In vitro inhibition of glycogen-degrading enzymes and glycosidases by six-membered sugar mimics and their evaluation in cell cultures Original Research Article

We investigated in vitro inhibition of mammalian carbohydrate-degrading enzymes by six-membered sugar mimics and their evaluation in cell cultures. 1-Deoxynojirimycin (DNJ) showed no significant inhibition toward glycogen phosphorylase (GP) but was a potent inhibitor of another glycogen-degrading enzyme, amylo-1,6-glucosidase (1,6-GL), with an IC50 value of 0.16 μM. In primary rat hepatocytes, the inhibition of glycogen breakdown by DNJ reached plateau at 100 μM with 25% inhibition and then remained unchanged. The potent GP inhibitor 1,4-dideoxy-1,4-imino-d-arabinitol (d-AB1) inhibited hepatic glucose production with an IC50 value of about 9 μM and the inhibition by d-AB1 was further enhanced in the presence of DNJ. DNJ and α-homonojirimycin (HNJ) are very potent inhibitors of rat intestinal maltase, with IC50 values of 0.13 and 0.08 μM, respectively, and also showed a similar strong inhibition toward maltase in Caco-2 cell model system, with IC50 value of 0.05 and 0.10 μM, respectively. d-Isofagomine (d-IFG) and l-IFG are competitive and noncompetitive inhibitors of human lysosomal β-glucosidase (β-GL), respectively, with Ki values of 8.4 nM and 6.9 μM. d-IFG increased intracellular β-GL activity by twofold at 10 μM in Gaucher N370S cell line as an ‘active-site-specific’ chaperone, and surprisingly a noncompetitive inhibitor l-IFG also increased intracellular β-GL activity by 1.6-fold at 500 μM.