title: Monomethylated-adenines potentiate glucose-induced insulin production and secretion via inhibition of phosphodiesterase activity in rat pancreatic islets.
abstract: Monomethyladenines have effects on DNA repair, G-protein-coupled receptor antagonism and autophagy. In islet ß-cells, 3-methyladenine (3-MA) has been implicated in DNA-repair and autophagy, but its mechanism of action is unclear. Here, the effect of monomethylated adenines was examined in rat islets. 3-MA, N6-methyladenine (N6-MA) and 9-methyladenine (9-MA), but not 1- or 7-monomethylated adenines, specifically potentiated glucose-induced insulin secretion (3-4 fold; p ≤ 0.05) and proinsulin biosynthesis (∼2-fold; p ≤ 0.05). Using 3-MA as a 'model' monomethyladenine, it was found that 3-MA augmented [cAMP]i accumulation (2-3 fold; p ≤ 0.05) in islets within 5 minutes. The 3-, N6- and 9-MA also enhanced glucose-induced phosphorylation of the cAMP/protein kinase-A (PKA) substrate cAMP-response element binding protein (CREB). Treatment of islets with pertussis or cholera toxin indicated 3-MA mediated elevation of [cAMP]i was not mediated via G-protein-coupled receptors. Also, 3-MA did not compete with 9-cyclopentyladenine (9-CPA) for adenylate cyclase inhibition, but did for the pan-inhibitor of phosphodiesterase (PDE), 3-isobutyl-1-methylxanthine (IBMX). Competitive inhibition experiments with PDE-isoform specific inhibitors suggested 3-MA to have a preference for PDE4 in islet ß-cells, but this was likely reflective of PDE4 being the most abundant PDE isoform in ß-cells. In vitro enzyme assays indicated that 3-, N6- and 9-MA were capable of inhibiting most PDE isoforms found in ß-cells. Thus, in addition to known inhibition of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3'K)/m Target of Rapamycin (mTOR) signaling, 3-MA also acts as a pan-phosphodiesterase inhibitor in pancreatic ß-cells to elevate [cAMP]i and then potentiate glucose-induced insulin secretion and production in parallel.
authors.affiliation: a The Kovler Diabetes Center; Department of Medicine; Section on Endocrinology, Diabetes & Metabolism; The University of Chicago ; Chicago , IL USA.
authors.forename: Brandon B
authors.initials: BB
authors.lastname: Boland
authors.affiliation: a The Kovler Diabetes Center; Department of Medicine; Section on Endocrinology, Diabetes & Metabolism; The University of Chicago ; Chicago , IL USA.
authors.forename: Cristina
authors.initials: C
authors.lastname: Alarcón
authors.affiliation: a The Kovler Diabetes Center; Department of Medicine; Section on Endocrinology, Diabetes & Metabolism; The University of Chicago ; Chicago , IL USA.
authors.forename: Almas
authors.initials: A
authors.lastname: Ali
authors.affiliation: a The Kovler Diabetes Center; Department of Medicine; Section on Endocrinology, Diabetes & Metabolism; The University of Chicago ; Chicago , IL USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Rhodes
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000225:Adenine; D000242:Cyclic AMP; D005947:Glucose; D007328:Insulin; D010726:Phosphodiesterase Inhibitors; C025946:3-methyladenine; C013115:9-methyladenine; C000730567:6-methyladenine
keywords: cAMP; insulin secretion; islets; monomethyladenines; phosphodiesterase; proinsulin biosynthesis