Diabetes Abolishes Morphine-Induced Cardioprotection via Multiple Pathways Upstream of Glycogen Synthase Kinase-3β

Abstract

The cardioprotective effect of opioids or glycogen synthase kinase (GSK) inhibitors given at reperfusion has not been investigated in diabetes models. Therefore, nondiabetic (NDBR) or streptozotocin-induced diabetic (DBR) rat hearts were subjected to 30 min of ischemia and 2 h of reperfusion. Groups of NDBR or DBR were administered either vehicle, morphine (0.3 mg/kg), or the GSK inhibitor SB216763 (0.6 mg/kg) 5 min before reperfusion. SB216763 (but not morphine) reduced infarct size in DBRs (44 ± 1* and 55 ± 2%, respectively), while both agents reduced infarct size in NDBRs versus untreated NDBRs or DBRs (44 ± 3*, 42 ± 3*, 60 ± 2, and 56 ± 2%, respectively, *P < 0.001). Morphine-induced phospho- (P-)GSK3β was reduced 5 min after reperfusion in DBRs compared with NDBRs (0.83 ± 0.29 and 1.94 ± 0.12 [P < 0.05] pg/μg tissue, respectively). The GSK3β mediators, P-Akt, P–extracellular signal–related kinase (ERK)1, and P–signal transducer and activator of transcription (STAT)3, were also significantly reduced in untreated DBR compared with NDBR rats. Morphine-induced elevations of P-Akt, P-ERK1, P-p70s6, P–janus-activated kinase-2, and P-STAT3 in NDBRs were also blunted in DBRs. H9C2 cells raised in 25 mmol/l compared with 5.56 mmol/l glucose media also demonstrated reduced morphine-induced P-GSK3β, P-Akt, P-STAT3, and P-ERK1 after 15 min. Hence, acute GSK inhibition may provide a novel therapeutic strategy for diabetic patients during an acute myocardial infarction, whereas morphine is less effective due to signaling events that adversely affect GSK3β.