Abstract 21310: ApoCIII RX19 Mutation Lowers the Production of ApoCIII and Increases the Clearance of VLDL-TG

Abstract

The APOCIII R19X mutation (rs76353203), has been found in ~5% of the Lancaster Old Order Amish. It is a C ->T substitution at the 55th nucleotide in human aolipoprotein C-III mRNA that prevents translation of mature apoC-III protein. The mutation decreases apoC-III levels by ~50% and confers favorable lipid profiles and less coronary artery calcification, providing evidence that ApoC-III deficiency is cardioprotective. This conclusion is supported by recent data in Danish and U.S. cohorts showing a 40% reduction in myocardial infarction rates in people with this mutation. The mechanisms whereby apoc-III deficiency exerts its effects are not fully understood. The aim of this study was to describe the fractional clearance rates (FCR) and production rates (PR) of apoB containing lipoproteins, apoCIII, and very low density lipoprotein (VLDL) tryglyceride (TG) in five Amish sibling pairs (CT vs. CC) discordant for the APOC3 R19X mutation and matched for age and sex. Methods: Sib pairs completed a 24-hr stable isotope kinetic study using leucine and glycerol. Blood samples were collected over 24-hr period. We measured plasma lipids and apoCIII by Elisa. We determined the FCR and PR of VLDL apoB, apoCIII, and VLDL-TG. Results: The CT subjects had a 38% decrease in baseline TG levels compared to CC. ApoCIII levels were reduced by 42% in the CT vs. CC. We observed reductions in VLDL-Chol (49%), IDL-Chol (52%), VLDL-TG(44%), and IDL-TG(39%) in the CT when compared to CC. The changes in plasma levels were due to an increase in the VLDL apoB FCR (p = 0.001) without significant changes in production. VLDL-TG FCR increased by 76% in the CT when compared to CC (p=0.03). We observed no differences in post-heparin plasma levels of hepatic and lipoprotein lipase activity in the CT vs. CC. The plasma changes in apoCIII were due to and increased FCR in the CT compared to CC. Conclusions: Reductions in plasma TG levels in heterozygous apoC-III deficient individuals is due to enhanced FCRs of VLDL-apoB and VLDL-TG.