Functional and Molecular Defects of Pancreatic Islets in Human Type 2 Diabetes

Functional and Molecular Defects of Pancreatic Islets in Human Type 2 Diabetes Silvia Del Guerra , Roberto Lupi , Lorella Marselli , Matilde Masini , Marco Bugliani , Simone Sbrana , Scilla Torri , Maria Pollera , Ugo Boggi , Franco Mosca , Stefano Del Prato and Piero Marchetti From the Department of Endocrinology and Metabolism, Metabolic Unit, Cisanello Hospital, Pisa, Italy Address correspondence and reprint requests to Piero Marchetti MD, Department of Endocrinology and Metabolism, Metabolic Unit, Ospedale Cisanello, Via Paradisa 2, 56124 Pisa, Italy. E-mail marchant{at}immr.med.unipi.it Abstract To shed further light on the primary alterations of insulin secretion in type 2 diabetes and the possible mechanisms involved, we studied several functional and molecular properties of islets isolated from the pancreata of 13 type 2 diabetic and 13 matched nondiabetic cadaveric organ donors. Glucose-stimulated insulin secretion from type 2 diabetic islets was significantly lower than from control islets, whereas arginine- and glibenclamide-stimulated insulin release was less markedly affected. The defects were accompanied by reduced mRNA expression of GLUT1 and -2 and glucokinase and by diminished glucose oxidation. In addition, AMP-activated protein kinase activation was reduced. Furthermore, the expression of insulin was decreased, and that of pancreatic duodenal homeobox-1 (PDX-1) and forkhead box O1 (Foxo-1) was increased. Nitrotyrosine and 8-hydroxy-2′-deoxyguanosine concentrations, markers of oxidative stress, were significantly higher in type 2 diabetic than control islets, and they were correlated with the degree of glucose-stimulated insulin release impairment. Accordingly, 24-h exposure to glutathione significantly improved glucose-stimulated insulin release and decreased nitrotyrosine concentration, with partial recovery of insulin mRNA expression. These results provide direct evidence that the defects of insulin secretion in type 2 diabetic islets are associated with multiple islet cell alterations. Most importantly, the current study shows that the functional impairment of type 2 diabetic islets can be, at least in part, reversible. In this regard, it is suggested that reducing islet cell oxidative stress is a potential target of human type 2 diabetes therapy. AMPK, AMP-activated protein kinase Foxo-1, forkhead box O1 GSH, glutathione GSSG, GSH disulfide KRB, Krebs-Ringer bicarbonate solution 8-OHdG, 8-hydroxy-2′-deoxyguanosine PDX-1, pancreatic d