Human apolipoprotein A-I kinetics within triglyceride-rich lipoproteins and high density lipoproteins

Abstract

Stable isotope methodology was used to determine the kinetic behavior of apolipoprotein (apo) A-I within the triglyceride-rich lipoprotein (TRL) fraction and to compare TRL apoA-I kinetics with that of apoA-I in high density lipoprotein (HDL) and TRL apoB-48. Eight subjects (5 males and 3 females) over the age of 40 were placed on a baseline average American diet and after 6 weeks received a primed-constant infusion of [5,5,5-2H3]-l-leucine for 15 h while consuming small hourly meals of identical composition. HDL and TRL apoA-I and TRL apoB-48 tracer/tracee enrichment curves were obtained by gas chromatography–mass spectrometry. Data were fitted to a compartmental model to determine the fractional secretion rates of apoA-I and apoB-48 within each lipoprotein fraction. Mean plasma apoA-I levels in TRL and HDL fractions were 0.204 ± 0.057 and 134 ± 15 mg/dl, respectively. The mean fractional catabolic rate (FCR) of TRL apoA-I was 0.250 ± 0.069 and HDL apoA-I was 0.239 ± 0.054 pools/day, with mean estimated residence times (RT) of 4.27 and 4.37 days, respectively. The mean TRL apoB-48 FCR was 5.2 ± 2.0 pools/day and the estimated mean RT was 5.1 ± 1.8 h. Our results indicate that apoA-I is catabolized at a slower rate than apoB-48 within TRL, and that apoA-I within TRL and HDL fractions are catabolized at similar rates.—Vélez-Carrasco, W., A. H. Lichtenstein, P. H. R. Barrett, Z. Sun, G. G. Dolnikowski, F. K. Welty, and E. J. Schaefer. Human apolipoprotein A-I kinetics within triglyceride-rich lipoproteins and high density lipoproteins. J. Lipid Res. 1999. 40: 1695–1700.

Keywords

• apoA-I
• apoB-48
• kinetics
• stable isotopes
• TRL
• compartmental analysis