Radiolabeled cholesteryl ethers trace LDL cholesteryl esters but not HDL cholesteryl esters in the rat Original Research Article

The intravascular metabolism of cholesteryl [1-14C]oleoyl ester and [1,2-3H(N)]cholesteryl palmityl ether was compared in the rat, an animal species without plasma cholesteryl ester transfer activity (CETA). The tracers had identical plasma disappearance rates when they were incorporated into human or rat low density lipoproteins (LDL). Fractional catabolic rates (FCR) were 0.081 ± 0.014 h−1 and 0.080 ± 0.013 h−1 for human LDL ester and ether and 0.098 ± 0.007 h−1 and 0.101 ± 0.007 h−1 for rat LDL ester and ether, respectively. In contrast, the ether had plasma disappearance rates that were 24%–25% lower than the ester when they were incorporated into human or rat high density lipoproteins (HDL). FCR were 0.230 ± 0.020 and 0.173 ± 0.030 h−1 for human HDL ester and ether and 0.131 ± 0.020 h−1 and 0.100 ± 0.017 h−1 for rat HDL ester and ether respectively. Biological screening of the rat HDL preparations did not affect these differences. The results of these studies indicate that in the absence of plasma CETA, cholesteryl ethers can be used to trace LDL cholesteryl esters but not to trace HDL cholesteryl esters.