and maternal kidney were higher in the group treated with Cd than in controls. In the group administered both Cd and Cu, fetal body and tissue weights did not change, but Cd levels in the placenta, maternal and fetal liver, and maternal kidneys were higher than in controls. Zn and Fe levels in the maternal kidney and fetal liver were also lower in this group. Cd exposure during pregnancy resulted in Cd accumulation in maternal and fetal tissues during pregnancy and a decrease in the total weight of fetuses, and the combination of Cd and Cu caused some changes in the both maternal and fetal levels of Cu, Zn, and Fe, but it did not cause changes in the total fetal body weight or the weights of individual tissues.

Effects of perinatal exposure to low-dose cadmium on thyroid hormone-related and sex hormone receptor gene expressions in brain of offspring

Perinatal cadmium (Cd) exposure has been shown to alter behaviors and reduce learning ability of offspring. A few studies have shown that Cd reduced serum thyroid hormones (THs), which are important for brain development during the perinatal period. Brain specific genes, neurogranin (RC3) and myelin basic protein (BMP), are known to be regulated by TH through TH receptors (TR). It has been suggested that RC3 may play roles in memory and learning. In addition, Cd has been suggested to have estrogen-like activity. To evaluate the effects of perinatal low-dose exposure to Cd on thyroid hormone-related gene (RC3, TR-beta1, MBP, RAR-beta) and sex hormone receptor gene (ER-alpha, ER-beta and PgR) expressions in the brain and on behaviors of offspring, mice were administered with 10ppm Cd (from gestational day 1 to postnatal day 10) and/or 0.025% methimazole (MMI; anti-thyroid drug) (from gestational day 12 to postnatal day 10) in drinking water. Also, 0.1% MMI was administered as a positive control (high MMI group). RC3 mRNA expression was reduced in the female brain of combined exposure and high MMI groups and was negatively correlated with the activity in the open-field. ER-alpha, ER-beta and PgR mRNA expressions were decreased in male and female Cd, and female Cd+MMI groups, respectively; among these changes the reduced expression of PgR was opposite to estrogenic action. These results suggested that perinatal exposure to Cd disrupted the gene expressions of sex hormone receptors, which could not be considered to be a result of estrogenic action. Our study indicates that alteration in the gene expressions of RC3 and sex hormone receptors in the brain induced by perinatal Cd and MMI exposure might be one mechanism of developmental toxicity of Cd.

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.

Increased metallothionein in mouse liver, kidneys, and duodenum during lactation

Lactation-induced increases in cadmium absorption and retention have been demonstrated in mid-lactating mice, but no systematic measurements of endogenous metal-binding protein concentrations during lactation have been reported. Using Cd/hemoglobin radioassay, this study detected significant increases in metallothionein (MT) concentrations in liver (4-fold), kidneys (2-fold), and duodenum (2-fold), but not jejunum, of mouse dams on days 13 and 20 of lactation. These increases occurred in the absence of cadmium exposure and were specific to the lactation period; dams 5 days after weaning showed MT levels that were similar to those of nonpregnant (NP) mice. Similarly, Northern blot analyses of livers from lactating mice demonstrated that MT mRNA concentrations in maternal liver during mid-lactation were 6-fold higher than those observed 5 days after pups were weaned. Gel filtration of final supernatants from the Cd/hemoglobin assay confirmed that the Cd-binding molecule induced during lactation was indeed metallothionein. In addition, chromatographic analyses of cytosols from tissues taken from dams administered small amounts of Cd (66 ng/mouse) showed that the trace amounts of Cd absorbed through the maternal gastrointestinal tract during mid-lactation were also bound to the MT. These results indicate MT induction in mouse dams occurs as a physiological consequence of lactation, requiring no external stimulus. This induced MT participates in binding low levels of dietary cadmium consumed by the dam. During lactation, elevated maternal MT may affect pathways for essential trace metals as well as sequester toxic metals harmful to the neonate. Multiparous humans may have increased risk of accumulating environmental Cd.

Teratogenic effects and distribution of cadmium (Cd2+) administered via osmotic minipumps to gravid CF-1 mice

Studies to identify the mechanisms underlying the teratogenic effects of cadmium (Cd2+) have been complicated by the inherent difficulties of chronically and subchronically administering specific doses of Cd2+ to gravid animals under strictly controlled conditions. The objective of the present study was to develop a relatively simple animal model for examining the teratogenic effects of subchronic Cd2+ exposure. Cd2+ was administered to gravid CF-1 mice by subcutaneously implanted Alzet osmotic minipumps, which released fixed amounts of Cd2+ over a 14-day period between days 5 and 18 of gestation. The results showed that Cd2+ administered in this manner produced fetal anomalies and that the patterns of Cd2+ distribution and the specific developmental defects were similar to those that have been reported for other routes of Cd2+ administration. These findings indicate that osmotic minipumps may serve as useful tools in long-term studies of Cd2+ teratogenicity. They would appear to be especially useful in teratogenic evaluations where minimizing maternal stress and administering precise doses of Cd2+ are important.

The ecotoxicological significance of cadmium intake and residues in terrestrial small mammals

Little is known about the ecotoxicological hazard of cadmium to wild small mammals. This paper reviewed laboratory and field studies to determine: (i) intake and residue lowest-observable-adverse-effect-levels (LOAELs) for the ecologically important parameters of reproduction and development; (ii) whether these LOAELs are exceeded by wild small mammals on contaminated habitats and what adverse effects result; and (iii) which species may be at most risk from cadmium. The intake LOAEL in laboratory rodents was 3.5-7.5 mg kg-1 body wt day-1 and the residue LOAEL, based on cellular damage in the kidney, was a renal cadmium concentration of 105 mg kg-1 dry wt. On contaminated habitats, these LOAELs are exceeded by common shrews Sorex araneus but not by wild rodents. However, there is little evidence of adverse cadmium-mediated effects in common shrews and this species may be tolerant to cadmium exposure. Large cadmium concentrations in body organs may simply reflect an ability to store cadmium in a nontoxic, metallothionein-bound state. In contrast, studies suggest that microtine voles may be sensitive to cadmium and, despite their relatively low cadmium intake and accumulated residues, may suffer adverse effects. The need to establish dose-residue-effect relationships for intakes and residues which are appropriate for wild species and also based on ecologically important parameters is discussed.

Cadmium-109 metabolism in mice. IV. Diet versus maternal stores as a source of cadmium transfer to mouse fetuses and pups during gestation and lactation

The transfer of 109Cd from dam to offspring during gestation and lactation was studied in uniparous mice. From 70 to 210 d of age and during the subsequent reproductive period, young adult female mice received drinking water containing tracer amounts of 109Cd (8 ppb total Cd) and nutrient-sufficient or -deficient solid diet containing stable Cd (5 ppm Cd). The nutrient quality of the deficient diet was patterned after that consumed by Japanese women who contracted itai-itai disease. To evaluate established maternal stores as a potential source of cadmium transfer to pups, some dams were switched to water with no 109Cd and diet with an environmental or control level of cadmium (0.25 ppm Cd) during the reproductive period. The resulting pups were analyzed for 109Cd at birth and at 7-d intervals throughout the lactation period. Pup 109Cd content at birth, representative of the amount transferred via the placenta during gestation, accounted for less than 1% of the total 109Cd transferred during the full reproductive period. During lactation, 109Cd levels in pups from dams with current 109Cd exposure approximately tripled with each 7-d interval; no significant differences occurred due to nutrient quality of the dams' diet. For 21-d-old pups, 98% of the 109Cd burden came from the diet of the dam, while only 2% came from her tissue stores, primarily the hepatic one. Such fractions represented a transfer per pup of about 0.01% of the oral 109Cd dose ingested by the dam during the reproductive period and about 0.05% of the 109Cd in her tissue stores. Overall, transfer per litter amounted to about 7% of the dietary 109Cd dose absorbed and retained by the dam during that interval and about 0.2% of the 109Cd from tissue stores. On lactation d 21, 90% of the total 109Cd in pups was sequestered in the gastrointestinal tract. Cadmium transfer was additionally examined in multiparous mice that began a repetitive breeding program at 70 d of age at the time of introduction to the same diet/water regimens already described. Overall, females consuming nutrient-sufficient diet experienced 5 consecutive 42-d rounds of gestation/lactation, while their deficient diet counterparts experienced 3 nonconsecutive rounds during an equivalent period. Transfer was examined during their last gestation/lactation experience. Throughout the lactation interval, 109Cd transfer to pups was about 30% increased for multiparous versus uniparous females; however, transfer again was not significantly affected by nutrient quality of the dams' diet.(ABSTRACT TRUNCATED AT 400 WORDS)

Cadmium-109 metabolism in mice. III. Organ retention in mice ovariectomized after experiencing multiple rounds of gestation and lactation

Organ retention of 109Cd was studied in multiparous female mice 6 wk after ovariectomy or sham-control surgery. Females previously had experienced from three to five rounds of gestation/lactation during a maximum of 5 successive, 42-d reproductive periods. Throughout the experiment, mice were provided with tracer amounts of 109Cd in drinking water as well as stable Cd appropriate for the itai-itai experience in solid diets otherwise sufficient or deficient in nutrient quality. For sufficient-diet females, organ 109Cd content and concentration values were somewhat lower in the ovariectomized group compared to the sham control group. For deficient-diet females, the opposite trend occurred. When ovariectomized groups were compared with round 5 breeder groups of the same dietary experience, in almost all instances organ 109Cd content and concentration values were lower in the ovariectomized animals. Exceptions to this trend occurred in hepatic and especially renal tissues, where 109Cd concentrations were higher in the deficient-diet, ovariectomized group. Finally, when the deficient-diet, ovariectomized group was compared with its sufficient-diet counterpart, significantly higher 109Cd content values were found for liver, kidneys, and whole body (minus GI tract) in the former group. Conversely, when the same tissue content values were compared between the sham-control groups, differences without exception proved to be nonsignificant.

Cadmium toxicity in perinatal rat hepatocytes: electron microscopy, X-ray microanalysis, and morphometric analysis

Effects of cadmium on the fetal and postnatal rat hepatocytes were studied with an electron microscope and an X-ray microanalyzer. Pregnant and lactating Wistar rat dams at 15 and 21 days of pregnancy and at 3 days after delivery received intraperitoneal injections of cadmium sulfate (1 mg/kg body weight) for 3 days. On the day following the last injection, the livers were isolated from the fetal and suckling rats and provided for electron microscopy. The livers from the untreated fetal and newborn rats served as control. Large bile canaliculi, which were formed by five or more hepatocytes, were frequently observed in the cadmium-treated perinatal rat livers. The intercellular space between each adjacent hepatocyte was widened. By X-ray microanalysis, cadmium peaks were preferentially detected out from intramitochondrial granules of the cadmium-treated hepatocytes. By morphometric analysis, the increase both in the mitochondria volume and in the number of intramitochondrial granules was evident in the cadmium-treated hepatocytes when compared to those of control. These data suggest the preferential accumulation of cadmium in mitochondria of the hepatocytes interferes with the morphogenesis of the perinatal rat liver.

Placental transfer of metals of coal fly ash into various fetal organs of rat

Fly ash (100 mg/kg body weight) was administered intratracheally to 14-day pregnant rats for 6 consecutive days. On day 20 of gestation the translocation of metals present in the fly ash to various maternal and fetal organs was studied. Fly ash administration to pregnant mothers retarded the growth of fetal heart and kidney as determined by their weights. Fly ash instillation increased organ levels of nearly all the metals studied in both mother and fetus. Most of the metals present in coal fly ash were transferred in significant amounts through placenta to several fetal organs. However, the pattern of their distribution into various fetal organs was different for different metals.