A novel natural PPAR gamma agonist, Gypenoside LXXV, ameliorates cognitive deficits by enhancing brain glucose uptake via the activation of Akt/GLUT4 signaling in db/db mice

Targeting the PPAR gamma might be a potential therapeutic strategy for diabetes-associated cognitive decline (DACD). In this study, Gypenoside LXXV (GP-75), a dammarane-type triterpene compound isolated from Gynostemma pentaphyllum, was found to be a novel PPAR gamma agonist using a dual-luciferase reporter assay system. However, whether GP-75 has protective effects against DACD remains unknown. Interestingly, intragastric administration of GP-75 (40 mg/kg/day) for 12 weeks significantly attenuated the cognitive deficit in db/db mice. GP-75 treatment significantly improved the glucose tolerance and lipid metabolism, and suppressed neuroinflammation. Notably, GP-75 treatment dramatically increased the uptake of glucose by the brain, as detected by F-18-FDG PET. Incubation of primary cortical neurons with GP-75 significantly increased 2-deoxyglucose uptake. In addition, GP-75 treatment markedly increased the p-Akt (Ser 473)/total Akt levels and the expression levels of PPAR gamma and GLUT4, while decreasing the levels of p-IRS-1 (Ser 616)/total IRS-1. Importantly, all of these protective effects mediated by GP-75 were abolished by cotreatment with the PPAR gamma antagonist, GW9662. However, GP-75-mediated PPAR gamma upregulation was not affected by coincubation with the phosphatidylinositol 3-kinase inhibitor, LY294002. Collectively, GP-75 might be a novel PPAR gamma agonist that ameliorates cognitive deficit by enhancing brain glucose uptake via the activation of Akt/GLUT4 signaling in db/db mice.