Apolipoprotein E metabolism in normolipoproteinemic human subjects

Area of Science:

• Biochemistry
• Genetics
• Metabolic Research

Background:

• Human apolipoprotein E (apoE) exists in three common isoforms: apoE-2, apoE-3, and apoE-4.
• These isoforms are determined by three alleles (epsilon 2, epsilon 3, and epsilon 4) inherited co-dominantly.
• ApoE-3 is the predominant isoform in normolipidemic individuals, with epsilon 3 considered the normal allele.

Purpose of the Study:

• To investigate the metabolism of apolipoprotein E-3 (apoE-3) in normolipidemic subjects homozygous for the epsilon 3 allele.
• To determine the plasma concentration, residence time, and production rate of apoE-3.
• To compare apoE-3 metabolism between males and females and its catabolism relative to other apolipoproteins.

Main Methods:

• Kinetic analysis of apoE-3 metabolism in nine normolipidemic subjects.
• Measurement of plasma apoE-3 concentration, residence time, and production rate.
• Comparison of apoE-3 catabolism across different lipoprotein subfractions (VLDL, HDL) and with other apolipoproteins.

Main Results:

• In subjects homozygous for epsilon 3, plasma apoE-3 concentration was 4.8 mg/dl, residence time was 0.73 days, and production rate was 3.4 mg/kg-day.
• Males exhibited a shorter residence time and higher production rate of apoE-3 compared to females.
• ApoE-3 catabolism was faster than most studied apolipoproteins, with rapid clearance from VLDL and slower clearance from HDL.

Conclusions:

• ApoE-3 plays a significant role in the catabolism of triglyceride-rich lipoproteins.
• High-density lipoprotein (HDL) likely serves as a reservoir for apoE, facilitating its reassociation with newly secreted triglyceride-rich lipoproteins.
• The findings support the importance of apoE in lipoprotein metabolism and lipid transport.