1,25-D3 Protects Diabetic Brain Injury Through GLP-1R/PI3K/Akt Pathway by Experimental and Molecular Docking Studies

Background: Diabetes can cause an increase in intracellular glucose, leading to neuronal damage and microvascular dysfunction. Neuroprotective agents 1α,25-dihydroxyvitamin D3 (1,25-D3) can reduce neurological complications. The main purpose of this study is to evaluate the levels of inflammatory factors and vascular protective factors in streptozotocin (STZ)-induced diabetic rats and determine whether 1,25-D3 can protect the rat brains from hyperglycemia through the glucagon-like peptide-1 (GLP-1)R/PI3K/AKT signal pathway. Methods: We first evaluated whether the relevant target could effectively bind to 1,25-D3 through molecular docking. Next, we established STZ-induced diabetic rat models for in vivo experiments to verify the targets in molecular docking that have good binding effects on 1,25-D3. After 8 weeks of a high-fat diet (HFD) and an intraperitoneal injection of STZ (35 mg/kg body weight), the experimental type 2 diabetic rat model was created, and the morphological changes of the cerebral cortex were measured by performing hematoxylin and eosin (H&E) staining. Western blotting (WB) was used to detect the proteins' expression of relevant targets, and the RT-qPCR was used to analyze the mRNA levels of relevant targets in the cerebral cortex. We also utilized the enzyme-linked immunosorbent assay (ELISA) kit for detecting the protein content of relevant targets. Results: Molecular docking showed that 1,25-D3 had good binding ability with related targets, such as GLP-1R, PI3K, AKT1, vascular endothelial growth factor-α (VEGF-α), endothelial nitric oxide (NO) synthase (e-NOS), intercellular adhesion molecule-1 (ICAM-1), and vascular intercellular adhesion molecule-1 (VCAM-1). Experimental verification results found that 1,25-D3 partially prevented abnormalities in brain function and structure caused by diabetes. Meanwhile, the ICAM-1 and VCAM-1 levels were increased in the high-glucose group, e-NOS levels were decreased, and the relative expression of GLP-1R, VEGF-α, p-PI3K/PI3K, and p-AKT/AKT was reduced. 1,25-D3 abolished these changes, and these effects were suppressed by specific inhibitors. Conclusions: 1,25-D3 alleviates neuroinflammation and improves vascular endothelial dysfunction through multitarget and multipathway by upregulating the GLP-1R/PI3K/AKT signaling axis to improve diabetes-induced brain injury.