Chronic exposure to beta-hydroxybutyrate inhibits glucose-induced insulin release from pancreatic islets by decreasing NADH contents.
To investigate the effects of chronic exposure to ketone bodies on glucose-induced insulin secretion, we evaluated insulin release, intracellular Ca2+ and metabolism, and Ca2+ efficacy of the exocytotic system in rat pancreatic islets. Fifteen-hour exposure to 5 mM d-beta-hydroxybutyrate (HB) reduced high glucose-induced insulin secretion and augmented basal insulin secretion. Augmentation of basal release was derived from promoting the Ca2+-independent and ATP-independent component of insulin release, which was suppressed by the GDP analog. Chronic exposure to HB affected mostly the second phase of glucose-induced biphasic secretion. Dynamic experiments showed that insulin release and NAD(P)H fluorescence were lower, although the intracellular Ca2+ concentration ([Ca2+](i)) was not affected 10 min after exposure to high glucose. Additionally, [Ca2+](i) efficacy in exocytotic system at clamped concentrations of ATP was not affected. NADH content, ATP content, and ATP-to-ADP ratio in the HB-cultured islets in the presence of high glucose were lower, whereas glucose utilization and oxidation were not affected. Mitochondrial ATP production shows that the respiratory chain downstream of complex II is not affected by chronic exposure to HB, and that the decrease in ATP production is due to decreased NADH content in the mitochondrial matrix. Chronic exposure to HB suppresses glucose-induced insulin secretion by lowering the ATP level, at least partly by inhibiting ATP production by reducing the supply of NADH to the respiratory chain. Glucose-induced insulin release in the presence of aminooxyacetate was not reduced, which implies that chronic exposure to HB affects the malate/aspartate shuttle and thus reduces NADH supply to mitochondria.
Takehiro
Mihoko
M
Dept. of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
Fujimoto
Shimpei
S
Shimodahira
Makiko
M
Shimono
Dai
D
Mukai
Eri
E
Nabe
Koichiro
K
Radu
Razvan Gheorghe
RG
Kominato
Rieko
R
Aramaki
Yo
Y
Seino
Yutaka
Y
Yamada
Yuichiro
Y
D020155:3-Hydroxybutyric Acid / Q000494:pharmacology*; D000222:Adaptation, Physiological / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D009243:NAD / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D004791:Enzyme Inhibitors; D007328:Insulin; D009243:NAD; D005947:Glucose; D002118:Calcium; D020155:3-Hydroxybutyric Acid