The effect of glucose on the potency of two distinct glycogen phosphorylase inhibitors

Abstract

Two distinct glycogen phosphorylase inhibitors, 5-chloro-1H-indole-2-carboxylic acid [1-(4-fluorobenzyl)-2-(4-hydroxy-piperidin-1-yl)-2-oxoethyl]amide (CP-320,626) and 1,4-dideoxy-1,4-D-arabinitol (DAB), were characterized in vitro with respect to the influence of glucose on their potencies. CP-320,626 has previously been shown to bind to a newly characterized indole site, whereas DAB seems to act as a glucose analogue, but with slightly different properties from those of glucose. When analysed in pig liver glycogen phosphorylase a (GPa) activity assays, the two inhibitors showed very different properties. When GPa activity was measured in the physiological direction (glycogenolysis), DAB was the most potent inhibitor with an IC(50) value of 740+/-9 nM compared with the IC(50) value for CP-320-626 of 2.39+/-0.37 microM. There was no effect of glucose on the inhibitory properties of DAB, whereas a glucose analogue N-acetyl-beta-D-glucopyranosylamine (1-GlcNAc) antagonized the effect of DAB. Likewise, there was no synergistic effect of CP-320,626 and glucose, whereas CP-320,626 and 1-GlcNAc inhibited GPa in synergy. Moreover, the synergistic effect of glucose and CP-320,626 was GPa-isoform-specific, since CP-320,626 and glucose inhibited rabbit muscle GPa in synergy when the GPa activity was measured towards glycogenolysis. When GPa activity was measured towards glycogen synthesis, CP-320,626 showed a synergistic effect with glucose, whereas the effect of DAB was slightly antagonized by glucose in this assay direction. Caffeine was included in the investigation as a control GP inhibitor, and both glucose and 1-GlcNAc potentiated the effect of caffeine independent of the assay direction. In primary cultured rat hepatocytes 1-GlcNAc and CP-320,626 inhibited basal and glucagon-induced glycogenolysis in synergy, whereas the ability of DAB to inhibit basal or glucagon-induced glycogenolysis was unaltered by 1-GlcNAc. Glucose had no effect on either CP-320,626 or DAB inhibition of glycogenolysis in cultured rat hepatocytes. In conclusion, the present study shows that the two GP inhibitors are kinetically very distinct and neither of the inhibitors demonstrates a physiologically relevant glucose dependence in vitro.

Role of β-Adrenoceptors in Memory Consolidation: β3-Adrenoceptors Act on Glucose Uptake and β2-Adrenoceptors on Glycogenolysis

“…As noradrenaline promotes glycogenolysis (Magistretti, 1988;Subbarao and Hertz, 1990;Sorg and Magistretti, 1991;Coopersmith and Leon, 1995), the action of b-AR agonists b-ARs in central metabolism and memory ME Gibbs et al was challenged with the glycogen phosphorylase inhibitor DAB that prevents glycogen breakdown (Andersen et al, 1999;Andersen and Westergaard, 2002). We have shown that administration of DAB interferes with memory processing (Gibbs et al, 2006a).…”

Rac1 Protein Regulates Glycogen Phosphorylase Activation and Controls Interleukin (IL)-2-dependent T Cell Proliferation

“…To explore this possibility, the enzymatic activity of PYGM was measured as described under "Experimental Procedures" (41,42). Briefly, the glucose 1-phosphate produced by PYGM is converted to glucose 6-phosphate by the enzyme phosphoglucomutase.…”

“…Activity Assay for Glycogen Phosphorylase-A glycogen phosphorylase activity assay was performed as indicated (41,42) with some modifications. Briefly, cells were washed twice with cold PBS and resuspended in 500 l of TES buffer (20 mM Tris, pH 7.4, 1 mM EDTA, 225 mM sucrose, 2.5 mM DTT, 0.1 mM PMSF, 1 g/ml leupeptin, 1 g/ml aprotinin).…”

Glycogen Phosphorylase a Inhibitors with a Phenethylphenylphthalimide Skeleton Derived from Thalidomide-Related .ALPHA.-Glucosidase Inhibitors and Liver X Receptor Antagonists

“…The substituent effects of hydroxyl/methoxy groups in the 4Ј-cinnamyl derivatives (13)(14)(15) were quite different from those of phenethylphenylphthalimide derivatives, i.e., the GPa-inhibitory activity decreased in the order of: non-substitutedϾdimethoxyϾdihydroxy derivatives [13Ͼ14ϭ15].…”

“…1), which has been used widely as a commercially available control compound for the structural development studies of GP-inhibitors. [12][13][14] DAB (2) inhibits hepatic glycogen breakdown in vivo and has an anti-hyperglycemic effect, which was found to be most pronounced in obese mice. 12) We have been engaged in the creation of bioactive compounds based on multi-template approach utilizing thalidomide (3) (Fig.…”