title: Measuring VLDL-triglyceride turnover in humans using ex vivo-prepared VLDL tracer.
abstract: There has been more interest in VLDL-triglyceride (TG) kinetics during the last decade. Unfortunately, robust measurement methods are elaborate and not readily available. Here, we describe a method using unique, ex vivo labeling of the 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 that of in vivo-labeled VLDL-TG and that turnover rates can be safely estimated from the log linear decay of VLDL-TG specific activity. We found minor labeling of the plasma FFA (oleate) pool, which was largely attributable to coinfusion of free [14C]triolein; VLDL-TG did not contribute substantially to the 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 h 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.
authors.affiliation: Medical Department M (Endocrinology and Diabetes), Aarhus University Hospital, DK-8000 Aarhus, Denmark.
authors.forename: Lars C
authors.initials: LC
authors.lastname: Gormsen
authors.forename: Michael D
authors.initials: MD
authors.lastname: Jensen
authors.forename: Søren
authors.initials: S
authors.lastname: Nielsen
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000328:Adult; D001693:Biological Transport, Active; D002250:Carbon Radioisotopes; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007262:Infusions, Intravenous; D007700:Kinetics; D008079:Lipoproteins, VLDL / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D019301:Oleic Acid / Q000097:blood / Q000378:metabolism; D010084:Oxidation-Reduction; D014280:Triglycerides / Q000097:blood* / Q000378:metabolism; D014304:Triolein / Q000008:administration & dosage / Q000378:metabolism; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D005230:Fatty Acids, Nonesterified; D008079:Lipoproteins, VLDL; D014280:Triglycerides; C030106:very low density lipoprotein triglyceride; D014316:Tritium; D014304:Triolein; D019301:Oleic Acid