Rapamycin impairs metabolism-secretion coupling in rat pancreatic islets by suppressing carbohydrate metabolism.
Rapamycin, an immunosuppressant used in human transplantation, impairs beta-cell function, but the mechanism is unclear. Chronic (24 h) exposure to rapamycin concentration dependently suppressed 16.7 mM glucose-induced insulin release from islets (1.65+/-0.06, 30 nM rapamycin versus 2.35+/-0.11 ng/islet per 30 min, control, n=30, P<0.01) without affecting insulin and DNA contents. Rapamycin also decreased alpha-ketoisocaproate-induced insulin release, suggesting reduced mitochondrial carbohydrate metabolism. ATP content in the presence of 16.7 mM glucose was significantly reduced in rapamycin-treated islets (13.42+/-0.47, rapamycin versus 16.04+/-0.46 pmol/islet, control, n=30, P<0.01). Glucose oxidation, which indicates the velocity of metabolism in the Krebs cycle, was decreased by rapamycin in the presence of 16.7 mM glucose (30.1+/-2.7, rapamycin versus 42.2+/-3.3 pmol/islet per 90 min, control, n=9, P<0.01). Immunoblotting revealed that the expression of complex I, III, IV, and V was not affected by rapamycin. Mitochondrial ATP production indicated that the respiratory chain downstream of complex II was not affected, but that carbohydrate metabolism in the Krebs cycle was reduced by rapamycin. Analysis of enzymes in the Krebs cycle revealed that activity of alpha-ketoglutarate dehydrogenase (KGDH), which catalyzes one of the slowest reactions in the Krebs cycle, was reduced by rapamycin (10.08+/-0.82, rapamycin versus 13.82+/-0.84 nmol/mg mitochondrial protein per min, control, n=5, P<0.01). Considered together, these findings indicate that rapamycin suppresses high glucose-induced insulin secretion from pancreatic islets by reducing mitochondrial ATP production through suppression of carbohydrate metabolism in the Krebs cycle, together with reduced KGDH activity.
Shimodahira
Makiko
M
Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan.
Fujimoto
Shimpei
S
Mukai
Eri
E
Nakamura
Yasuhiko
Y
Nishi
Yuichi
Y
Sasaki
Mayumi
M
Sato
Yuichi
Y
Sato
Hiroki
H
Hosokawa
Masaya
M
Nagashima
Kazuaki
K
Seino
Yutaka
Y
Inagaki
Nobuya
N
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D050260:Carbohydrate Metabolism / Q000187:drug effects*; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004789:Enzyme Activation / Q000187:drug effects; D005941:Glucokinase / Q000378:metabolism; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D007166:Immunosuppressive Agents / Q000008:administration & dosage*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D007651:Keto Acids / Q000494:pharmacology; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D020123:Sirolimus / Q000008:administration & dosage*
D007166:Immunosuppressive Agents; D007328:Insulin; D007651:Keto Acids; C013082:alpha-ketoisocaproic acid; D000255:Adenosine Triphosphate; D004247:DNA; D005941:Glucokinase; D005947:Glucose; D020123:Sirolimus