Different (13)CO(2) recovery of orally administered [1-(13)C]- and [8-(13)C] triolein in postprandial humans: an effect of phosphoenolpyruvate-carboxykinase (EC 4.1.1.32) in peripheral tissues?
In this study the conversion of orally administered [1-(13)C]- and [8-(13)C]triolein to CO(2) was compared in normal postprandial human subjects (3 female, 3 male). After an overnight fast the subjects consumed hourly meals of a liquid formula diet over 12 h (8.3% of the predicted 24 h resting energy expenditure/h). 90 min after the first meal on one occasion a bolus of [1-(13)C]triolein was given and in the repeat study the same subject received [8-(13)C]triolein. The order of isotope substrate was randomized. Isotope ratio mass spectrometry analysis of breath samples an recorded CO(2) production rate resulted in a significant 1.31 times greater (13)CO(2) recovery of [1-(13)C]triolein compared to [8-(13)C]triolein within 7.5 h. 10 h after bolus the significant difference disappeared. The different (13)CO(2) recovery is probably due to a different metabolic fate of (13)C at odd and even numbered carbon positions in the fatty acid chain caused by beta-oxidation, citric acid cycle and the phosphoenolpyruvate carboxykinase (EC 4.1.1.32) reaction in peripheral tissues. A contribution of a chain shortening in peroxisomes seems unlikely.
Metges
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Institute of Nutritional Science, Technical University of Munich, 85350 Freising-Weihenstephan, Germany.
Wolfram
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