Characterization of the serum lipoproteins and their apoproteins in hypercholesterolaemic guinea pigs

Abstract

Hypercholesterolemia was induced in male guinea pigs after 6 days on a chow diet supplemented with 1.6% (wt/wt) cholesterol and 15% (wt/wt) corn oil. Both the VLD (very-low-density) and LD (low-density) lipoproteins were increased in cholesterol-fed animals, although the low concentrations of HD (high-density) lipoproteins remained essentially unchanged. LD lipoproteins of d [density] 1.019-1.100 were the major class, accounting for 74% of the total substances of d < 1.100. Both VLD and LD lipoproteins exhibited alterations in their chemical composition, physical properties and apolipoprotein content. The VLD lipoproteins in cholesterolemic animals were rich in cholesterol (25.9%), deficient in protein (4.9%) and exhibited electrophoretic mobility > that of .beta.-globulin; their average particle size (64.5 nm) was larger than that in controls (46.3 nm). The LD lipoproteins in animals fed on the experimental diet were also richer in cholesterol (53.1%) and of larger diameter (24.3 nm) than in the control group (41.1%) and 21.4 nm, respectively). The apolipoprotein-B content of VLD and LD lipoproteins was elevated in cholesterolemic animals, particularly in the VLD class, where it represented 74.8% of the total protein moiety. Apo-VLD lipoprotein exhibited an increase from 6-19% in its complement of tetramethylurea-soluble apolipoproteins with low electrophoretic mobility (relative mobility < 0.29); this was primarily accounted for by apolipoproteins characterized by high arginine (7.2 and 6.4%, respectively) and glutamic acid (20.1 and 20.0%, respectively) contents. There was little change in the soluble apolipoproteins Of LD lipoproteins in hypercholesterolemic animals. These studies showed the response of the guinea pig to dietary fat and cholesterol to be distinct from that elicited by similar stimuli in the rabbit, rat, pig and dog.