Evaluating the Prophylactic and Nephroprotective Effects of Vitamin D and Metformin in Diabetic Nephropathy

Introduction: Diabetic nephropathy (DN), a major complication of diabetes mellitus (DM) and a leading cause of end-stage renal disease (ESRD) globally, is characterized by oxidative stress (OS), chronic inflammation, and progressive fibrosis. Despite existing treatment options, disease progression remains a challenge. This study evaluates the therapeutic potential of vitamin D, alone and in combination with metformin, in mitigating DN progression in streptozotocin (STZ) induced diabetic rats. Methods: Male Wister rats were induced with diabetes using a single intraperitoneal injection of STZ and randomized into seven groups. Treatment regimens included vitamin D (5000 or 8000 IU), metformin (250 mg), or a combination, administered over 12 or 21 weeks. Fasting blood glucose (FBG), lipid profiles, renal function markers, and OS indicators were assessed. Renal tissues were examined via histopathological analysis to assess structural changes, and immunohistochemistry (IHC) was performed to evaluate the expression of key proteins involved in inflammation (transforming growth factor-beta [TGF-β]), fibrosis (VEGF), and OS (nuclear factor erythroid 2-related factor 2 [Nrf2]), and vitamin D receptor (VDR) signaling. Results: Vitamin D treatment caused a dose-dependent decrease in FBG, with the vitamin D and metformin combination therapy achieving the greatest decrease (-49.8%) by week 21. Triglyceride levels were significantly reduced (-50%), while HDL levels remained stable. Combination therapy significantly reduced hydrogen peroxide (H₂O₂) (-36.84%) and nitric oxide (NO) (-14.29%) and enhanced antioxidant enzyme activity: glutathione reductase (GR) (+250%), Superoxide dismutase (SOD) (+11.33%), and Glutathione peroxidase (GPx) (+62.83%). Histological analysis revealed preserved renal architecture and reduced fibrosis in treated groups, particularly in those receiving combination therapy. IHC showed increased VDR and Nrf2 expression, reduced VEGF and TGF-β levels, reflecting attenuation of inflammation, fibrosis, and oxidative damage. Conclusion: Vitamin D, particularly in combination with metformin, significantly attenuates DN progression by enhancing metabolic control, reducing OS, and preserving renal function. These findings support its potential as an effective adjunctive therapy in DN management and provide a foundation for future clinical investigations.