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

Stable isotope methodology was used to determine the kinetic behavior of ap olipoprotein (apo) A-I within the triglyceride-rich lipoprotein (TRL) fract ion 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) o ver the age of 40 were placed on a baseline average American diet and after 6 weeks received a primed-constant infusion of [5,5,5,5,5-H-2(3)]-L-leucin e 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 obtain ed by gas chromatography-mass spectrometry, Data were fitted to a compartme ntal model to determine the fractional secretion rates of apoA-I and apoB-4 8 within each lipoprotein fraction. Mean plasma apoA-I levels in TRL and HD L fractions were 0.204 +/- 0.057 and 134 +/- 15 mg/dl, respectively. The me an fractional catabolic rate (FCR) of TRL apoA-I was 0.250 +/- 0.069 and HD L apoA-I was 0.239 +/- 0.054: pools/day, with mean estimated residence time s (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 result s 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 simila r rates.