RESUMO
Teratogenicity of the anticonvulsant phenytoin may be due in part to its bioactivation by prostaglandin synthetase, forming a reactive free radical intermediate. We examined whether teratogenicity of the structurally similar oxazolidinedione anticonvulsants, trimethadione and its N-demethylated metabolite dimethadione, could be inhibited by the prostaglandin synthetase inhibitor acetylsalicylic acid (ASA). Trimethadione, 700 or 1000 mg/kg intraperitoneally (ip), was given to pregnant CD-1 mice during (Gestational Days 12 and 13) or before (Days 11 and 12) the critical period of susceptibility to phenytoin-induced fetal cleft palates. Dimethadione was given similarly on Days 11 and 12, or 12 and 13, in a dose (900 mg/kg ip) that was equimolar to 1000 mg/kg of trimethadione. ASA, 10 or 1 mg/kg ip, was given 2 hr before trimethadione or dimethadione on Days 11 and 12, and before trimethadione on Day 11 only. Dams were killed on Day 19 and fetuses were examined for anomalies. Either dose of trimethadione given on Days 12 and 13 was negligibly teratogenic, as evidenced by a non-dose-related, 1.1% mean incidence of fetal cleft palates. However, when given earlier on Days 11 and 12, trimethadione 1000 mg/kg caused an 8.9% incidence of cleft palates (p less than 0.05). Similarly, dimethadione caused a 3.9-fold higher incidence of cleft palates when given earlier on Days 11 and 12 (17.3-34.9%) than on Days 12 and 13 (4.4%) (p less than 0.05). At equimolar doses, dimethadione caused a 1.9- to 3.9-fold higher incidence of cleft palates compared to trimethadione (p less than 0.05), suggesting that dimethadione may be the proximate teratogen. Either dose of ASA given on both days before trimethadione totally prevented cleft palates, and ASA 10 mg/kg given only on Day 11 reduced the incidence of trimethadione-induced cleft palates to 1.1% (p less than 0.05). ASA reduced the incidence of cleft palates caused by dimethadione given on Days 11 and 12 from 34.9 to 20.3% (p less than 0.05). These results suggest that the teratogenic potential of trimethadione may depend at least in part upon its prior N-demethylation to dimethadione, which then can be bioactivated by prostaglandin synthetase to a teratogenic reactive intermediate, possibly involving a free radical located in the oxazolidinedione ring. This would provide a unifying hypothesis for the teratogenicity of hydantoins, as well as structurally related teratogens like trimethadione, which lack the molecular configuration necessary for the formation of a teratogenic arene oxide intermediate.
