Abstract
The effects of diets enriched with cholesterol and different fats upon plasma lipoproteins and hepatic low density lipoprotein (LDL) receptor mRNA levels were studied in a group of 18 normal baboons. Animals were fed diets containing 1% cholesterol and 25% fat as either coconut oil, peanut oil, or olive oil for a period of 20 weeks. Plasma total cholesterol, high density lipoprotein (HDL) cholesterol, beta-lipoprotein (LDL + very low density lipoprotein) cholesterol, apolipoprotein B and apolipoprotein A-I were measured in samples obtained at 4-week intervals. All three diet groups demonstrated a statistically significant increase in plasma cholesterol as compared to base line throughout the experiment. Hepatic LDL receptor (LDL-R) mRNA levels were quantified by dot blot hybridization in serial liver biopsies. Animals fed saturated fat sustained a significant reduction in hepatic LDL-R mRNA as compared to those fed either monounsaturated or polyunsaturated fat. A strong negative correlation between LDL-R mRNA and plasma total cholesterol (r = -0.71), HDL cholesterol (r = -0.76), and plasma apo A-I (r = -0.77) was observed only in those animals fed coconut oil. Weak negative correlations between LDL-R mRNA and other plasma parameters did not achieve statistical significance. We conclude that saturated and unsaturated oils may influence plasma cholesterol levels in part through differential effects on LDL receptor biosynthesis in baboons.
Highlights
Our results show that the feeding of cholesterol and fat suppresses the level of hepatic LDL receptor mRNA in the baboon
Feeding of saturatedfat leads to a much greater decrement in hepatic LDL receptor mRNA than eithermonoor polyunsaturated fat. This is the first report that thedifferential effects of unsaturated fatty acid versw saturated fatty acid on lipoprotein metabolism maybe mediated through changes in expression of the hepatic gene coding for the LDL
The patternof response clearly demonstrates the negative influence of the diet containing saturated fat onthe level of LDL receptor mRNA in the liver, at least in five of six animals fed the coconut oil diet
Summary
High density lipoprotein; PAGE, polyacrylamide gel electrophoresis; Plasma Analyses-Venous blood was collected in 2.7 mM EDTA, SDS, sodium dodecyl sulfate. Samples of of whole plasma were heat-dissociated in SDS-PAGE sample buffer 20-100 mg of liver were homogenized in 0.75-1.0 ml of 10 mM Trisat a dilution of 1:20 and stored a t -80 "C for later analysis by SDS- HC1, pH 8.0,1mM EDTA, 0.02%sodium azide on ice with a motor. Samples containing the equivalent of0.3 p1of whole plasma were preparation obtained from normal baboon liver was included in all subjected t o SDS-PAGE through 12% polyacrylamide slab gels [30]. Gelswere electrophoretically transferred to RNA samples for dot blot were denatured with phosphate-buffered nitrocellulose filter membranes (Schleicher & Schuell BA85) by the glyoxal according to McMaster and Carmichael [47] as modified by method of Towbin et ai.
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