Mevinolin and colestipol stimulate receptor-mediated clearance of low density lipoprotein from plasma in familial hypercholeserolemia heterozygotes

Abstract

In subjects with heterozygous familial hypercholesterolemia (FH), a 50% deficiency of receptors for plasma low density lipoprotein (LDL) impairs the removal of LDL from plasma and produces hypercholesterolemia. In these patients mevinolin, an inhibitor of 3-hydroi[y-3-methylglutaryl-CoA reductase, blocks dldenternlsynthesis and lowers plasma LDL levels. To determine the mechanism for the LDL-kmcring effect, we administered 131 I-labeled LDL intravenously to six FH heterozygotes before and during treatment with mevinolin and calculated the apparent fractional catabolic rote (FCR) and synthetic rate for LDL. After mevinolin treatment, the mean plasma LDL-chnlesterol level dedined from 262 to 191 mg/dl (27% decrease), the mean FCR for 131 I-labeled LDL increased from 0.30 to 0.41 pools per day (37% increase), and the mean calculated synthetic rate for LDL-protein did not change significantly. In one FH heterozygote with an lieal bypass and in another who received colestipol, the addition of mevinolin caused, respectively, a 41% and 60% decrease in plasma LDL levels and a 60% and 100% increase in the FCR for plasma LDL. The contribution of receptor-dependent pathways to the FCR for plasma LDL was estimated in three FH heterozygotes by simultaneous measurements of the FCR for native 131 I-labeled LDL and 125 I-labeld glucosylated LDL, which does not bind to LDL receptors. Whereas the removal rate for native LDL increased after mevinolin treatment, the removal rate for glucosylated LDL did not change. The corrent data suggest that mevinolin alone or mevinolin plus bile acid depletion (i.e., ileal bypass or colestipol therapy) decreases plasma LDL levels primarily by raising the number of LDL receptors and, thus, enhancing the removal of LDL from plasma.