Abstract
The present study was undertaken to elucidate the metabolic basis for the increased remnants and lipoprotein(a) [Lp(a)] and decreased LDL apolipoprotein B (apoB) levels in human apoE deficiency. A primed constant infusion of (13)C(6)-phenylalanine was administered to a homozygous apoE-deficient subject. apoB-100 and apoB-48 were isolated, and tracer enrichments were determined by gas chromatography-mass spectrometry, then kinetic parameters were calculated by multicompartmental modeling. In the apoE-deficient subject, fractional catabolic rates (FCRs) of apoB-100 in VLDL and intermediate density lipoprotein and apoB-48 in VLDL were 3x, 12x, and 12x slower than those of controls. On the other hand, the LDL apoB-100 FCR was increased by 2.6x. The production rate of VLDL apoB-100 was decreased by 45%. In the Lp(a) kinetic study, two types of Lp(a) were isolated from plasma with apoE deficiency: buoyant and normal Lp(a). (125)I-buoyant Lp(a) was catabolized at a slower rate in the patient. However, (125)I-buoyant Lp(a) was catabolized at twice as fast as (131)I-normal Lp(a) in the control subjects. In summary, apoE deficiency results in: 1) a markedly impaired catabolism of VLDL/chylomicron and their remnants due to lack of direct removal and impaired lipolysis; 2) an increased rate of catabolism of LDL apoB-100, likely due to upregulation of LDL receptor activity; 3) reduced VLDL apoB production; and 4) a delayed catabolism of a portion of Lp(a).
Highlights
The present study was undertaken to elucidate the metabolic basis for the increased remnants and lipoprotein(a) [Lp(a)] and decreased LDL apolipoprotein B levels in human Apolipoprotein E (apoE) deficiency
The plasma cholesterol level of 442 mg/dl was disproportionately higher than the TG level of 171 mg/dl
The intermediate density lipoprotein (IDL) T/T ratio increased and decayed very slowly during and after the infusion period in the apoE-deficient subject (Fig. 2A), whereby the IDL apoB-100 T/T is almost indistinguishable from the LDL apoB-100 T/T curve
Summary
The present study was undertaken to elucidate the metabolic basis for the increased remnants and lipoprotein(a) [Lp(a)] and decreased LDL apolipoprotein B (apoB) levels in human apoE deficiency. In the apoE-deficient subject, fractional catabolic rates (FCRs) of apoB-100 in VLDL and intermediate density lipoprotein and apoB-48 in VLDL were 3؋, 12؋, and 12؋ slower than those of controls. In the Lp(a) kinetic study, two types of Lp(a) were isolated from plasma with apoE deficiency: buoyant and normal Lp(a). ApoE deficiency results in: 1) a markedly impaired catabolism of VLDL/chylomicron and their remnants due to lack of direct removal and impaired lipolysis; 2) an increased rate of catabolism of LDL apoB-100, likely due to upregulation of LDL receptor activity; 3) reduced VLDL apoB production; and 4) a delayed catabolism of a portion of Lp(a).—Ikewaki, K., W.
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