A Convenient LC-MS Method for Assessment of Glucose Kinetics In Vivo with D-[13C6]Glucose as a Tracer

BACKGROUND: The isotope-labeled intravenous glucose tolerance test (IVGTT) combined with computer modeling is widely used to derive parameters related to glucose metabolism in vivo. Most of these methods involve use of either H-2(2)-labeled or C-13(1)-labeled D-glucose as a tracer with GC-MS to measure the isotope enrichment. These methods are challenging, both technologically and economically. We have developed a novel approach that is suitable for labeled-IVGTT studies involving a large cohort of individuals. METHODS: The tracer, D-[C-13(6)] glucose, is a low-cost alternative with the significant advantage that the sixth isotope of natural glucose has virtually zero natural abundance, which facilitates isotopomer analysis with <10% labeled glucose in the infusate. After deproteinization of plasma samples collected at various times, glucose is converted to a stable derivative, purified by solid-phase extraction (SPE), and analyzed by HPLCelectrospray ionization mass spectrometry to accumulate the isotope-abundance data for the A+2, A+3, and A+6 ions of the glucose derivative. A 2-pool modeling program was used to derive standard kinetic parameters. RESULTS: With labeled-IVGTT data from 10 healthy male individuals, the values for insulin sensitivity, glucose effectiveness, and the plasma clearance rate estimated with the 2-pool minimal model compared well with values obtained via traditional methods. CONCLUSIONS: The relative simplicity and robustness of the new method permit the preparation and analysis of up to 48 samples/day, a throughput equivalent to 2 complete IVGTT experiments, and this method is readily adaptable to existing 96 well-format purification and analytical systems. (C) 2008 American Association for Clinical Chemistry