Tangshen Formula Ameliorates Diabetic Nephropathy by Suppressing Soluble Epoxide Hydrolase Activity to Enhance IRS2-Mediated PI3K/AKT Signaling

Background: Diabetic nephropathy (DN), a leading cause of end-stage renal disease, demands novel therapeutic strategies. This study investigated the ability of Tangshen formula (TSF) to modulate DN via a renoprotective mechanism involving soluble epoxide hydrolase (sEH) - and insulin receptor substrate 2 (IRS2) - dependent phosphatidylinositol-3 kinase (PI3K)/AKT (protein kinase B) - eNOS (endothelial nitric oxide synthase) signaling. Methods: A diabetic rat model with hypermethioninemia was established by administering two intraperitoneal injections of streptozotocin (STZ; 30 mg/kg) and feeding a 2% hypermethioninemia (HM) diet. Rats were divided into normal, STZ, HM+STZ, and TSF (3.6 g/kg/day) groups ( n = 8 each) and treated for 12 weeks. Renal expression of sEH, IRS2, PI3K, AKT, and eNOS was evaluated using quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR), western blot, and immunohistochemistry. Results: Diabetic rats showed a 1.4-2.0-fold increase in sEH mRNA and an 11.3-19.6-fold rise in sEH protein levels, accompanied by an 82%-83% reduction in IRS2 mRNA, a marked decrease in IRS2 phosphorylation (15%-16% of normal), and significant impairment of PI3K/AKT-eNOS signaling. TSF treatment reduced sEH mRNA expression by 30% and protein levels normalized, restored IRS2 expression to 61% of the control value, and improved phosphorylation of PI3K, AKT, and eNOS. Conclusion: TSF confers renoprotection in DN by suppressing sEH overexpression and by reactivating the IRS2-mediated PI3K/AKT-eNOS pathway. TSF has potential as a multi-target therapeutic agent for diabetic microvascular complications.