Alcohol and Hepatic Synthesis of Serum Apolipoproteins

Lin, Renee

Abstract

Studies have shown that moderate consumption of alcohol causes elevation of high density lipoprotein cholesterol (HDL-C). How alcohol affects either cholesterol or the protein moieties (apolipoproteins) of HDL remains unknown. We hypothesize that alcohol consumption increases hepatic synthesis, and alters hepatic secretion and degradation of HDL. Changes in these rates are dependent on the amount and duration of alcohol consumed. Transient increase in plasma lipids that have been observed by many investigators may be due to interplay of these processes.
Specific aims of this research plan are: (1) to examine changes of plasma lipids and apolipoproteins during the course of alcohol consumption at high, moderate and low dosage; (2) to study hepatic synthesis, secretion and uptake of apolipoproteins in cultured hepatocytes isolated from rats consuming various alcohol levels for a period of seven weeks; (3) to determine if an increase in hepatic synthesis of apolipoproteins by alcohol occurs at the pre- or post-translational level. Rats will be fed AIN'76 liquid diet containing different levels of alcohol. In some experiments, rats will be given the ethanol liquid diet by continuous intragastric infusion to produce more severe liver disease than fatty liver, i.e. hepatitis and fibrosis. Control rats will be paired fed or infused the same liquid diet but substitution ethanol isocalorically with maltose dextrin. Blood samples will be taken weekly to assay for serum lipids and apolipoproteins by enzyme immunosorbent assay (ELISA). Hepatocytes of control and alcohol-fed rats will be isolated and cultured as monolayers in serum-free Waymouth medium. the culture medium will be collected after 16 h and assayed for apolipoproteins by ELISA. In some experiments, 14C-leucine will be added to the culture medium and its rate of incorporation into medium and cellular apolipoproteins will be measured. Hepatic uptake of apolipoproteins will be studied by adding serum lipoproteins labelled with 125I-apolipoproteins to the culture medium. Changes in hepatic apolipoprotein mRNA's will be examined by in vitro translation using a rabbit reticulocyte lysate system as well as by c-DNA probe hybridization experiments. The experiments proposed here should provide new information on the effect of alcohol on hepatic synthesis of HDL and the mechanisms leading to hypercholesterolemia caused by alcohol consumption.