Human Apolipoprotein (Apo) B-48 and ApoB-100 Kinetics With Stable Isotopes

Abstract

Abstract —The kinetics of apolipoprotein (apo) B-100 and apoB-48 within triglyceride-rich lipoproteins (TRLs) and of apoB-100 within IDL and LDL were examined with a primed-constant infusion of (5,5,5- ² H ₃ ) leucine in the fed state (hourly feeding) in 19 subjects after consumption of an average American diet (36% fat). Lipoproteins were isolated by ultracentrifugation and apolipoproteins by SDS gels, and isotope enrichment was assessed by gas chromatography/mass spectrometry. Kinetic parameters were calculated by multicompartmental modeling of the data with SAAM II. The pool sizes (PS) of TRL apoB-48, VLDL apoB-100, and LDL apoB-100 were 17±10, 273±167, and 3325±1146 mg, respectively. There was a trend toward a faster fractional catabolic rate (FCR) for VLDL apoB-100 than for TRL apoB-48 (6.73±3.48 versus 5.02±2.07 pools/d, respectively, P =0.06). The mean FCRs for IDL and LDL apoB-100 were 10.07±7.28 and 0.27±0.08 pools/d, respectively. The mean production rate (PR) of TRL apoB-48 was 6.5% of VLDL apoB-100 (1.3±0.90 versus 20.06±6.53 mg · kg ⁻¹ · d ⁻¹ , P r =0.780, P r =−0.1810, P =0.458). VLDL apoB-100 PS was correlated with both PR ( r =0.713, P =0.0006) and FCR ( r =−0.692, P =0.001) of VLDL apoB-100 and by apoB-48 PR ( r =0.728, P =0.0004). LDL apoB-100 PS was correlated with FCR ( r =−0.549, P =0.015). These data indicate that (1) the FCRs of TRL apoB-48 and VLDL apoB-100 are similar in the fed state, (2) TRL apoB-48 PS is correlated with TRL apoB-48 PR, (3) VLDL apoB-100 PS is correlated with both PR and FCR of VLDL apoB-100 and PR of TRL apoB-48, and (4) LDL apoB-100 PS is correlated with LDL FCR.