Significance of glutathione-dependent antioxidant system in diabetes-induced embryonic malformations

Hyperglycemia-induced embryonic malformations may be due to an increase in radical formation and depletion of intracellular glutathione (GSH) in embry onic tissues. In the past, we have investigated the role of the glutathione -dependent antioxidant system and GSH on diabetes-related embryonic malform ations. Embryos hom streptozotocin-induced diabetic rats on gestational day 11 showed a significantly higher frequency of embryonic malformations (neu ral lesions 21.5 vs. 2.8%,P < 0.001; nonneural lesions 47.4 vs. 6.4%, P < 0 .001) and growth retardation than those of normal mothers. The formation of intracellular reactive oxygen species (ROS), estimated by flow cytometry, was increased in isolated embryonic cells of diabetic rats on gestational d ay 11. The concentration of intracellular GSH in embryonic tissues of diabe tic pregnant rats on day 11 was significantly lower than that of nor mal ra ts. The activity of gamma-glutamylcysteine synthetase (gamma-GCS), the rate -limiting GSH synthesizing enzyme, in embryos of diabetic rats was signific antly low associated with reduced expression of gamma-GCS mRNA. Administrat ion of buthionine sulfoxamine (BSO), a specific inhibitor of gamma-GCS, to diabetic rats during the period of maximal teratogenic susceptibility (days 6-11 of gestation) reduced GSH by 46.7% and increased the frequency of neu ral lesions (62.1 vs. 21.5%, P < 0.01) and nonneural lesions (79.3 vs. 47.4 %, P < 0.01). Administration of GSH ester to diabetic rats restored GSH con centration in the embryos and reduced the formation of ROS, leading to norm alization of neural lesions (1.9 vs. 21.5%) and improvement in nonneural le sions (26.7 vs. 47.4%) and growth retardation. Administration of insulin in another group of pregnant rats during the same period resulted in complete normalization of neural lesions (4.3 vs. 21.5%), nonneural lesions (4.3 vs . 47.4%), and growth retardation with the restoration of GSH contents. Our results indicate that GSH depletion and impaired responsiveness of GSH-synt hesizing enzyme to oxidative stress during organogenesis may have important roles in the development of embryonic malformations in diabetes.