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Journal of Lipid Research, Vol. 47, 1274-1280, June 2006
Copyright © 2006 by American Society for Biochemistry and Molecular Biology

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. Barrett¹

Metabolic Research Centre, School of Medicine and Pharmacology, University of Western Australia, Perth, Western Australia

Published, JLR Papers in Press, March 23, 2006.

¹ To whom correspondence should be addressed. e-mail: hugh.barrett{at}uwa.edu.au

Apolipoprotein C-III (apoC-III) 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 because of 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 before 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 from that of VLDL apoC-III (2.6 ± 0.6%) but was significantly lower than that of untreated HDL apoC-III (9.0 ± 2.9%) (P < 0.001). The isotopic enrichment curves and fractional catabolic rates (FCRs) for IL-HDL apoC-III were not different from 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 it 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.

Supplementary key words high density lipoprotein • very low density lipoprotein • gas chromatography-mass spectrometry • lipoprotein metabolism • apolipoprotein C-III

Abbreviations: apoC-III, apolipoprotein C-III; d₃-leucine, deuterated leucine; FCR, fractional catabolic rate; IEF, isoelectric focusing; IL, Intralipid®; Ile/Leu, isoleucine-to-leucine; PR, production rate; PVDF, polyvinylidene difluoride; TRL, triglyceride-rich lipoprotein; TTR, tracer-to-tracee ratio

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