Lipoproteins containing the truncated apolipoprotein, Apo B-89, are cleared from human plasma more rapidly than Apo B-100-containing lipoproteins in vivo.
We have reported previously on two truncations of apolipoprotein B (apo B-40 and apo B-89) in a kindred with hypobetalipoproteinemia. Premature stop codons were found to be responsible for both apo B-40 and apo B-89, but the physiologic mechanisms accounting for the reduced plasma concentrations of these proteins have not been determined in vivo. This study investigates the metabolism of apo B-89 in two subjects heterozygous for apo B-89/apo B-100 and in one apo B-40/apo B-89 compound heterozygote. In both heterozygotes total apo B concentration is approximately 30% of normal and apo B-89 is present in lower concentrations in plasma than apo B-100. After the administration of [1-13C]leucine as a primed constant infusion over 8 h, 13C enrichments of plasma leucine as well as enrichments of VLDL-, IDL-, and LDL-apo B-89 leucine and VLDL-, IDL-, and LDL-apo B-100 leucine were measured over 110 h. Enrichment values were subsequently converted to tracer/tracee ratios and a multicompartmental model was used to estimate metabolic parameters. In both apo B-89/apo B-100 heterozygotes apo B-89 and apo B-100 were produced at similar rates. Respective transport rates of apo B-89 and apo B-100 for subject 1 were 2.13 +/- 0.18 and 2.56 +/- 0.13 mg.kg-1.d-1, and for subject 2, 6.59 +/- 0.18 and 8.23 +/- 0.39 mg.kg-1.d-1. However, fractional catabolic rates of VLDL, IDL, and LDL particles containing apo B-89 were 1.4-3 times higher than the rates for corresponding apo B-100-containing particles. Metabolic parameters of apo B-89 in the apo B-40/apo B-89 compound heterozygote compared favorably with those established for apo B-89 in apo B-89/apo B-100 heterozygotes. Thus, the enhanced catabolism of VLDL, IDL, and LDL particles containing the truncated apolipoprotein is responsible for the relatively low levels of apo B-89 seen in these subjects.
Parhofer
K G
KG
Division of Atherosclerosis and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110.
Barrett
P H
PH
Bier
D M
DM
Schonfeld
G
G
D000328:Adult; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000097:blood*; D005260:Female; D006579:Heterozygote; D006801:Humans; D006995:Hypobetalipoproteinemias / Q000097:blood* / Q000235:genetics; D007700:Kinetics; D008074:Lipoproteins / Q000097:blood* / Q000737:chemistry; D008297:Male; D008875:Middle Aged
D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D008074:Lipoproteins; C068393:apolipoprotein B-89