Synthesis and breakdown of Very Low Density Lipoprotein Apo‐B100 measured with stable isotope methodology

Abstract

Increased concentration of Very Low Density Lipoprotein (VLDL) is an important and common risk factor for cardiovascular disease. VLDL concentration depends on the balance between synthesis and degradation, which can be influenced by many drugs and nutrients. The present study was designed to establish novel methods to simultaneously measure the fractional synthesis and breakdown rates of VLDL Apo‐B100. Six elderly (2 males, 4 females; 66.7 ± 2.4 (SE) years; 72.4 ± 6.8 kg) completed a study with constant infusion of two different tracers of leucine. 2H3‐leucine was infused for nine hours, whereas 1‐13C‐leucine was infused only for the first four hours. VLDL was isolated from plasma by ultracentrifugation, and Apo‐B100 was precipitated from this fraction by isopropanol. Basal Apo‐B100 fractional synthetic rate (FSR) was calculated from the linear part of the plasma enrichment slope of 2H3‐leucine vs. the plateau part of the slope. The fractional breakdown rate (FBR) of Apo‐B100 was obtained from the decay curve of the 1‐13C‐leucine, corrected for the incorporation of label. The basal FSR of Apo‐B100 was 18.33 ± 0.66 %/hr, whereas the FBR of Apo‐B100 was 16.31 ± 0.71 %/hr. These results are in agreement with previous reported measurements of Apo‐B100 secretion rates using isotope methodologies, and indicate that both fractional Apo‐B100 synthesis and breakdown can be reliably and simultaneously measured using stable isotopes.P30 AG024832 NIH/NIA, Shriners grant 8490, M01 RR 00073.