Procyanidin B2 improves insulin resistance by regulating the IRS1/PI3K/AKT-Nrf2-GSK3β based on computational biology, molecular evidence and direct binding proof

Procyanidin B2 (PB2), a dimer of oligomeric procyanidins, has been reported to ameliorate abnormal glucose metabolism; however, its efficacy in regulating redox-related insulin resistance (IR) and underlying mechanism has not yet been studied. Currently, antioxidant activity and digestive enzyme inhibitory tests were applied to screen the preliminary chemopreventive effect of PB2 on glucose metabolism dysfunction, further computational biology and molecular verification to elucidate its mechanism on improving IR. The results indicated that PB2 had limited antioxidant property against ROS and inhibitory property on digestive enzyme. Network pharmacology analysis implied that PI3K/AKT and FoxO pathways were the main targeted by PB2 to combating IR. Further molecular data demonstrated that PB2 promoted glycogen synthesis by activation of PI3K/AKT-Nrf2 signaling pathway via promoting posttranscriptional protein stability, nuclear translocation of Nrf2 and ARE binding ability, and inhibited gluconeogenesis by stimulating FoxO1 phosphorylation to reduce the expression of downstream G6Pase. Innovatively, molecular docking coupled with different Pull-Down assays revealed that PB2 could directly bind with AKT, Nrf2 and GSK3β, suggesting PB2 may improve IR via regulation of PI3K/AKT-Nrf2-GSK3β signaling, more than FoxO1 signaling pathway; subsequently, Nrf2 could directly bind with GSK3β, reinforcing evidence for PB2-Nrf2-GSK3β complex formation. Besides, co-treatment with PI3K/AKT and Nrf2 inhibitors or siRNAs highlighted the essential role of Nrf2 activation in PB2-contributed IR improvement. Moreover, PB2 has also been validated to exert its effect via regulation of PI3K/AKT-Nrf2-GSK3β signaling pathway in vivo. Therefore, these findings suggest that PB2 is a potent and promising compound to ameliorate glucose metabolism by targeting IR.