Individual variation in the effects of dietary cholesterol on plasma lipoproteins and cellular cholesterol homeostasis in man. Studies of low density lipoprotein receptor activity and 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in blood mononuclear cells

Abstract

The effects of dietary cholesterol on plasma lipoproteins and cholesterol homeostasis in blood mononuclear cells have been examined in healthy adults. Addition of 1,500 mg of cholesterol to the daily diet of 37 subjects for 14 d was associated with a wide range of response of plasma total cholesterol concentration (from -6 to +75 mg/dl; mean change, +29 mg/dl; P < 0.001). Increases in plasma cholesterol reflected increased cholesterol concentrations in intermediate density lipoprotein (IDL; 1.006-1.019 g/ml), low density lipoprotein (LDL; 1.019-1.063 g/ml), and the HDL(2) subclass (1.063-1.125 g/ml) of high density lipoprotein, which on average accounted for 20, 58, and 22%, respectively, of the total increment. Similar responses occurred in 14 other subjects given 750 mg cholesterol per day for 28 d. Plasma apolipoprotein B concentrations in IDL and LDL also increased. THESE EFFECTS ON PLASMA LIPOPROTEINS WERE ACCOMPANIED BY THREE CHANGES IN FRESHLY ISOLATED BLOOD MONONUCLEAR CELLS: (a) an increase in cell cholesterol content (mean change, +17%; P < 0.01); (b) suppression of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase activity (-32%; P < 0.001); and (c) reduction of LDL receptor activity (-74%; P < 0.01), quantified as the rate of degradation of (125)I-LDL to noniodide trichloroacetic acid-soluble material. These results provide the first direct evidence for the modulation of LDL receptor activity and HMG CoA reductase activity in a peripheral cell type in response to a dietary perturbation of human lipoprotein metabolism.The percentage increase in LDL cholesterol was negatively correlated with the percentage decrease in HMG CoA reductase activity (r = -0.49, P < 0.01). An additional negative correlation existed between the increment in plasma cholesterol concentration and the capacity of cells to degrade (125)I-LDL after derepression by preincubation for 72 h in lipoprotein-deficient medium (r = -0.74, P < 0.001). Thus, differences between individuals in the responses of the plasma lipoproteins to dietary cholesterol appear to be related in part to differences in the capacity of peripheral cells to catabolize LDL and to down-regulate cholesterol synthesis.