adenosine-5--(n-ethylcarboxamide) and Diabetes-Mellitus--Type-1

Adenosine A2A receptor (A2AAR) activation plays a major role in the regulation of coronary flow (CF). Recent studies from our laboratory and others have suggested that A2AAR expression and/or signaling is altered in disease conditions. However, the coronary response to AR activation, in particular A2AAR, in diabetes is not fully understood. In this study, we use an STZ mouse model of type 1 diabetes (T1D) to look at CF responses to the nonspecific AR agonist NECA and the A2AAR specific agonist CGS 21680 in-vivo and ex-vivo. Using immunofluorescence, we also explored the effect of diabetes on A2AAR expression in coronary arteries. NECA mediated increase in CF was significantly increased in hearts isolated from STZ-induced diabetic mice. In addition, both in in-vivo and ex-vivo responses to A2AAR activation using CGS 21680 were significantly higher in diabetic mice when compared to their controls. Immunohistochemistry showed an upregulation of A2AAR in both coronary smooth muscle and endothelial cells (~160% and ~140%, respectively). Our data suggest that diabetes resulted in an increased A2AAR expression in coronary arteries which resulted in enhanced A2AAR-mediated increase in CF observed in diabetic hearts. This is the first report implying that A2AAR has a role in the regulation of CF in diabetes, supporting recent studies suggesting that the use of adenosine and its A2A selective agonist (regadenoson, Lexiscan®) may not be appropriate for the detection of coronary artery diseases in T1D and the estimation of coronary reserve.

Topics: Adenosine; Adenosine A2 Receptor Agonists; Adenosine-5'-(N-ethylcarboxamide); Animals; Coronary Circulation; Coronary Vessels; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Endothelial Cells; Gene Expression Regulation; Heart; Humans; Male; Mice; Muscle, Smooth, Vascular; Organ Culture Techniques; Phenethylamines; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Signal Transduction; Vasodilation; Vasodilator Agents

Growing evidence indicates that adenosine receptors could be promising therapeutic targets in autoimmune diseases. Here we studied the role of adenosine receptors in controlling the course of type 1 diabetes. Diabetes in CD-1 mice was induced by multiple-low-dose-streptozotocin (MLDS) treatment and in nonobese diabetic (NOD) mice by cyclophosphamide injection. The nonselective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) prevented diabetes development in both MLDS-challenged mice and in cyclophosphamide-treated NOD mice. The effect of NECA was reversed by the selective A2B receptor antagonist N-(4-cyanophenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)phenoxy]acetamide (MRS 1754). The selective A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA) and A3 receptor agonist N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (IB-MECA) were less efficacious in ameliorating the course of diabetes. NECA inhibited diabetes in A2A receptor KO mice and the selective A2A receptor agonist 2-p-(2-carboxyethyl)phenethyl-amino-5'-N-ethyl-carboxamidoadenosine (CGS21680) had no effect in normal mice, indicating a lack of role of A2A receptors. NECA failed to prevent cytokine-induced beta-cell death in vitro, but NECA strongly suppressed expression of the proinflammatory cytokines TNF-alpha, MIP-1alpha, IL-12, and IFN-gamma in pancreata, endotoxin, or anti-CD3-stimulated splenic cells, and T helper 1 lymphocytes, indicating that the beneficial effect of NECA was due to immunomodulation. These results demonstrate that adenosine receptor ligands are potential candidates for the treatment of type 1 diabetes.

Topics: Adenosine-5'-(N-ethylcarboxamide); Animals; Cells, Cultured; Cytokines; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 1; Gene Amplification; Insulin; Male; Mice; Mice, Inbred NOD; Pancreas; Purinergic P1 Receptor Agonists; Receptors, Purinergic P1; Th1 Cells; Th2 Cells

Platelets from patients with insulin-dependent diabetes with proliferative retinopathy showed the same reactivity to ADP as those from control subjects. Responsiveness of platelets to the aggregation inhibitor adenosine and to the analogue N-ethylcarboxamidoadenosine was decreased in diabetes. In contrast, responsiveness to the anti-aggregatory effects of prostaglandin I2 was not significantly altered in diabetes. Platelets from diabetic patients exhibited decreased formation of cyclic AMP in response to N-ethylcarboxamidoadenosine compared with those from control subjects. In contrast, when adenylyl cyclase was stimulated by prostaglandin I2 or by forskolin, no differences in cyclic AMP formation were observed between control and diabetic platelets. Diabetes was associated with an apparent loss of high-affinity binding of [3H]N-ethylcarboxamidoadenosine to platelet membranes. Possible mechanisms that could contribute to this diabetes-induced change in signalling through the platelet A2 adenosine receptor are discussed.

Topics: Adenosine; Adenosine Diphosphate; Adenosine-5'-(N-ethylcarboxamide); Binding Sites; Blood Platelets; Cell Membrane; Colforsin; Diabetes Mellitus, Type 1; Diabetic Retinopathy; Epoprostenol; Female; GTP-Binding Proteins; Humans; Middle Aged; Platelet Aggregation; Receptors, Purinergic; Signal Transduction