A novel DPP‐4 inhibitor Gramcyclin A attenuates cognitive deficits in APP/PS1/tau triple transgenic mice via enhancing brain GLP‐1‐dependent glucose uptake

Abstract Enhancing glucagon‐like peptide 1 (GLP‐1) signaling with a dipeptidyl peptidase IV (DPP‐4) inhibitor might exert protective effects on Alzheimer's disease (AD). We found that intragastric administration of Gramcyclin A (10, 20 and 40 mg/kg), a novel DPP‐4 inhibitor, for 3 months significantly reversed cognitive decline in APP/PS1/tau triple transgenic mice in a dose‐dependent manner. Gramcyclin A treatment markedly reduced Aβ plaques as well as the insoluble and soluble forms of Aβ40 and Aβ42 in the hippocampus of APP/PS1/tau mice. Treatment with Gramcyclin A remarkedly decreased the level of microglia and suppressed neuroinflammation in the hippocampus of APP/PS1/tau mice. Moreover, Gramcyclin A treatment could increase brain glucose uptake in APP/PS1/tau mice, as detected by 18‐fluoro‐2‐deoxyglucose ( 18 F‐FDG) micro‐positron emission tomography (micro‐PET) imaging. Furthermore, Gramcyclin A significantly increased expression of glucagon‐like peptide‐1 (GLP‐1), GLP‐1R, proliferator‐activated receptor gamma coactivator (PGC)‐1α and glucose transporter 4 (GLUT4), and inhibited insulin receptor (IRS)‐1 phosphorylation and tau hyperphosphorylation in the hippocampus of APP/PS1/tau mice. Collectively, Gramcyclin A conferred protective effects against AD via enhancing brain GLP‐1‐dependent glucose uptake. The DPP‐4 inhibitor Gramcyclin A might be a potential therapeutic drug for AD.