Abstract
Dipeptidyl peptidase 4 (DPP4) inhibitors suppress the metabolism of the potent antihyperglycemic hormone glucagon-like peptide-1 (GLP-1). DPP4 was recently shown to provide cardioprotection through a reduction of infarct size, but the mechanism for this remains elusive. Known interactions between DPP4 and adenosine deaminase (ADA) suggest an involvement of adenosine signaling in DPP4 inhibitor-mediated cardioprotection. We tested whether the protective mechanism of the DPP4 inhibitor alogliptin against myocardial ischemia-reperfusion injury involves GLP-1- and/or adenosine-dependent signaling in canine hearts. In anesthetized dogs, the coronary artery was occluded for 90 min followed by reperfusion for 6 h. A 4-day pretreatment with alogliptin reduced the infarct size from 43.1 ± 2.5% to 17.1 ± 5.0% without affecting collateral flow and hemodynamic parameters, indicating a potent antinecrotic effect. Alogliptin also suppressed apoptosis as demonstrated by the following analysis: 1) reduction in the Bax-to-Bcl2 ratio; 2) cytochrome c release, 3) an increase in Bad phosphorylation in the cytosolic fraction; and 4) terminal deoxynucleotidyl transferase dUTP nick end labeling assay. This DPP4 inhibitor did not affect blood ADA activity or adenosine concentrations. In contrast, the nonselective adenosine receptor blocker 8-(p-sulfophenyl)theophylline (8SPT) completely blunted the effect of alogliptin. Alogliptin did not affect Erk1/2 phosphorylation, but it did stimulate phosphorylation of Akt, glycogen synthase kinase-3β, and cAMP response element-binding protein (CREB). Only 8SPT prevented alogliptin-induced CREB phosphorylation. In conclusion, the DPP4 inhibitor alogliptin suppresses ischemia-reperfusion injury via adenosine receptor- and CREB-dependent signaling pathways.