Effects of a glucokinase activator on hepatic intermediary metabolism: study with 13C-isotopomer-based metabolomics

Abstract

GKAs (glucokinase activators) are promising agents for the therapy of Type 2 diabetes, but little is known about their effects on hepatic intermediary metabolism. We monitored the fate of 13C-labelled glucose in both a liver perfusion system and isolated hepatocytes. MS and NMR spectroscopy were deployed to measure isotopic enrichment. The results demonstrate that the stimulation of glycolysis by GKA led to numerous changes in hepatic metabolism: (i) augmented flux through the TCA (tricarboxylic acid) cycle, as evidenced by greater incorporation of 13C into the cycle (anaplerosis) and increased generation of 13C isotopomers of citrate, glutamate and aspartate (cataplerosis); (ii) lowering of hepatic [Pi] and elevated [ATP], denoting greater phosphorylation potential and energy state; (iii) stimulation of glycogen synthesis from glucose, but inhibition of glycogen synthesis from 3-carbon precursors; (iv) increased synthesis of N-acetylglutamate and consequently augmented ureagenesis; (v) increased synthesis of glutamine, alanine, serine and glycine; and (vi) increased production and outflow of lactate. The present study provides a deeper insight into the hepatic actions of GKAs and uncovers the potential benefits and risks of GKA for treatment of diabetes. GKA improved hepatic bioenergetics, ureagenesis and glycogenesis, but decreased gluconeogenesis with a potential risk of lactic acidosis and fatty liver.

The Molecular and Metabolic Influence of Long Term Agmatine Consumption

“…Measurement was performed on either an Agilent Triple Quad 6410 mass spectrometer combined with an Agilent LC 1260 Infinity or Hewlett-Packard 5971 Mass Selective Detector coupled with a 5890 HP-GC, GC-MS Agilent System (6890 GC-5973 Mass Selective Detector) or a Hewlett-Packard HP-5970 Mass Selective Detector using electron impact ionization with an ionizing voltage of Ϫ70 eV and an electron multiplier set to 2000 V as described previously (22). Levels of free Car and Car/AcylCar profiling both in blood and various tissues were determined using tandem mass spectrometry as described (23,25).…”

“…A separate group of rats given SD or SD ϩ AGM for 4 weeks was used to prepare isolated hepatocytes as we described (22 (3,22). A separate series of incubations was carried out in medium as described (23) to determine the activity of ␥-butyrobetaine dioxygenase (␥-BBD), the enzyme that catalyzes the last step of Car synthesis (23,24).…”

“…Measurements of 13 CO 2 release following incubation of isolated hepatocytes were performed by isotope ratio mass spectrometry (3,22). The concentration of hepatic N-acetylglutamate (NAG) was determined as indicated (3,26).…”

Glucokinase activation is beneficial or toxic to cultured rat pancreatic islets depending on the prevailing glucose concentration

“…If GKAs undoubtedly trigger liver steatosis (4,6,34), their potential toxicity to ␤-cells remains unclear (4,35,38,43,44,46). Thus, although some GKAs proved beneficial to ␤-cell survival and GSIS under glucotoxic conditions and in islets from T2D patients (8,35,46), their secondary failure during long-term treatment (22,31,47) reopened the question of their toxicity to ␤-cells.…”

Novel and emerging diabetes mellitus drug therapies for the type 2 diabetes patient

“…GK functions as a glucose sensor in pancreatic β cells, thereby stimulating glucose-stimulated insulin secretion and regulating glucose metabolism within the liver, including gluconeogenesis, glycolysis, glycogen synthesis, glucose oxidation, lipogenesis, urea, and uric acid production [43,[45][46][47][48] .…”