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

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-14C]glucose into glyceride-glycerol, used to evaluate G3P generation via glycolysis, was reduced by ∼26–36% in liver slices of fasted and diabetic rats. The glycolytic flux was reduced by ∼60% in both groups. The incorporation of 1.0 mM [2-14C]pyruvate into glyceride-glycerol (glyceroneogenesis) increased ∼50% and ∼36% in slices of fasted and diabetic rats, respectively, which also showed a two-fold increase in the activity phospho enolpyruvate carboxykinase. The increased incorporation of 1.0 mM [2-14C]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-14C]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 [2-14C]pyruvate and [U-14C]glycerol into glucose of incubation medium (gluconeogenesis) were ∼140 and ∼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 ∼20% of G3P generated for glyceride-glycerol synthesis, the glycolytic pathway with ∼5%, and direct phosphorylation of glycerol by glycerokinase with ∼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.

Lipase-catalyzed esterification of glycerol with n-3 polyunsaturated fatty acids from winterized fish oil Esterificación catalítica de glicerol con ácidos grasos 3-n poliinsaturados de aceite de pescado

Menhaden oil was hydrolyzed using a lipase from Pseudomonas sp. The hydrolysate was cold frac tionated at-72°C. Glyceride synthesis was performed using the same lipase under different reaction environments. The best conditions for the esterification reaction were 39 °C for 18 h in a reaction mixture containing anhydrous glycerol, n-3 polyunsaturated fatty acids (PUFA) enriched solution (2% lipids in hexane), hexane, and phosphate buffer-lipase solution (1% w/v). Product composition was 81.33% triacylglycerides and 18.67% of free fatty acids (w/w). Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) accounted for 36.18% of the esterified fatty acids, of which 58% was EPA and 42% was DHA. This method offers an alternative to produce glycerides rich in n-3 PUFA.