Comparative Study of Phellodendron amurense Rupr. Components in Alleviating Diabetic Kidney Disease via the PI3K/AKT/GSK-3β/Nrf2 Pathway

Background: To investigate the protective effects of Phellodendron amurense Rupr. polysaccharides (PAP), alkaloids, and flavonoids in alleviating diabetic kidney disease (DKD) and to elucidate the role of the PI3K/AKT/GSK-3β/Nrf2 signaling pathway. Methods: Active components were extracted and quantified. In vitro, high-glucose (HG)-induced human kidney-2 (HK-2) cells were used to screen the optimal fraction via CCK-8, reactive oxygen species (ROS), TdT-mediated dUTP Nick-End Labeling (TUNEL), and Western Blot (WB) assays. In vivo, a DKD rat model was established using 2% Streptozotocin (STZ) and a high-fat with high-sugar diet. Rats were treated with PAP and LY294002. Renal damage and signaling pathway proteins were evaluated using histological staining and WB. Results: Among the tested components, PAP conferred the most pronounced cytoprotection against HG-induced injury in HK-2 cells. PAP significantly reduced glomerular damage, collagen deposition, and glycogen accumulation in the kidneys of DKD rats. Mechanistically, PAP activated the PI3K/AKT/GSK-3β/Nrf2 pathway, upregulating HO-1 and NQO1, while inhibiting the TGF-β1/Smad2 pathway and Bcl-2/Bax-mediated apoptosis. These protective effects were significantly attenuated by LY294002. Conclusions: Among the tested fractions under the present experimental conditions, PAP exhibited the most pronounced protective activity. These protective effects were partially mediated through the PI3K/AKT/GSK-3β/Nrf2 pathway, which enhanced antioxidant capacity while reducing fibrosis and apoptosis.