The effect of methylmercury exposure on early central nervous system development in the zebrafish (Danio rerio) embryo.
Although much attention has focused on environmental contamination by heavy metals, pesticides, and polychlorinated biphenyls, potential deleterious effects of naturally occurring organic compounds have received much less consideration. Saponins, which are glycosides found in many plants, are important, environmentally ubiquitous organic compounds. Saponins have both beneficial and deleterious effects in adults, but little is known about how saponins effect early vertebrate embryonic development. The authors tested the toxicity of quillaja saponin using a zebrafish embryo assay. Quillaja saponin, extracted from bark of the tree, Quillaja saponaria, is a common foaming agent used in foods and beverages. At 6 h post fertilization, zebrafish embryos were exposed to five concentrations (0 [negative control], 1, 5, 10 or 20 micro g) of quillaja saponin per milliliter of medium. Zebrafish embryos exposed to 2% ethanol were positive controls (100% embryonic death). Embryos were assessed at 30, 54, and 72 h post fertilization for changes in embryonic development, mortality, time of hatching, and morphological deformities. Embryos exposed to 1 and 5 micro g saponin were healthy, showed no obvious deformities, but exhibited shrinkage of the chorion. Hatching time for zebrafish embryos exposed to 1 and 5 micro g/ml saponin decreased by 18 h compared to unexposed embryos. Zebrafish embryos treated with 5 micro g/ml saponin responded less to touch than embryos treated with 1 micro g/ml saponin or controls. Zebrafish embryos exposed to more than 5 micro g/ml saponin exhibited 100% embryonic mortality. These results indicate that exposure to 5 micro g/ml or less of quillaja saponin acts as a growth promoter, whereas concentrations of 10 micro g/ml or greater are lethal.