Effects of prolonged in vitro exposure to sulphonylureas on the function and survival of human islets

The direct effects of prolonged exposure to sulphonylureas on the function and survival of human islets are unknown. This study assessed the insulin content, glucose-stimulated insulin release, islet cell apoptosis, and mRNA expression of insulin and GLUT-1 in isolated human islets cultured in the presence of therapeutical concentrations of glimepiride (10 muM), glibenclamide (10 muM), or chlorpropamide (600 muM). Islets were prepared by collagenase digestion and density gradient purification from 18 multiorgan donors and were then exposed for 24 h to the different sulphonylureas. Insulin content decreased significantly following culture with any sulphonylurea compound. In response to an acute challenge with 3.3 and 16.7 mM glucose, insulin release from the control islets accounted for 1.9 +/- 0.5% and 4.9 +/- 1.7% of total insulin content (P < .01), respectively. Glucose responsiveness was preserved in islets precultured in the presence of glimepiride, whereas high glucose level did not elicit any significant increase of insulin secretion from islets preincubated with glibenclamide or chlorpropamide. These alterations were reverted by an additional 48-h incubation in drug-free conditions. The amount of apoptotic cells did not differ significantly among the experimental groups. Quantitative RT-PCR studies showed that, compared with the control islets, cells preincubated with glibenclamide or chlorpropamide had an increased expression of insulin mRNA, with no change in the expression of GLUT-1. In conclusion, prolonged exposure of human islets to different sulphonylureas causes different disturbances of islet cell function, with glimepiride showing milder effects, as compared with chlorpropamide and glibenclamide. (C) 2005 Elsevier Inc. All rights reserved