Glyceroneogenesis and the supply of glycerol-3-phosphate for glyceride-glycerol synthesis in liver slices of fasted and diabetic rats

Abstract

The pathways of glycerol-3-phosphate (G3P) generation for glyceride synthesis were examined in precision-cut liver slices of fasted and diabetic rats. The incorporation of 5 mM [U-(14)C]glucose into glyceride-glycerol, used to evaluate G3P generation via glycolysis, was reduced by approximately 26-36% in liver slices of fasted and diabetic rats. The glycolytic flux was reduced by approximately 60% in both groups. The incorporation of 1.0 mM [2-(14)C]pyruvate into glyceride-glycerol (glyceroneogenesis) increased approximately 50% and approximately 36% in slices of fasted and diabetic rats, respectively, which also showed a two-fold increase in the activity phosphoenolpyruvate carboxykinase. The increased incorporation of 1.0 mM [2-(14)C]pyruvate into glyceride-glycerol by slices of fasted rats was not affected by the addition of 5 mM glucose to the incubation medium. The activity of glycerokinase and the incorporation of 1 mM [U-(14)C]glycerol into glyceride-glycerol, evaluators of G3P formation by direct glycerol phosphorylation, did not differ significantly from controls in slices of the two experimental groups. Rates of incorporation of 1 mM [2-(14)C]pyruvate and [U-(14)C]glycerol into glucose of incubation medium (gluconeogenesis) were approximately 140 and approximately 20% higher in fasted and diabetic slices than in control slices. It could be estimated that glyceroneogenesis by liver slices of fasted rats contributed with approximately 20% of G3P generated for glyceride-glycerol synthesis, the glycolytic pathway with approximately 5%, and direct phosphorylation of glycerol by glycerokinase with approximately 75%. Pyruvate contributed with 54% and glycerol with 46% of gluconeogenesis. The present data indicate that glyceroneogenesis has a significant participation in the generation of G3P needed for the increased glyceride-glycerol synthesis in liver during fasting and diabetes.

Increased Glyceride–Glycerol Synthesis in Liver and Brown Adipose Tissue of Rat: In‐Vivo Contribution of Glycolysis and Glyceroneogenesis

“…4). Previous in vitro experiments have shown that a reduction in the G3P generation via glycolysis is accompanied by a significant activation of glyceroneogenesis in liver slices during fasting [11]. We have also previously demonstrated in vitro that G3P synthesis from glucose is increased and glyceroneogenesis is reduced in IBAT from cafeteria-diet-fed rats [9].…”

“…1 Sources and pathways of glycerol-3-phosphate generation in adipose tissue and the liver and possible systemic recycling of fatty acids medium, respectively; both pathways are increased in the liver from fasted and diabetic rats [11]. In both situations, the glycolytic flux (estimated by the amount of 3 H recovered from water after incubation of liver slices in medium containing 3 H-glucose) and the generation of G3P from glucose (assayed by the rate of 14 C-glucose incorporation into glyceride-glycerol) are reduced in the liver slices [11]. These primarily in vitro findings from WAT, BAT and liver suggest that glyceroneogenesis and glycolysis would be reciprocally regulated to ensure the generation of G3P that is necessary for FA esterification and TAG synthesis.…”

“…Recently, in-vivo experiments have indicated that glyceroneogenesis in rat WAT is the major pathway for glyceride-glycerol synthesis [6][7][8]. In vitro studies have suggested that glyceroneogenesis is also physiologically significant in BAT and liver [9][10][11].…”

“…In hepatic tissue, glyceroneogenesis and gluconeogenesis can be simultaneously evaluated in vitro by the rate of incorporation of 14 C-pyruvate into glyceride-glycerol and by the amount of glucose released into the incubation Fig. 1 Sources and pathways of glycerol-3-phosphate generation in adipose tissue and the liver and possible systemic recycling of fatty acids medium, respectively; both pathways are increased in the liver from fasted and diabetic rats [11]. In both situations, the glycolytic flux (estimated by the amount of 3 H recovered from water after incubation of liver slices in medium containing 3 H-glucose) and the generation of G3P from glucose (assayed by the rate of 14 C-glucose incorporation into glyceride-glycerol) are reduced in the liver slices [11].…”

The nuclear retinoid-related orphan receptor-α regulates adipose tissue glyceroneogenesis in addition to hepatic gluconeogenesis

“…Reduced hepatic de novo lipogenesis, as a result of reduced SREBP-1c and FAS, could indeed participate in reduced VLDL production and storage of TG inside adipocytes, thereby reducing adiposity. Regarding liver glyceroneogenesis, it was estimated by Martins-Santos et al (33) that it would contribute to only 20% of the G3P generated for TG synthesis in the liver of fasted rats. To evaluate that point in our mice, we compared pyruvate incorporation into the liver of fasted WT and ROR sg/sg mice (n ϭ 4).…”