Use of multiple 13C-labeling strategies and 13C NMR to detect low levels of exogenous metabolites in the presence of large endogenous pools: measurement of glucose turnover in a human subject.
A significant problem which may be encountered in 13C NMR studies of metabolism is the contribution that background levels of 13C may make to the observed spectra when low or tracer levels of the 13C label are used. We propose that the introduction of two or more labeled sites in the same tracer molecule is an effective strategy for eliminating or reducing this difficulty and demonstrate its feasibility in an isotope dilution study of glucose turnover in a human volunteer. This approach has two significant advantages over the more common use of a singly enriched labeling strategy: (i) as a consequence of the scalar coupling interactions, multiple-labeled metabolites will yield spectra distinct from those containing natural abundance 13C, and (ii) at a 99% level of enrichment for the precursor, concentration levels which are approximately 1% of the endogenous pools can be detected with approximately equal sensitivity. As a demonstration of this strategy, glucose production in a human subject was determined by continuous infusion of tracer levels of [U-13C6]glucose over a 4-h period and subsequent analysis of plasma levels of the tracer in vitro by NMR. Mass spectroscopy was used on the same samples to provide a basis for comparison of the precision and accuracy of the NMR technique. The results demonstrate the feasibility of the multiply labeled approach for detection by NMR of tracer amounts of label in the presence of a much larger endogenous pool of glucose. The NMR and mass spectrometric data gave quantitatively identical results for the glucose production rate demonstrating that equivalent data may be obtained by both methods.(ABSTRACT TRUNCATED AT 250 WORDS)
Brainard
J R
JR
Isotope and Nuclear Chemistry Division, University of California, Los Alamos National Laboratory, New Mexico 87545.
Downey
R S
RS
Bier
D M
DM
London
R E
RE
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002247:Carbon Isotopes; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013058:Mass Spectrometry
D001786:Blood Glucose; D002247:Carbon Isotopes; D005947:Glucose