Reproducibility of stable isotope labeled tracer measures of VLDL-triglyceride and VLDL-apolipoprotein B-100 kinetics

Faidon Magkos, Bruce W. Patterson, and Bettina Mittendorfer

Internal Medicine, WashingtonUniversity School of Medicine, St Louis, MO 63110

Corresponding Author: mittendb{at}medicine.wustl.edu

Derangements in plasma lipid metabolism are common in obese and diabetic subjects and predispose them to cardiovascular disease. To gain insight into the mechanisms responsible for alterations in plasma lipid homeostasis, FFA, VLDL-triglyceride (TG) and VLDL-apolipoprotein B-100 (apoB-100) kinetics are commonly assessed by using stable isotope labeled tracer methods. The reproducibility of these measurements, which is critical for the experimental design and interpretation of the data, is unknown. We therefore investigated the reproducibility of plasma FFA, VLDL-TG, and VLDL-apoB-100 kinetics in eight healthy men by using stable isotope labeled tracer techniques. Each subject was studied on two different occasions, after an overnight fast. There were no systematic differences in plasma FFA, VLDL-TG, and VLDL-apoB-100 concentrations and kinetics between the two studies. The intra-individual day-to-day variability for various outcome variables ranged from ~15% to ~25%; based on our assessment of the analytical variability, almost all of the day-to-day variability is of biological origin (>92%). The most robust outcome variables were FFA rate of appearance in plasma and hepatic VLDL-TG and VLDL-apoB-100 secretion rates; the least robust were VLDL-TG and VLDL-apoB-100 plasma clearance rates and mean residence times. This suggests that the factors involved in the control of VLDL-TG and VLDL-apoB-100 secretion by the liver may be less variable than those regulating intravascular metabolism and removal of VLDL-TG and VLDL-apoB-100 from the circulation. Overall, physiologically meaningful differences in mean values (i.e., =25-30% in magnitude) can be obtained with a sample size of 6-10 subjects for paired studies and 12-20 subjects per group for cross-sectional studies, assuming a type-I error rate of 0.05 and a type-II error rate of 0.20 (i.e., 80% power). These findings will be useful for future studies investigating FFA, VLDL-TG, and VLDL-apoB-100 kinetics with the methods described.

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