title: Glucose suppresses superoxide generation in metabolically responsive pancreatic beta cells.
abstract: High rates of glucose metabolism and mitochondrial electron transport have been associated with increased mitochondrial production of reactive oxygen species (ROS). This mechanism was also proposed as a possible cause for dysfunction and death of pancreatic beta cells exposed to high glucose levels. We examined whether high rates of glucose metabolism increase ROS production in purified rat beta cells. Glucose up to 20 mm did not stimulate H(2)O(2) or superoxide production, whereas it dose-dependently increased cellular NAD(P)H and FADH(2) levels with an EC(50) around 8 mm. On the contrary, glucose concentration-dependently suppressed H(2)O(2) and superoxide formation, with a major effect between 0 and 5 mm, parallel to an increase in cellular NAD(P)H levels. This suppressive effect was more marked in beta cells with higher NAD(P)H responsiveness to glucose; it was not observed in glucagon-containing alpha cells, which lacked a glucose-induced increase in NAD(P)H. Suppression was also induced by the mitochondrial substrates leucine and succinate. Experiments with electron transport chain inhibitors indicate a role of respiratory complex I in ROS production at low mitochondrial activity and low NADH levels. Superoxide production at low glucose is potentially cytotoxic, because scavenging by the superoxide dismutase mimetic agent manganese(III)tetrakis(4-benzoic acid)porphyrin was found to reduce the rate of beta cell apoptosis. Analysis of islets cultured at 20 mm glucose confirmed that this condition does not induce ROS production in beta cells as a result of their increased rates of glucose metabolism. Our study indicates the need of beta cells for basal nutrients maintaining mitochondrial NADH production at levels that suppress ROS accumulation from an inadequate respiratory complex I activity and thus inhibit a potential apoptotic pathway.
authors.affiliation: Diabetes Research Center, Brussels Free University-VUB, Laarbeeklaan 103, B-1090 Brussels, Belgium.
authors.forename: Geert A
authors.initials: GA
authors.lastname: Martens
authors.forename: Ying
authors.initials: Y
authors.lastname: Cai
authors.forename: Simon
authors.initials: S
authors.lastname: Hinke
authors.forename: Geert
authors.initials: G
authors.lastname: Stangé
authors.forename: Mark
authors.initials: M
authors.lastname: Van de Casteele
authors.forename: Daniel
authors.initials: D
authors.lastname: Pipeleers
mesh_terms: D000818:Animals; D017209:Apoptosis; D002374:Catalase / Q000235:genetics; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D042967:Electron Transport Complex I / Q000037:antagonists & inhibitors / Q000502:physiology; D005182:Flavin-Adenine Dinucleotide / Q000031:analogs & derivatives* / Q000378:metabolism; D005934:Glucagon / Q000032:analysis; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D005979:Glutathione Peroxidase / Q000235:genetics; D006861:Hydrogen Peroxide / Q000378:metabolism; D007515:Islets of Langerhans / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism*; D007700:Kinetics; D007930:Leucine / Q000494:pharmacology; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019802:Succinic Acid / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism*; D000094765:Glutathione Peroxidase GPX1
chemical_list: D012333:RNA, Messenger; D009243:NAD; D013481:Superoxides; D005182:Flavin-Adenine Dinucleotide; C058805:1,5-dihydro-FAD; D009249:NADP; D005934:Glucagon; D019802:Succinic Acid; D006861:Hydrogen Peroxide; D002374:Catalase; D005979:Glutathione Peroxidase; D042967:Electron Transport Complex I; D007930:Leucine; D005947:Glucose; D000094765:Glutathione Peroxidase GPX1; C000722069:Gpx1 protein, rat