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This Article Full Text (PDF) All Versions of this Article: 297/6/E1324    most recent ajpendo.00366.2009v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Sorensen, L. Articles by Nielsen, S. PubMed PubMed Citation Articles by Sorensen, L. Articles by Nielsen, S.

RESEARCH ARTICLE

VLDL-TG kinetics: a dual isotope study for quantifying VLDL-TG pool size, production rates and fractional oxidation in humans

¹Dept. M (endocrinology and diabetes), Aarhus University Hospital ²Department of Nuclear Medicine, Aarhus University Hospital, Aarhus, Denmark ³Insitute of Anatomy, University of Aarhus

Submitted 4 June 2009 ; revised 2 September 2009 ; accepted in final form 21 September 2009

Very-low-density-lipoproteins (VLDLs) are large, complex particles containing surface proteins (e.g. ApoB100) and core lipids (e.g. cholesterol and triglycerides). Whereas ApoB100 kinetics has been thoroughly studied, accurate measurement of VLDL-TG kinetics has proven difficult due to either complex mathematics or laborious procedures. The present study was therefore designed to measure VLDL-TG kinetics by dual isotope ex-vivo labeled VLDL-TG tracers and well established kinetics equations (bolus injection or the primed-continuous infusion). Ten healthy caucasian men (age 23±3 years (mean±SD), BMI 24.7±1.3kg/m²) were included in the study. VLDL-TG rate of appearance (Ra) was measured using a dual tracer technique ([9,10-³H]VLDL-TG and [1-¹⁴C]VLDL-TG) to allow comparison of various bolus decay curve fits with the Ra obtained by the primed-continuous infusion (considered the Gold Standard). In addition, VLDL-TG fatty acid oxidation was measured as ¹⁴CO2 in exhaled breath using the hyamine trapping technique. Following a bolus injection, tracer decay was better described by a bi-exponential than a mono-exponential fit (BIEXP: r²=0.99±0.01 vs. MONOEXP: 0.97±0.04, p=0.01). VLDL-TG Ra calculated using the primed-continuous infusion (PCI) correlated significantly with the bi-exponential fit (rho=0.62, p<0.05) whereas this was not the case for the mono-exponential fit (rho=-0.18, p=NS). VLDL-TG Ra using the best fit of the bolus injection method (BIEXP) was less than values obtained by the constant infusion technique (BIEXP: 34.3 (27.1-69.6) vs. PCI: 44.4 (33.0-72.7), p<0.05). Fractional oxidation of VLDL-TG was 37.2±8.8% at 240 min corresponding to 198.8±55.9kcal/day or 10.6±3.3% of resting energy expenditure (REE). Our data demonstrate: 1) that VLDL-TG Ra measured by a biexponential fit to a bolus decay curve correlates well with VLDL-TG Ra measured by a primed-continous infusion, and therefore 2) that a "second" peripheral VLDL-TG compartment with rapid exchange of TG exists. VLDL-TG volume of distribution is therefore greater than previously anticipated. Finally our data supports that 3) VLDL-TG contributes quantitatively to REE.

VLDL-triglycerides; lipoproteins; tracer kinetics; methods