Dietary fat-mediated changes in hepatic apoprotein [formula omitted] receptor in the guinea pig: Effect of polyunsaturated, monounsaturated, and saturated fat

Abstract

These studies investigated the effects of dietary fat quality on guinea pig plasma total and low-density lipoprotein (LDL) cholesterol and triglyceride levels; LDL composition, density, and binding affinity to hepatic apolipoprotein (apo) B E receptors; and hepatic apo B E receptor levels. Animals were fed semi-synthetic diets containing 7.5% (weight per weight) fat—either corn oil (CO), olive oil (OL), or lard. Plasma cholesterol levels were significantly lower on the CO diet compared with the OL and lard diets. The isolated LDL had mean peak densities that ranged from 1.071 for LDL from lard-fed animals to 1.075 for LDL from CO- and OL-fed animals. The cholesterol ester to protein ratio of the LDL particle decreased in CO-fed guinea pigs. Binding studies showed that these compositional changes of the LDL had no effect on the binding affinity of the particles to a standardized hepatic membrane preparation. Membrane phospholipid fatty acid compositions were significantly different among the three dietary fat groups. When hepatic membranes were incubated with 125I-labeled LDL, the receptor-mediated binding of LDL to membranes from CO-fed animals increased 1.5-fold compared with binding to membranes from OL- and lard-fed guinea pigs. Scatchard plots indicated an increase of 50% in receptor number in membranes of animals fed the CO diet, whereas the affinity of the hepatic apo B E receptor for LDL (K d) was virtually identical for all membranes. It is concluded from these data that the increase in specific binding observed in hepatic membranes from CO-fed guinea pigs is caused by an increased number of LDL receptors and not an increased affinity for the LDL particle.