H. Sakamaki et al., Significance of glutathione-dependent antioxidant system in diabetes-induced embryonic malformations, DIABETES, 48(5), 1999, pp. 1138-1144
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.