Glycogen Phosphorylase Inhibitor N-(3,5-Dimethyl-Benzoyl)-N’-(β-D-Glucopyranosyl)Urea Improves Glucose Tolerance under Normoglycemic and Diabetic Conditions and Rearranges Hepatic Metabolism

Abstract

Glycogen phosphorylase (GP) catalyzes the breakdown of glycogen and largely contributes to hepatic glucose production making GP inhibition an attractive target to modulate glucose levels in diabetes. Hereby we present the metabolic effects of a novel, potent, glucose-based GP inhibitor (KB228) tested in vitro and in vivo under normoglycemic and diabetic conditions. KB228 administration enhanced glucose sensitivity in chow-fed and obese, diabetic mice that was a result of higher hepatic glucose uptake. Besides improved glucose sensitivity, we have observed further unexpected metabolic rearrangements. KB228 administration increased oxygen consumption that was probably due to the overexpression of uncoupling protein-2 (UCP2) that was observed in animal and cellular models. Furthermore, KB228 treatment induced mammalian target of rapamycin complex 2 (mTORC2) in mice. Our data demonstrate that glucose based GP inhibitors are capable of reducing glucose levels in mice under normo and hyperglycemic conditions. Moreover, these GP inhibitors induce accommodation in addition to GP inhibition - such as enhanced mitochondrial oxidation and mTORC2 signaling – to cope with the glucose influx and increased glycogen deposition in the cells, however the molecular mechanism of accommodation is unexplored.

Priming Effect of a Morning Meal on Hepatic Glucose Disposition Later in the Day

“…Our previous work (36) and that of others (37) demonstrated the importance of suppressing GP activity relative to GS activity in the stimulation of HGU and hepatic glucose storage. We examined the hepatic expression of pAkt and PTG in an attempt to identify other regulatory proteins that might have affected glucose uptake and storage in the SAL and GLC groups, but we found no evidence for a differential effect.…”

Glycogen phosphorylase inhibition improves beta cell function

“…Reverse transcription coupled with RT-qPCR reactions were performed similarly as in Nagy et al (2013). Briefly, total RNA was prepared using TRIzol reagent (Invitrogen) according to the manufacturer's instructions.…”

“…The other GPi-s, namely KB228 and BEVA335, were synthesized in the laboratory of Dr L. Somsák (Figure 1 A-C). The inhibitors were used in concentrations close to their K i to ensure pharmacological specificity: KB228 at 3 μM (K i = 937 nM) (Nagy et al, 2013), BEVA335 at 1.5 μM (K i = 411 nM) (Bokor et al, 2013;Bokor et al, 2015) and CP-316819 at 0.5 μM (K i = 220 nM). The K i of CP-316819 was determined using the same methodology (Osz et al, 1999) as that used for KB228 and BEVA335 in order to gain comparable K i values ( Figure 1D).…”

Glucopyranosylidene-spiro-iminothiazolidinone, a new bicyclic ring system: Synthesis, derivatization, and evaluation for inhibition of glycogen phosphorylase by enzyme kinetic and crystallographic methods

“…A variant of E with a 3,5-dimethyl-phenyl group in place of the 2-naphthyl moiety was shown to improve glucose tolerance and to rearrange hepatic metabolism in diabetic mice. 24 These observations shifted the focus of inhibitor design towards interactions in the β-channel and led to new principles 25 stating that efficient inhibitors advantageously have a rigid spirobicyclic scaffold which should not necessarily have an H-bond donor towards His377 (although this can be beneficial if available), but a suitably oriented, large aromatic substituent must be present to fit into the β-channel. These principles were first validated by the synthesis and enzymatic evaluation of glucopyranosylidene-spiro-oxathiazolines 25,26 (e. g. F in Chart 1) and further corroborated by spiro-isoxazolines 27 G among which the 2-naphthyl derivatives proved to be nanomolar inhibitors.…”