Teratogenesis induced by short and long‐term exposure ofxenopus laevisprogeny to lead

Abstract

Short-term (96-h) tests on Xenopus laevis embryos are advocated for rapid screening of teratogens, as an alternative to the use of mammals. The objective of the present investigation was to determine whether extending the short-term tests beyond 96 h would detect the teratogenicity of chemicals that would otherwise be missed by the short-term tests. Lead teratogenicity was examined in Xenopus, using lead concentrations of 0.02, 0.05, 0.1, 0.5, 1.0, and 3.0 mg/L, which bracket the U.S. Environmental Protection Agency (EPA) maximum allowable concentration of 0.05 mg/L in water. Short-term exposure times were 72 or 96 h, starting on d 1, 2, or 3 postfertilization, while long-term exposure covered d 1 through metamorphosis. Short-term exposure resulted in neural tube defects (when exposure included d 1 and/or d 2) and tail curvatures, but only at the higher lead concentrations (1 and 3 mg/L). Lower lead concentrations produced no malformations upon short-term exposure, and this corresponded with the absence of tissue lead uptake. On the other hand, long-term exposure to lead (> 3 wk) resulted in the delayed appearance of lordoscoliosis at low lead concentrations (0.02-0.1 mg/L). The delayed appearance of lordoscoliosis corresponded roughly with the attainment of stable lead tissue levels, and this malformation persisted after metamorphosis. Thus, short-term observation tests alone may fail to detect the teratogenicity of low concentrations of environmental chemicals, and may result in the setting of inappropriately liberal exposure standards.

Assessment of Lead Ecotoxicity in Water using the Amphibian Larvae (Xenopus laevis) and Preliminary Study of its Immobilization in Meat and Bone Meal Combustion Residues

“…Chemical analysis performed on the positive control group of experiment A (which had no identified source of lead), showed that low contamination did occur during the exposure. Other, similar findings have been reported in whole body of control animals Sobotka & Rahwan 1995). In our case, minimal contamination could come from the tap water, the diet source or from the CP added which might not have been completely exempt of metal traces.…”

“…For instance, in Bufo arenarum, lead induces deformities such as underdeveloped gills, sigmoidal body shape, and stunted tails at various stages of development (Pe´rez-Coll et al 1988;Pe´rez-Coll & Herkovits 1990); in Xenopus laevis, it induces neural tube defects, tail curvature and lordoscoliosis (Sobotka & Rahwan 1995). The recent paper of Fink and Saliban (2005) summarizes the results of studies that examined the biochemical and physiological effects of Pb in an in vivo amphibian model (B. arenarum).…”

“…The toxicological effects of lead are extensively documented in many physiological systems notably in man (Ter Haar 1981;Kopp et al 1988;Landrigan 1990;Verity 1990;Beck, 1992;Goyer 1993;Papanikolaou et al 2005) but amphibians have also been particularly well investigated (Perez-Coll et al 1988;Pe´rez-Coll & Herkovits 1990;Steele et al 1991;Sobotka & Rahwan 1995;Stansley & Roscoe 1996;Stansley et al 1997;Kumar 1999;Rice et al 2001;Rosenberg et al 2003;Fink & Salibian 2005). However, the vast majority of the studies devoted to the impact of lead in amphibians have been oriented towards toxicity, physiology, biochemistry and immunology in embryos or adults and very little or no information is currently available on the genotoxic effects of lead, especially in larvae.…”

“…A variety of strategies has been employed to determine the effect of environmental pollutants on amphibians: organisms placed in the field (Cooke 1981), organisms exposed in the lab to media harvested from field sites (Burkhart et al 1998;Gauthier et al 2004;Mouchet et al 2005aMouchet et al , b, 2006 or organisms exposed in the lab to controlled laboratory conditions (Pe´rez-Coll & Herkovits 1990;Sobotka & Rahwan 1995;Mouchet et al 2005b). In the present investigation, amphibian larvae were exposed to lead in controlled lab conditions in order to evaluate three different endpoints after 12 days of exposure according to the French standard micronucleus assay (AFNOR 2000): (i) acute toxicity of larvae (ii) genotoxicity as the expression of the clastogenic and/or aneugenic effects of lead in the erythrocytes of the circulating blood (iii) and Pb accumulation in the liver.…”

Sublethal effects of lead on northern leopard frog (Rana pipiens) tadpoles

“…For example, Perez‐Coll et al [6] found that toad ( Bufo arenarum ) embryos exposed to Pb experienced arrested development, underdeveloped gills, curved tails, and increased mortality. Sobotka and Rahwan [7] showed that Pb exposure resulted in neural tube defects and spinal deformities in Xenopus laevis tadpoles. Other researchers found more subtle effects, including inhibited learning performances and hypoxia‐like responses in bullfrog ( Rana catesbeiana ) tadpoles exposed to Pb [8].…”