Maternal exposure to Cd(II) causes malformations of Xenopus laevis embryos

The FETAX (Frog Embryo Teratogenesis Assay: Xenopus) protocol was adapted to determine whether or not exposure of mature female Xenopus to CdCl2 causes malformed embryos. Twelve females (Group A) were exposed to 18 microM Cd(II) for 11 wk; eight females (Group B) were exposed to 90 microM Cd(II) for 4 wk; controls were also tested. The females were induced to ovulate; their eggs were fertilized with sperm from unexposed males; the embryos were scored for malformations at 101 h post-fertilization, and some were analyzed for Cd and metallothionein. The incidence of malformations was increased in embryos from Group A (median 14 percent, p < 0.05 vs 6 percent in controls), but not from Group B (7 percent). At the blastula stage, Cd content averaged 7.0 (SD +/- 2.8) pmol/embryo (Group A), 6.0 +/- 2.6 (Group B), and < 0.2 (controls); the Cd content was correlated with the malformation incidence in progeny of Group A. At the blastula stage, metallothionein averaged 8.1 +/- 2.9 pmol/embryo (Group A), 8.4 +/- 2.5 (Group B), and 6.3 +/- 1.7 (controls, p < 0.05 vs A or B). This study shows that prolonged maternal exposure to Cd(II) can induce malformations in Xenopus embryos. This study also shows that cadmium is transferred from dam to embryo, probably by Cd(II)-binding to yolk proteins and metallothionein, and suggests that Cd(II)-induced embryotoxicity is influenced by the timing of Cd(II) exposure during oogenesis.