Metabolism of alpha-D-[1,2-C-13]glucose pentaacetate and alpha-D-glucose penta[2-C-13]acetate in rat hepatocytes

摘要

Hepatocytes from fed rats were incubated for 120 min in the presence of alpha-D-[1,2-C-13]glucose pentaacetate (1.7 mM), both D-[1,2-C-13]glucose (1.7 mM) and acetate (8.5 mM), alpha-D-glucose penta[2-C-13]acetate (1.7 mM), or D-[1,2-C-13]glucose (8.3 mM). The amounts of C-13-enriched L-lactate and D-glucose and those of acetate and beta-hydroxybutyrate recovered in the incubation medium were comparable under the first two experimental conditions. The vast majority of D-glucose isotopomers consisted of alpha- and beta-D[1,2-C-13]glucose. The less abundant single-labeled isotopomers of D-glucose were equally labeled on each C atom. The output of C-13-labeled L-lactate, mainly L[2-C-13]lactate and L-[3-C-13]lactate, was 1 order of magnitude lower than that found in hepatocytes exposed to 8.3 mM D-[1,2-C-13]glucose, in which case the total production of the single-labeled species of D-glucose was also increased and that of the C-3- or C-4-labeled hexose was lower than that of the other C-13-labeled isotopomers. In cells exposed to alpha-D-glucose penta[2-C-13]acetate, the large majority of C-13 atoms was recovered as [2-C-13]acetate and, to a much lesser extent, beta-hydroxybutyrate labeled in position 2 and/or 4. Nevertheless, L-[2-C-13]lactate, L-[3-C-13]lactate, and single-labeled D-glucose isotopomers were also produced in amounts higher or comparable to those found in cells exposed to alpha-D-[1,2-C-13]glucose pentaacetate. However, a modest preferential labelling of the C-6-C-5-C-4 moiety of D-glucose, relative to its C-1-C-2-C-3 moiety, and a lesser isotopic enrichment of the C-3 (or C-4), relative to that of C-1 (or C-6) and C-2 (or C-5), were now observed. These findings indicate that, despite extensive hydrolysis of cu-D-glucose pentaacetate (1.7 mM) in the hepatocytes, the catabolism of its D-glucose moiety is not more efficient than that of unesterified D-glucose, tested at the same molar concentration (1.7 mM) in the presence of the same molar concentration of unesterified acetate (8.5 mM), and much lower than that found at a physiological concentration of the hexose (8.3 mM). The present results also argue against any significant back-and-forth interconversion of D-glucose 6-phosphate and triose phosphates, under conditions in which sizeable amounts of D-glucose are formed de novo from C-13-enriched Krebs cycle intermediates generated from either D-[1,2-C-13]glucose or [2-C-13]acetate. (C) 2000 Academic Press. [References: 16]