A high carbohydrate-fat free diet alters the proportion of heparin-bound VLDL in plasma and the expression of VLDL-apoB-100 epitopes

Abstract

High carbohydrate-fat free diets (CHO-diet) induce the secretion of increased numbers of very-low-density lipoprotein (VLDL) particles and alter the composition and metabolism of VLDL. The aims of this study were to examine VLDL in greater detail, specifically to document any CHO-diet-induced alterations of apolipoprotein B-100 (apoB-100) epitope expression of VLDL, and any changes induced in subclasses of VLDL, as defined by heparin Sepharose chromatography. Fifteen normolipidemic subjects participated in the study by eating a basal typical American diet for 7 days and high carbohydrate diet (85% carbohydrate, <1% fat) for another 7 days. The sequence was changed in seven subjects. Fasting blood samples were analyzed for lipoprotein lipid and apoprotein concentrations. Heparin affinity VLDL subclasses were characterized chemically and electrophoretically [sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE)]. Immunoreactivities of apoB in VLDL were tested in solid phase competitive-binding radioimmunoassays (RIAs) using five monoclonal anti-B antibodies that react with defined epitopes of apoB-100. The CHO diet produced consistent increases of plasma triglycerides in all subjects by a mean of 66% and decreases in plasma cholesterol by 18%. ApoB in plasma decreased by 21% and apoA-I by 17%; however, apoE and ApoA-II did not change. VLDL was enriched with triglycerides (55.0% ± 0.8 v 57.0% ± 0.7, P < .05) and apoE (3.7% ± 0.5 to 5.9% ± 0.7, P < .007) and the ratio between apoE and apoC in VLDL increased (0.15 ± 0.03 to 0.25 ± 0.03, P < .002). In RIAs with monoclonal antibodies (MoAbs) B1B3 and B1B6 that define epitopes located near the LDL receptor recognition region of apoB-100, CHO-VLDL showed decreased immunoreactivity (ED 50s, in μg/mL, rose from 3.9 ± 1.0 to 5.4 ± 1.6, P < .03 and 3.8 ± 0.9 to 6.4 ± 1.3, P < .02, respectively). RIAs using the other three MoAbs with epitopes located in the middle and near the amino terminus of apoB-100 demonstrated no significant changes. The proportion of VLDL not bound by the heparin column was increased from 0.137 ± 0.02 on the basal diet to 0.23 ± 0.03 on CHO diet ( P < .009) and the unbound CHO-VLDL contained more phosphatidylethanolamine relative to sphingomyelin (1.54 ± 0.2 to 2.32 ± −0.2, P < .009). Our data suggest that diets may have differential affects on these two subpopulations of VLDL.