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

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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-hydroxy-3-methylglutaryl-CoA reductase, blocks cholesterol synthesis and lowers plasma LDL levels. To determine the mechanism for the LDL-lowering effect, 131I-labeled LDL was administered i.v. to 6 FH heterozygotes before and during treatment with mevinolin and the apparent fractional catabolic rate (FCR) and synthetic rate for LDL were calculated. After mevinolin treatment, the mean plasma LDL-cholesterol level declined from 262 to 191 mg/dl (27% decrease), the mean FCR for 131I-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 1 FH heterozygote with an ileal 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 FH heterozygotes by simultaneous measurements of the FCR for native 131I-labeled LDL and 125I-labeled 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. Mevinolin alone or mevinolin plus bile acid depletion (ie., ileal bypass or colestipol therapy) apparently decreases plasma LDL levels primarily by raising the number of LDL receptors and, thus, enhancing the removal of LDL from plasma.
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