Metabolism of [1,3-C-13]glycerol-1,2,3-tris(methylsuccinate) and glycerol-1,2,3-tris(methyl[2,3-C-13]succinate) in rat hepatocytes

Hepatocytes prepared from overnight-fasted rats were incubated for 120 minu tes in the presence of 2.5 mmol/L [1.3-C-13]glycerol-1,2,3-tris(methylsucci nate) or glycerol-1,2,3-tris(methyl[2,3-C-13]succinate). The identification and quantification of C-13. enriched metabolites by a recently developed m ethod for the deconvolution of nuclear magnetic resonance (NMR) spectra wit h multiplet structures and constraints documented a virtually complete reco very of [1,3-C-13]glycerol-1,2,3-tris(methylsuccinate) in C-13-labeled glyc erol, lactic acid, and glucose. In hepatocytes exposed to [1,3-C-13]glycero l-1,2,3-tris(methylsuccinate), glucose was symmetrically labeled, with the vast majority of hexose molecules being enriched with C-13 On both C-1 and C-3 and/or C-6 and C-4. The respective abundance of glucose isotopomers lab eled either on both C-3 and C-4 or On only 1 of these 2 C atoms indicated t hat the triose phosphates generated from [1,3-C-13]glycerol represented 44% +/- 1% of the total amount of triose phosphates incorporated into the hexo se, In hepatocytes exposed to glycerol-1,2,3-tris(methyl[2,3-C-13]succinate ), the recovery of [2,3-C-13]succinate, [2,3-C-13]fumarate, and either doub le- or single-labeled malate, lactate, alanine, and glucose accounted for a bout half the initial C-13 content of the ester. The majority of the glucos e molecules were now labeled in both C1 and C-2 Or C-6 and C-5, With a pref erential labeling of C-6-C-5 relative to C-1-C-2 the paired C-6/C-1 and C-5 /C-2 ratios averaging 1.33 +/- 0.04. These findings show that glycerol-1,2, 3-tris(methylsuccinate) is efficiently and extensively metabolized in hepat ocytes. They reinforce the concept that the asymmetry of glucose C-13-label ing by triose phosphates generated from Krebs cycle intermediates is modula ted by the availability of glycerol-derived triose phosphates, Lastly, the present study indicates that the latter triose esters, under the present ex perimental conditions which do not aim at duplicating the physiological in vivo situation, are largely directly channelled in the gluconeogenic pathwa y, with only a limited intrahepatic contribution of the "indirect" pathway involving their back-and-forth interconversion to and from pyruvate. Copyri ght (C) 2000 by W.B. Saunders Company.