Glibenclamide Treatment Recruits β-Cell Subpopulation Into Elevated and Sustained Basal Insulin Synthetic Activity

Abstract

Use of sulfonylureas in diabetes treatment is based on their insulin-releasing effect on pancreatic ␤-cells. Prolonged action is known to degranulate ␤-cells, but functional consequences have not been examined at the cellular level. This study investigates influences of in vivo (48-h) and in vitro (24-h) glibenclamide treatment on the functional state of the ␤-cell population. Both conditions decreased cellular insulin content by >50% and caused an elevated basal insulin biosynthetic activity that was maintained for at least 24 h after drug removal. Glibenclamide stimulation of basal insulin synthesis was not achieved after a 2-h exposure; it required a calcium-dependent translational activity and involved an increase in the percent activated ␤-cells (50% after glibenclamide pretreatment vs. 8% in control cells). The glibenclamide-activated ␤-cell subpopulation corresponded to the degranulated ␤-cell subpopulation that was isolated by fluorescenceactivated cell sorter on the basis of lower cellular sideward scatter. Glibenclamide pretreatment did not alter cellular rates of glucose oxidation but sensitized ␤-cells to glucoseinduced changes in metabolic redox and insulin synthesis and release. In conclusion, chronic exposure to glibenclamide results in degranulation of a subpopulation of ␤-cells, which maintain an elevated protein and insulin synthetic activity irrespective of the presence of the drug and of glucose. Our study demonstrates that the in situ ␤-cell population also exhibits a functional heterogeneity that can vary with drug treatment. Glibenclamide induces degranulated ␤-cells with a sustained elevated basal activity that might increase the risk for hypoglycemic episodes. Diabetes 55:78 -85, 2006 P revious studies (1-9) led us to propose that the normal pancreatic ␤-cell population exhibits intercellular differences that are functionally relevant, in particular for generating the normal dose-response curves to glucose. Chronic exposure to high glucose was found to reduce intercellular differences in glucose sensitivity and thus decrease the net effect of an acute glucose stimulation (7,10,11). Since this view is mainly based on in vitro studies, its potential relevance for the in situ endocrine pancreas needs to be addressed in in vivo models. There are a few reports in which differences among ␤-cells have been described in the intact pancreas, mostly in terms of the intensity of cellular staining for insulin (12,13). After treatment of rats with the insulin secretagogue glibenclamide, the degranulation of ␤-cells was not homogenous (12,13). This observation might thus disclose in situ differences in cellular responsiveness to the drug and in subsequent functional activity. The present work examines this possibility by investigating the ␤-cells that are isolated from glibenclamide-treated rats and comparing them with ␤-cells isolated from normal control rats either without or with a preincubation with glibenclamide. The data indicate that glibenclamide treatment causes a degranulation in a subpopula...

Glibenclamide activates translation in rat pancreatic beta cells through calcium-dependent mTOR, PKA and MEK signalling pathways

“…Glibenclamide induced similar effects when administered to beta cell cultures for 24 h but not for 2 h. The elevated rate of insulin synthesis was not associated with an increase in insulin mRNA content [3], which was different from the studies of Yamato et al [4,5] showing enhanced insulin gene expression in rat islets following exposure to glibenclamide. It appeared to involve a calcium-dependent activation of translation; it was not seen at low extracellular calcium concentrations or in the presence of the calcium channel blocker verapamil or of the translation inhibitor cycloheximide [3]. Taken together, these observations indicate that the functional responsiveness of the pancreatic beta cell population at a particular time is influenced by the translational activity of the cells during the preceding day.…”

“…The glibenclamide-recruited beta cells were degranulated, indicating that they had also been activated for insulin secretion [3]. Glibenclamide induced similar effects when administered to beta cell cultures for 24 h but not for 2 h. The elevated rate of insulin synthesis was not associated with an increase in insulin mRNA content [3], which was different from the studies of Yamato et al [4,5] showing enhanced insulin gene expression in rat islets following exposure to glibenclamide. It appeared to involve a calcium-dependent activation of translation; it was not seen at low extracellular calcium concentrations or in the presence of the calcium channel blocker verapamil or of the translation inhibitor cycloheximide [3].…”

“…This form of regulation also occurs in vivo as was recently shown in glibenclamidetreated rats [3]. A 2 day treatment with this sulfonylurea drug recruited a beta cell subpopulation into an elevated and sustained basal insulin synthetic activity and thus influenced the shape of the subsequent glucose doseresponse curve [3]. The glibenclamide-recruited beta cells were degranulated, indicating that they had also been activated for insulin secretion [3].…”

“…The intercellular differences in glucose sensitivity can be altered by culture at low or high glucose concentrations with subsequent changes in functional responsiveness [2]. This form of regulation also occurs in vivo as was recently shown in glibenclamidetreated rats [3]. A 2 day treatment with this sulfonylurea drug recruited a beta cell subpopulation into an elevated and sustained basal insulin synthetic activity and thus influenced the shape of the subsequent glucose doseresponse curve [3].…”

“…A 2 day treatment with this sulfonylurea drug recruited a beta cell subpopulation into an elevated and sustained basal insulin synthetic activity and thus influenced the shape of the subsequent glucose doseresponse curve [3]. The glibenclamide-recruited beta cells were degranulated, indicating that they had also been activated for insulin secretion [3]. Glibenclamide induced similar effects when administered to beta cell cultures for 24 h but not for 2 h. The elevated rate of insulin synthesis was not associated with an increase in insulin mRNA content [3], which was different from the studies of Yamato et al [4,5] showing enhanced insulin gene expression in rat islets following exposure to glibenclamide.…”