Submitted on January 11, 2006
Revised on February 22, 2006
Accepted on March 23, 2006
Use of Intralipid for kinetic analysis of HDL apoC-III: evidence for a homogeneous kinetic pool of apoC-III in plasma
Minh N. Nguyen, Dick C. Chan, Kevin P. Dwyer, Paul Bolitho, Gerald F. Watts, and P. Hugh R. Barrett
Metabolic Research Centre, School of Medicine and Pharmacology, University of Western Australia, Perth, Western Australia 6847
Corresponding Author: Hugh.Barrett{at}uwa.edu.au
Apolipoprotein CIII is an important regulator of lipoprotein metabolism. Radioisotope and stable isotope kinetic studies show differing results in relation to the kinetics of apoC-III in HDL. Kinetic analysis of HDL apoC-III may be difficult due to its low concentration, as well as the presence of other apoproteins at higher concentration, in the HDL fraction. We used Intralipid (IL), known to preferentially extract apoC proteins from plasma, as a means of extracting apoC-III from HDL prior to apoprotein separation by isoelectric focusing gel electrophoresis for the measurement of tracer enrichment. Protein purity was assessed by an isoleucine to leucine (Ile/Leu) ratio, as apoC-III contains no isoleucine. We compared apoC-III kinetics in 14 men using a bolus infusion of deuterated leucine. The Ile/Leu ratio for IL-extracted HDL (IL-HDL) apoC-III (3.0 ± 0.7%) was not different to that of VLDL apoC-III (2.6 ± 0.6%), but was significantly lower than untreated HDL apoC-III (9.0 ± 2.9%) (p<0.001). The isotopic enrichment curves and fractional catabolic rates (FCR) for IL-HDL apoC-III were not different to those of VLDL apoC-III. In contrast, HDL apoC-III had significantly lower isotopic enrichments and FCRs than IL-HDL apoC-III (p<0.001). In conclusion, this simple IL method can be used to isolate apoC-III from HDL with minimal interference from other HDL apoproteins and demonstrates that the kinetics of apoC-III in VLDL and HDL are similar, supporting the concept of a single kinetically homogeneous pool of apoC-III in plasma.