Stable isotope tracer dilution for quantifying very low-density lipoprotein-triacylglycerol kinetics in man.
OBJECTIVE
A number of approaches have been employed in the past to measure very low-density lipoprotein (VLDL) triacylglycerol (TG) kinetics in humans in vivo, varying in the selection of tracer and mode of administration. All, however, make use of labeled TG precursors and more or less complicated mathematical models to derive the kinetic parameters of interest. The aim of the present study was to develop a conceptually straightforward method, based on the traditional tracer infusion technique, for quantifying VLDL-TG production rates in man using stable isotopes.


METHODS
Our approach involves ingestion of [U-13C3]glycerol to endogenously label the glycerol in VLDL-TG, plasmapheresis, isolation of the newly 13C-labeled VLDL from plasma, and administration within the next 2-3 days via a primed constant autologous reinfusion. This procedure produces enough tracer for a priming dose plus 2-3 h of infusion. In the physiological conditions examined (basal and hyperglycemic states, fat- and carbohydrate-rich diets), with almost 3-fold ranging VLDL-TG pool sizes, a steady state in plasma VLDL-TG glycerol tracer-to-tracee ratio was readily achieved within 2 h. Consequently, calculations are made according to the isotope dilution principle, thus avoiding assumptions implicit in more complicated models.


CONCLUSIONS
The stable isotope VLDL-TG tracer dilution method offers an alternative and reliable tool for the determination of endogenous VLDL-TG kinetics in man under a variety of metabolic states.
Laboratory of Nutrition and Clinical Dietetics, Department of Nutrition and Dietetics, Harokopio University, 70 El. Venizelou Ave, 17671 Athens, Greece. lsidossis@hua.gr
Labros S
LS
Sidossis
Faidon
F
Magkos
Bettina
B
Mittendorfer
Robert R
RR
Wolfe
D000328:Adult; D002247:Carbon Isotopes; D005990:Glycerol / Q000008:administration & dosage / Q000737:chemistry*; D006801:Humans; D007262:Infusions, Intravenous; D007553:Isotope Labeling / Q000379:methods*; D008079:Lipoproteins, VLDL / Q000378:metabolism / Q000493:pharmacokinetics*; D008297:Male; D019518:Postprandial Period; D014280:Triglycerides / Q000378:metabolism / Q000493:pharmacokinetics*
D002247:Carbon Isotopes; D008079:Lipoproteins, VLDL; D014280:Triglycerides; D005990:Glycerol