In Vitro Developmental Toxicity of Aspirin and Its Major Metabolites on Cultured Fetal Mouse Palates

Palatal primordia of day-12.5 ICR mouse fetuses were cultured in a chemically-defined serumless medium by a suspension culture technique, and the developmental toxicity of aspirin and its metabolites on in vitro palatogenesis was studied. Explanted fetal palates were exposed in vitro for 72 hr to 0.5-2 mM aspirin (ASP), 0.25-2 mM salicylic acid (SA), 0.5-2 mM salicyluric acid (SUA), 1–2 mM 2,3-dihydroxybenzoic acid (3DHB), or 1–2 mM 2,5-dihydroxybenzoic acid (5DHB). After 72 hr culture, ASP at 2 mM and SA at 0.25 mM inhibited the growth and fusion of palatal shelves, and SUA at 1 mM prevented palatal fusion. On the other hand, 3DHB and 5DHB did not exert any significant toxic effects on cultured palates at concentrations up to 2 mM. Judging from the 50% inhibitory concentration (IC50), SA (IC50= 0.9 mM) was the most toxic of the 5 compounds tested, with a decreasing order of ASP (IC50= 1.5 mM), SUA (IC50= 1.6 mM), and DHBs (IC50= over 2 mM for both 3DHB and 5DHB). With respect to developmental toxicity, cultured fetal mouse palates showed the susceptibility to aspirin and its metabolites which is intermediate between the susceptibility of rat embryos in vivo and that of postimplantation rat embryos cultured in vitro. The significance of fetal organ culture for evaluating developmental toxicity of chemicals is also discussed.