Embryotoxicity and Teratogenicity of Streptozotocin-Induced Insulin-Deficient Maternal Diabetes in Sprague-Dawley Rats: A Comparative Evaluation of Insulin Glargine, Metformin, and Combined Therapy

Background & Objective: Pregestational diabetes is a leading preventable cause of congenital anomalies. We characterized Streptozotocin (STZ)-induced insulin-deficient diabetic embryopathy and compared the effects of insulin glargine, metformin, and their combination.Materials & Methods: Forty-eight time-mated Sprague-Dawley dams were allocated by blinded block randomization into six groups (n=8 litters per group): normal control, citrate-buffer vehicle control, STZ-induced diabetic, and STZ-diabetic treated with insulin glargine (2 IU/kg/day s.c.), metformin (200 mg/kg/day p.o.), or their combination from Gestational Day (GD) 8 to 20. Diabetes was induced via STZ (50 mg/kg i.p.) on GD 7. Fetuses were harvested on GD 20-21 for morphometric, histopathological, biochemical, and molecular analyses, with a satellite cohort providing GD 12-18 data.Results: Diabetic dams developed hyperglycemia (389.2±22.6 mg/dL at GD 20), a fetal malformation prevalence of 44.3% (95% CI 38.1-50.7), and a fourfold increase in placental malondialdehyde levels. Pax3 and Sox2 transcripts decreased to 31% and 28% of control values, respectively, while cleaved Caspase-3 levels increased 4.82-fold. Combined therapy provided the greatest protection, restoring fetal weight to 91.2% of control and reducing malformation prevalence to 4.7% (95% CI 2.4-8.6), significantly outperforming insulin monotherapy in reducing malformations and modulating Pax3, Nrf2, and Caspase-3 levels.Conclusion: This model produced reproducible embryopathy associated with placental oxidative stress, neuroepithelial apoptosis, and transcriptional dysregulation of morphogenesis. Combined therapy provided superior restoration compared with either monotherapy, supporting complementary glycemic and non-glycemic mechanisms; however, further confirmation is warranted before clinical extrapolation.