Cytotoxic effects of ethylene glycol monomethyl ether in the forelimb bud of the mouse embryo

The role of cytotoxicity in digital maldevelopment in CD-1 mouse embryos was examined following dosage with ethylene glycol monomethyl ether (EGME) on gestation day (gd) 11. Patterns of cell necrosis in the forelimb buds of embryos collected from dams given EGME orally at doses of 100, 250 or 350 mg/kg were characterized by staining with Nile blue A. Cell death was induced in the mesenchymal tissue and to some extent in the limb bud ectoderm, including the apical ectodermal ridge in a dose-related manner. The area of preaxial physiological cell necrosis was enlarged by EGME, and the shape of the limb buds was altered 24 hr after treatment. Preaxial tissue and the predigital chondrocyte condensations were reduced or missing following 250 and 350 mg EGME per 1 kg. Light and electron microscope evaluations of forelimb buds revealed the presence of phagocytic vacuoles and condensed, fragmented cytoplasm, which indicate cytotoxicity, as early as 2 hr following EGME, a maximum effect being observed 6 hr after the dose was administered. Although the severity of the cytotoxic response appeared to be dose-related, comparison with the incidence of digital malformations in near-term fetuses indicates that the loss of mesenchymal tissue is partially compensated for as formation of the limb progresses.