Submitted on May 19, 2005
Revised on October 11, 2005
Accepted on October 17, 2005
Measuring VLDL-triglycerides turnover in humans using ex-vivo prepared VLDL tracer
Lars C. Gormsen, Michael D. Jensen, and Soren Nielsen
Endocrine Research Unit, Mayo Clinic, Rochester, MN 55905
Corresponding Author: jensen.michael{at}mayo.edu
There has been more interest in Very-Low-Density-Lipoprotein (VLDL) triglyceride (TG) kinetics during the last decade. Unfortunately, robust measurement methods are elaborate and not readily available. Herein we describe a method utilizing unique, ex-vivo, labeling of fatty acid moiety of VLDL-TG followed by intravenous bolus infusion in the same person. We found that plasma disappearance of ex-vivo labeled VLDL-TG was comparable to in-vivo labeled VLDL-TG and that turnover rates can be safely estimated from log linear decay of VLDL-TG specific activity. We found minor labeling of plasma free fatty acid (FFA) (oleate) pool, which was largely attributed to co-infusion of free [14C]triolein; VLDL-TG did not contribute substantially to plasma FFA pool. The plasma decay curve of VLDL-TG was not affected by the presence of tracer in the FFA pool provided that the data from 2 hours after the VLDL tracer bolus infusion was used. The FFA contamination problem was circumvented by minor modification of the VLDL-TG tracer preparation. The approach we describe should expand the opportunity to study processes that cannot be assessed if the FFA precursor pool is labeled. This method for VLDL-TG tracer preparation can allow measurement of VLDL turnover, tissue uptake of VLDL-TG, and oxidation of VLDL-TG.
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