Korean Diabetes Journal 2004;28(6):490-500.
Published online December 1, 2004.
The Effect of cAMP-Elevating Agents on High Glucose-Induced Apoptosis of Isolated Islets of Rat Pancreas.
Gwan Pyo Koh, Kwang Sik Suh, Suk Chon, Seung Joon Oh, Jeong Taek Woo, Sung Woon Kim, Jin Woo Kim, Young Seol Kim, Sun Hee Kwon
1Department of Endocrinology & Metabolism, College of Medicine, Kyung Hee University, Korea.
2Research Institute of Endocrinology, Kyung Hee University, Korea.
3Department of Internal Medicine, Dong Su Won General Hospital, Korea.
High glucose-induced apoptosis has been implicated in the loss of beta-cells of the pancreatic islets in animal models of type 2 diabetes. GLP-1 has been shown to reduce apoptosis by the cAMP-dependent mechanism in beta-cells. Other studies have also shown that elevated levels of intracellular cyclic AMP delayed apoptosis in other types of cells. We investigated whether cAMP-elevating agents could suppress the high glucose-induced apoptosis of isolated rat islets. METHODS: Pancreatic islets were isolated from Sprague-Dawley (SD) rats. The expression of phosphodiesterase (PDE) 3 subtypes was investigated by using extracts of freshly isolated islets and analyzing them by RT-PCR. After 2 days of isolation, the islets were cultured in RPMI-1640 media containing 5% FBS with various glucose concentrations (11.1, 16.7 and 27.8 mM), 5x10-6 M forskolin, 2x10-4 M 3-isobutyl-1-methylxanthine (IBMX), 10-5 M cilostazol, and 10-6, 5x10-6 and 10-5 M H-89 for 5 days. The islet apoptosis was measured by a sandwich enzyme-immunoassay using antihistone antibody. RESULTS: Apoptosis was lowest at 11.1 mM glucose concentration, and increased at higher glucose concentrations (1.00 +/- 0.04 A.U. (arbitrary unit) at 11.1 mM, 1.17 +/- 0.12 A.U. at 16.7 mM, and 1.65 +/-0.13 A.U. at 27.8 mM (P <0.05 for 11.1 mM). Both PDE 3A and 3B mRNA were expressed in the islet extracts. In 16.7 and 27.8 mM glucose concentrations, forskolin (P <0.01), IBMX (P <0.05) and cilostazol (P < 0.05) suppressed apoptosis of the islet cells. Protein kinase A (PKA) nhibitor, H-89, did not prevent the inhibition of apoptosis by forskolin. CONCLUSION: These results show that high glucose-induced apoptosis of the cells in rat islet is attenuated by such cAMP-elevating agents as cilostazol. However, cyclic AMP regulation of islet apoptosis may occur via a PKA-independent signaling pathway.
Key Words: Glucose toxicity, Beta-cell, Apoptosis, cAMP, Cilostazol, Protein kinase A

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