Effects of starvation and diabetes on the metabolism of [2,3- 13C]succinic acid dimethyl ester in rat hepatocytes

Abstract

The metabolism of [2,3- 13C]succinic acid dimethyl ester ([2,3- 13C]-SAD) 10 mmol/L was examined in hepatocytes from overnight-fasted normal rats, 3-day starved rats, and overnight-fasted hereditarily diabetic Goto-Kakizaki (GK) rats. The amount of 13C-labeled succinate, fumarate, malate, lactate, alanine, and aspartate released by the hepatocytes was much higher in fasted normal rats than in starved or diabetic animals. Although the integrated areas of the 13C 2 and 13C 3 signals assigned to double-labeled malate, lactate, or alanine were not significantly different, the amount of single-labeled malate, lactate, alanine, and aspartate was higher in C 3- versus C 2-labeled isotopomers. The release of 13C-labeled glucose by the hepatocytes was lower in fasted versus starved or diabetic rats. Virtually all hexose molecules double-labeled in the C 1-C 2-C 3 and/or C 6-C 5-C 4 moieties corresponded to the [1,2- 13C] and/or [5,6- 13C]isotopomers. However, in the case of the single-labeled species, 13C-labeling of C 1 (or C 6) exceeded that of C 2 (or C 5). Both the single- and double-labeled molecules enriched with 13C in the C 1-C 2-C 3 moiety were less abundant than those labeled in the C 6-C 5-C 4 moiety, with such asymmetry being most marked in overnight-fasted normal rats, less pronounced in diabetic animals, and virtually absent in starved rats. These findings document that SAD is efficiently metabolized in hepatocytes, with its use as a gluconeogenic precursor being influenced by the nutritional and hormonal status of the animals. The present experiments also reinforce the view that asymmetrical labeling of glucose by 13C-labeled precursors is modulated by the relative contribution of exogenous and endogenous nutrients to the production of triose phosphates incorporated into the hexose.