Abstract
The hyperlipidemia associated with aging was characterized in the rat by comparing the plasma lipid, lipoprotein, and apolipoprotein profiles of adult (12 weeks old) and old (96 weeks old) male rats. Compared with those of the adult rats, the VLDL concentrations of the old rats were reduced, but IDL, LDL, and HDL concentrations were elevated. Despite a reduced VLDL concentration, concentrations of triglycerides in the plasma of the old rats were elevated. This phenomenon was attributed to an enrichment of triglyceride in the other lipoprotein fractions. In the old rats, hypercholesterolemia was the result of elevated IDL- and HDL-cholesterol whereas elevated plasma concentrations of apolipoproteins B and E were attributed to elevated LDL and HDL concentrations, respectively. Although concentrations of apolipoproteins A-I and A-IV did not change significantly in the plasma of the old rats, the distribution pattern of the apoA-IV was altered dramatically. Compared with the adult rats, a shift of apoA-IV in the HDL to the "lipoprotein-free" fraction was observed in the old rats, as measured by agarose gel chromatography. The data demonstrate that the hyperlipidemia in the old rats is associated with selective changes in the apolipoprotein profile.
Highlights
These changes are consistent with the changes in total protein of the lipoprotein fractions, i.e., very low density lipoproteins (VLDL)-protein decreased (8.1 mg/dl to 5.7 mg/dl) whereas intermediate density lipoproteins (IDL), low density lipoproteins (LDL), and high density lipoproteins (HDL)-protein increased with age (0.2mg/dl to 0.7 mg/dl; 5.9 mg/dl to 9.1 mg/dl; and 54.9 mg/ dl to 65.6 mg/dl, respectively)
Because we found higher apoB concentrations in old rats, we further separated apoB by using 3.5% polyacrylamide gels to see whether the contentsof high or low molecular weights forms of apoB differed in the old rat
In this study we showed that the marked hyperlipidemia of old rats is associated with selective changes in the concentrations of the plasma lipoproteins, and in the distributions of the lipids and the apolipoproteins within the lipoprotein classes
Summary
Insofar as the total plasma apoA-I concentration did not change statisticallywith age, the accumulation of apoA-I in the d > 1.210 g/ml fraction was greater in the old rat (Fig. 2C). Similar to the ultracentrifugation data, apoB concentrations were greater in old rats throughout theelution profiles for this apolipoprotein (Fig. 3A).
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