The effects of hypercholesterolaemia, simvastatin and dietary fat on the low density lipoprotein receptor of unstimulated mononuclear cells.

The in vivo expression and regulation of the LDL receptor of circulating mononuclear cells was studied using a sensitive spectrophotometric assay with low density lipoproteins conjugated to colloidal gold (LDL-gold). The high plasma cholesterol of familial hypercholesterolemic subjects was shown to be related to a low in vivo LDL receptor activity; cells from a homozygote had virtually no activity and those from 24 heterozygotes expressed 45% of the activity of cells from 35 normals. The average receptor activity of cells from 18 polygenic hypercholesterolemic (PH) subjects was not significantly different from normal but a low expression may have been a factor in six of these subjects. Simvastatin increased the LDL receptor activity of cells from the PH subjects by 70% while lowering their plasma cholesterol by 26%, but reducing the fat intake from 38% to 20% of energy and cholesterol from 239 to 96 mg/day had no effect on the receptor despite a 10% reduction in plasma cholesterol. Upregulation of the LDL receptor may therefore have been involved in the lowering of plasma cholesterol by simvastatin but not by the reduction in dietary fat and cholesterol.