Effect of simvastatin therapy on paraoxonase activity and related lipoproteins in familial hypercholesterolemic patients

Human paraoxonase (PON1) is a calcium-dependent esterase closely associated with high density lipoprotein (HDL)-containing apolipoprotein AI (apoAI), which has been shown to confer antioxidant properties to HDL. PON1 has been recently implicated in the pathogenesis of atherosclerosis. Low PON1 activities have been found in familial hypercholesterolemia (FH) and diabetes mellitus. We have undertaken a study of the effect of the lipid-lowering drug simvastatin on serum PON1 activity (in relation to paraoxon and arylesterase activity), on apoAI-containing and apolipoprotein B (apoB)-containing lipoproteins, and on lipid peroxide concentrations in 64 (39 women and 25 men) unrelated FH patients. We have also analyzed the influence of the PON1-192 and PON1-55 genetic polymorphisms on the response of PON1 activity to simvastatin therapy. A venous blood sample for a baseline analysis and another after 4 months of simvastatin therapy at a dosage of 20 mg per day were taken. The major effect of simvastatin on lipid traits was to decrease serum cholesterol, low density lipoprotein (LDL) cholesterol, and lipid peroxide concentrations by 19.9%, 26.3%, and 37.3%, respectively. There was also a significant decrease in serum apoB, LDL apoB, and triglyceride concentrations (20.5%, 21.1%, and 15.6%, respectively). Conversely, simvastatin had no significant influence on very low density lipoprotein-lipid content, HDL cholesterol, apoAI concentrations, and lipoprotein AI and AI:AII particles. Remarkably, serum PON1 activity toward paraoxon significantly increased during treatment with simvastatin (168. 7+/-100.3 U/L before therapy versus 189.5+/-116.5 U/L after therapy, P:=0.005). Arylesterase activity displayed only a nonsignificant trend to increase after therapy. Whereas PON1 activity levels were significantly lower in FH patients before simvastatin therapy compared with those of 124 normolipidemic subjects (168.7+/-100.3 versus 207.6+/-125.2 U/L, respectively; P:<0.05), this difference disappeared after simvastatin therapy. After simvastatin therapy, a significantly negative correlation between PON1 activity and lipid peroxide concentration was observed (r=-0.35, P:=0.028). The latter also strongly correlated with LDL cholesterol concentration (r=0.64, P:<0.001). Serum PON1 activity levels were significantly lower in the low-activity PON1-192 QQ and PON1-55 M carriers than in R carriers and in LL carriers, respectively. No significant differences were found in the therapeutic response of PON1 activity between genotype groups (8.5% and 11.1% increase for QQ homozygous and R-carrier FH patients, respectively, and 12.7% and 9.5% increase for LL homozygotes and M carriers, respectively). We conclude that simvastatin may have important antioxidant properties through increasing serum PON1 activity, perhaps as a consequence of reducing oxidative stress, by a mechanism independent of apoAI-containing lipoprotein concentration and without the influence of PON1-192 and PON1-55 genetic polymorphisms. Further studies are clearly warranted to clarify the precise mechanism by which simvastatin therapy is associated with increased PON1 activity.     

GDF11逆转巨噬细胞胆固醇堆积的分子机制研究

目的 观察生长转化因子（GDF）11在巨噬细胞泡沫化中的作用并探讨其可能的分子机制。方法 以不同浓度氧化型低密度脂蛋白(oxLDL)处理RAW264.7细胞,将75 μg/ml oxLDL与不同浓度GDF11共处理过夜,采用荧光染色观察巨噬细胞脂质堆积情况。提取总蛋白或是总RNA,采用Western blot方法检测oxLDL对巨噬细胞GDF11表达的作用,采用实时荧光定量PCR检测GDF11、ABCA1、ABCG1、CD36、IL-1、IL-6及MMP9 mRNA的表达。结果 oxLDL可以显著诱导巨噬细胞胆固醇堆积并抑制巨噬细胞GDF11表达（P<0.05）,外源给予GDF11可以抑制oxLDL引起的巨噬细胞胆固醇堆积（P<0.05）;oxLDL孵育能够有效诱导CD36、IL-1、IL-6和MMP9 mRNA表达并抑制ABCA1、ABCG1 mRNA表达（P<0.05）,外源给予GDF11刺激可以有效逆转oxLDL对于CD36、IL-1、IL-6和MMP9 mRNA的诱导和对于ABCA1、ABCG1 mRNA的抑制（P<0.05）。结论 GDF11可以有效抑制巨噬细胞泡沫化进程,与其有效逆转oxLDL对于CD36、IL-1、IL-6和MMP9 mRNA的诱导和对于ABCA1、ABCG1 mRNA的抑制相关。     

Effects of high cholesterol high fat diet on plasma lipoproteins in familial hypercholesterolemia

Heterozygous individuals with familial hypercholesterolemia possess about half of the normal numbers of functioning receptors on their cells. This is thought to be responsible for their hypercholesterolemia. In normals, dietary cholesterol increases LDL production and decreases LDL receptor-related LDL clearance, resulting in elevations in LDL cholesterol levels of ～30 mg/dL. To assess the effects of high fat and high cholesterol diets on the lipoproteins of individuals with diminished LDL receptors, three kinds of diets, including ones high in cholesterol, were fed to four patients with familial hypercholesterolemia, in the expectation that diet effects on apoB- or apoE-containing lipoproteins would be exaggerated. The basal diet consisted of 15% protein, 30% fat, 55% carbohydrate, 300 mg/d cholesterol, $\text{P}\text{S}$ ratio 0.4; the high fat diet was identical except that fat calories were 55% and carbohydrate 30%; the high fat-high cholesterol diet was identical with the high fat diet except ～750 or ～1,500 mg/d of cholesterol were added. Each diet was eaten for five weeks at home and for the sixth week at the general Clinical Research Center. Fasting (12–14 hours) plasmas were collected every two weeks for lipoprotein-lipid and apoprotein quantitation. At the end of each period, fasting and 4-hour postprandial samples were analyzed also by zonal ultracentrifugation and gel permeation chromatography. The significant results were as follows: (1) on analysis of fasting samples on the fat + Chol diet, measures of the levels of VLDL (ie, VLDL lipids, VLDL protein on zonal ultracentrifugation, VLDL-associated lipids, and apoE on chromatography) fell; measures of LDL were not consistently changed; and measures of HDL₂ and HDL_c rose. Compositions of VLDL were altered, ie, mass % of triglycerides fell and cholesterol rose. Zonal effluent profiles of VLDL, LDL, HDL₂, and HDL₃ were not altered, nor were gel chromatographic elution patterns of cholesterol, triglycerides, apoB, apoA-I, and apoE, suggesting that the sizes and/or densities of lipoproteins were not altered. Therefore, the numbers of VLDL particles must have fallen and the numbers of HDL₂ and HDL_c must have risen. The nature and magnitude of the changes fell within the range of changes previously observed in normolipidemic subjects. The data indicate that having diminished numbers of LDL receptors did not affect the abilities of these patients to resist diet-induced qualitative or quantitative alterations of their plasma lipoproteins. Clearly other adaptive mechanisms can compensate for the diminished numbers of LDL receptors.     

Diurnal changes in plasma lipoproteins in normal subjects and diabetics

Summary Significant diurnal variations in levels of total plasma cholesterol, HDL cholesterol and LDL cholesterol were found in the majority of 12 normals, 13 maturity onset and 14 insulin requiring diabetics. The variations in total cholesterol and its lipoprotein subfraction were more marked in diabetics. These variations were not correlated in either diabetic group with glucose control as assessed by the level of glycosylated haemoglobin. The significance of the diurnal changes in total plasma cholesterol and the lipoprotein subfractions in relation to arteriovascular disease is discussed.     

Effect of wy-14,643 on cholesterol metabolism in normal and hypercholesterolemic rats

Studies with the rat have shown Wy-14,643, [4-chloro-6-(2,3-xylidino)-2pyrimidinylthio]-acetic acid, to be a highly potent antihypercholesterolemic agent with an activity approximately 60 times that of clofibrate. Drug administration resulted in a reversible hepatomegalia in normal and hypercholesterolemic rats. Liver. enlargement was accompanied by an increase in the absolute amount of cholesterol but the concentration was unchanged in the normal rat and reduced in the hypercholesterolemic rat. Seven days of Wy-14,643 administration to normal and hypercholesterolemic rats that had initially received a tracer dose of [4-¹⁴C] cholesterol resulted in an accumulation of cholesterol radioactivity in the liver accompanied by a decreased fecal excretion of sterols and bile salt radioactivity.

The biosynthesis of liver lipid from [1-¹⁴C]acetate was markedly accelerated by the drug but the liver cholesterol radioactivity was similar to that of the controls indicating that the increased amount of cholesterol in the liver of the treated rats had been transported preformed.

After 47 days of drug administration cessation of dosing resulted in a massive increase in serum cholesterol. The results of these experiments indicate that the hypocholesterolemic action of Wy-14,643 is not the result of a decreased intestinal absorption or of an increase in cholesterol catabolism but involves a retention of cholesterol in the liver and probably other tissues possibly through an inhibition of cholesterol transport mechanisms.     

Effects of probucol on plasma lipids and lipoproteins in familial hypercholesterolemic patients with and without apolipoprotein E4

It has been reported that total cholesterol (Chol) response to probucol is greater in familial hypercholesterolemic (FH) patients with apo E4 than in those without apo E4. We further examined the effect of probucol on plasma triglyceride (TG) and lipoprotein-Chol levels as well as total Chol levels in heterozygous FH patients with apo E4 (n = 14 for apo E4/3, n = 1 for apo E4/4) and without apo E4 (n = 31 for apo E3/3). Probucol was administered in a dosage of 500 mg twice daily for 3 months. The reduction in total Chol levels was significantly greater in FH patients with apo E4 (-90 mg/dl, -27.5%) than in those without apo E4 (-41 mg/dl, -13.7%). The reduction in low density lipoprotein (LDL)-Chol levels was also significantly greater in FH patients with apo E4 (-73 mg/dl vs. -34 mg/dl). There was a significant difference in the change in TG and very low density lipoprotein (VLDL)-Chol levels with treatment between the FH patients with apo E4 (-37 and -8 mg/dl, respectively) and without apo E4 (+8 and +2 mg/dl, respectively). However, there was no significant difference in the reduction in HDL-Chol levels between the 2 groups (-9 mg/dl vs. -9 mg/dl). It is concluded that FH patients with apo E4 showed the greater reduction in plasma TG levels as well as total Chol levels with probucol treatment than those without apo E4, and that the greater reduction in total Chol levels in them, as reported previously, was mainly due to the greater reduction in LDL-Chol levels and slightly due to that in VLDL-Chol levels.     

Laboratory-based assessment of plasma lipids and lipoproteins for the classification of familial hypercholesterolemic and hypertriglyceridemic states

Laboratory-based coronary heart disease risk assessment classically involves measurement of lipids and lipoproteins. In this review, information is provided on the methods commonly used in laboratories for the diagnosis of hyperlipidemia, including aspects of precision and accuracy. The latter, when fulfilled, allows the use of uniform reference values. Special attention is paid to the risk estimation using apolipoprotein B and lipoprotein(a) measurement. The overall aim of this review is to simplify the laboratory-based risk estimation for coronary heart disease and to provide help in interpreting the results for effective prevention and treatment of this complex disease.     

Lipoproteins and plasma cholesterol esterification in normal and diabetic subjects

Serum lipoproteins, separated by preparative ultracentrifugation and the activity of the plasma enzyme lecithin: cholesterol acyltransferase (LCAT) have been measured in insulin-dependent diabetics, non-insulin-dependent diabetics and in age-matched non-diabetic controls. In the insulin-dependent diabetics, mean total serum cholesterol and high density lipoprotein cholesterol (HDL-C) concentrations were significantly higher than in controls. Non-insulin-dependent diabetics had significantly raised total triglycerides and cholesterol, but HDL-C levels were essentially normal. The increased low density lipoprotein cholesterol (LDL-C) in both diabetic groups was statistically significant in men. A methodological study of HDL separation techniques was carried out to facilitate interpretation of these findings. Mean LCAT activity, by a method reflecting combined enzyme and substrate effects was significantly increased in these diabetic groups. The results confirm recent reports of a raised HDL-C in those insulin-dependent diabetics who are prone to coronary heart disease.     

Effect of fenofibrate on serum lipoproteins in subjects with familial hypercholesterolemia and combined hyperlipidemia

The effects on serum lipoproteins were studied in 8 patients with familial heterozygous hypercholesterolemia and 9 patients with familial combined hyperlipidemia during an 8-week treatment with fenofibrate. VLDL, IDL, LDL and HDL were isolated by ultracentrifugation and precipitation. Lipids and apolipoproteins A-I and B were determined by enzymatic and immunonephelometric techniques, respectively. In hypercholesterolemia, administration of fenofibrate resulted in decreases of VLDL, IDL, and LDL (cholesterol -58.3%, -28.6%, and -24.4%), while, in combined hyperlipidemia, treatment with the drug lowered VLDL and IDL (-33.3% and -42.9%). HDL cholesterol and apolipoprotein A-I increased only in hypercholesterolemia (+22.9% and +6.9%).     

Effects of soy protein and casein in low cholesterol diets on plasma lipoproteins in normolipidemic subjects

Dietary plant proteins may lower plasma cholesterol and LDL concentrations in hypercholesterolemic patients when substituted for animal proteins, particularly in diets with low cholesterol and saturated fat content. Plant protein diets appear, however, to be without effect on plasma lipoprotein levels in normal subjects. In the present study, we have examined whether the origin of the dietary protein, i.e. plant (soy) or animal (casein), affects the plasma lipoproteins in normolipidemic subjects when these proteins are presented as components of diets low in cholesterol and saturated fat. The study followed a crossover design. Five men and 5 women consumed liquid formula diets containing 20% of calories as casein or soy protein, 28% as fat (mainly monounsaturated), and 52% as carbohydrate; the intake of cholesterol was less than 100 mg per day. The two dietary periods, each of 1 month duration, were separated by an interim period of 1 month on self-chosen food. Following an initial 30% reduction of cholesterol and LDL plasma levels on both diets, the concentrations of each of the major lipoprotein classes (VLDL, IDL, LDL, HDL2 and HDL3) were similar during the two experimental dietary periods. Body weights were essentially constant. Dietary soy protein and casein could not be distinguished in their effects on the plasma concentrations and chemical composition of the major lipoprotein classes in normolipidemic subjects.     

Enhanced in vitro oxidation of plasma lipoproteins derived from hypercholesterolemic patients.

In vitro oxidation of plasma lipoproteins, derived from either normolipidemic or hypercholesterolemic subjects, was performed in the presence of copper ions. Following this procedure, hypercholesterolemic low-density lipoprotein (LDL), very-low-density lipoprotein (VLDL), and high-density lipoprotein (HDL) demonstrated greater propensity for oxidation than the corresponding normocholesterolemic lipoproteins. The oxidation was determined by the concentration of thiobarbituric acid-reactive substances (TBARS), which was 44%, 71%, and 54% greater in the patients' VLDL, LDL, and HDL in comparison to the normocholesterolemic lipoproteins, respectively. An associated reduction in trinitrobenzensulfonic acid (TNBS) reactivity in the patients' lipoproteins was noted. These changes were consistent whether expressed per lipoprotein protein or per concentration. Macrophage cholesterol esterification induced by oxidized LDL was substantially increased (up to 59%) when patients' lipoproteins were used, in comparison to control lipoproteins. A positive correlation was present between the LDL cholesterol to protein ratio, the extent of lipoprotein oxidation, and macrophage uptake of the oxidized lipoproteins. The lipoprotein content of pro-oxidant and antioxidant constituents was also analyzed. No measurable ferric or copper ions could be found in association with any of the lipoproteins. However, arachidonic acid content of the patients' LDL was 10.1% +/- 1.0% in comparison to 6.2% +/- 0.8% of total lipoprotein fatty acids in the control group (n = 5). Antioxidants such as vitamin E and carotenoids were significantly reduced in all patients' lipoproteins compared with those of controls. Thus, we suggest that increased cholesterol and arachidonic acid content and reduced concentration of antioxidants in lipoproteins of hypercholesterolemic patients may be responsible for the enhanced propensity for oxidation observed in these lipoproteins.     

Phytosterols in milk as a depressor of plasma cholesterol levels: experimental evidence with hypercholesterolemic Portuguese subjects

Plant sterols have been reported to decrease plasma concentrations of cholesterol without any side effects. To evaluate the effects on plasma cholesterol concentrations and the hemorheological parameters, we performed a study with hypercholesterolemic patients (n = 19) treated with phytosterol-enriched milk (2 g/day). Hypercholesterolemic patients (n = 15) of matched age drinking equal type of milk but without phytosterols were used as control group. Concentrations of total cholesterol, HDL-C, LDL-C and hemorheological parameters were measured in the beginning, after 15 and 30 days of milk intake. After 15 days of beverage intake, hypercholesterolemic subjects treated with phytosterol-enriched milk showed a significant decrease in plasma concentrations of total cholesterol and LDL-C by 9.62% (p < 0.05) and 12.20% (p < 0.05), respectively. After 30 days, a little increase in the total cholesterol and LDL-C concentrations were observed. In the hypercholesterolemic control group there were nonsignificant changes between plasma concentrations of total cholesterol, HDL-C and LDL-C during the study. The evaluation of plasma viscosity and erythrocyte aggregation shows no changes statistically significant during the study for both groups studied. The results obtained during the study show a positive effect with the phytosterol-enriched milk as plasma cholesterol-lowering as combined treatment for hypercholesterolemia.     

Effect of dietary supplementation with glucomannan on plasma total cholesterol and low density lipoprotein cholesterol in hypercholesterolemic children

AIM: This paper evaluates the effect of the adjunct of the hydrosoluble fiber glucomannan to a Step-One-Diet in 40 plasma hypercholesterolemic children, during a randomized controlled trial, to reduce plasma cholesterol. METHODS: All the subjects recruited underwent an 8-week run in diet period; a Step-One-Diet was prescribed. After that, they were randomly allocated to one of two groups: Step-One-Diet only (control), and Step-One-Diet plus glucomannan in gelatine capsules. After another 8 weeks of treatment, the results were compared within and between the two groups. RESULTS: Glucomannan treated group showed decreased values in plasma total cholesterol (TC) and low density lipoprotein cholesterol (LDL-C) vs. control group after 8 weeks of treatment. The percentage decrease showed a statistically significant difference between sex groups. Decreases were observed in favor of female vs. male children in TC (24% vs. 9%) and LDL-C (30% vs. 9%). CONCLUSIONS: These results suggest that glucomannan may represent a rationale adjunct to diet therapy in primary prevention in high risk hypercholesterolemic children.     

Release of cholesterol from cell membranes to postprandial plasma from mildly hypercholesterolemic subjects: the effect of meals rich in olive and safflower oils

Triglyceride-rich lipoproteins increase net transport of cell cholesterol to postprandial plasma from healthy subjects after a meal rich in fat and cholesterol. The aim of the present study was to determine the effect of meals rich in polyunsaturated fats (PUFA) and monounsaturated fats (MUFA) and low in cholesterol on net in vitro transport of cholesterol from red blood cells (RBCs) to postprandial plasma from 21 men with mild to moderate hypercholesterolemia in a randomized, crossover trial. Cholesterol concentration increased by 12% due to accumulation of cell cholesterol in fasted hypercholesterolemic plasma incubated with a 2/1 (vol/vol) excess of RBCs at 37 degrees C for 18 hours. The increase in cell cholesterol in plasma was mainly localized in the low-density lipoprotein (LDL) fraction (64%) and the remainder was approximately equally divided between the very-low-density lipoprotein (VLDL) and high-density lipoprotein (HDL) fractions. Accumulation of cell cholesterol in the LDL fraction prevented the significant decrease in LDL cholesterol in plasma incubated alone. When RBCs were incubated with postprandial plasma isolated 4 hours and 6 hours after liquid meals rich in safflower and olive oils, the accumulation of cell cholesterol in plasma increased significantly (11%, P <.004) above values for fasted plasma and irrespective of the type of fat in the meal. Also, the content of cell cholesterol increased significantly (70%, P <.001) in triglyceride (TG)-rich lipoproteins and decreased significantly (P =.006) in the LDL fraction, which remained the main ultimate destination of cell cholesterol in postprandial plasma. The increased loss of cell cholesterol to fasted and postprandial plasma was closely correlated (r > 0.823, P <.001) with the concomitant increase in plasma cholesteryl esters (CE) generated by lecithin cholesterol acyltransferase (LCAT) activity. There was a small (5%), significant (P <.001) increase in plasma cholesterol esterification in postprandial plasma. These data suggest that high-fat meals rich in MUFA and PUFA and low in cholesterol may produce a small postprandial increase in the capacity of plasma to accept cell membrane cholesterol that is limited by a concomitant small increase in plasma cholesterol esterification, in hypercholesterolemic subjects. Thus, low-fat, lipid-lowering diets may have a minimal effect on this capacity but will reduce levels of atherogenic LDL cholesterol that appear to be maintained by diffusion of cell cholesterol to plasma.     

Hydrophobic surfactant effects on aortic cholesterol accumulation and atherosclerosis in hypercholesterolemic rabbits

Studies were performed in hypercholesterolemic rabbits to determine whether the hydrophobic surfactant, Poloxalene 2930 (Pol), is of benefit under these conditions. Lipoprotein analyses plus chemical and morphologic studies of the aorta were performed to evaluate the results. In one study, rabbits were made hypercholesterolemic by dietary means and then divided into two groups and given a cholesterol-free diet with one group additionally given Pol with treatment continued for 10 weeks. Pol treatment resulted in less atherosclerosis but the mechanism for this effect was not apparent from lipoprotein analysis. In the other study 3 groups of rabbits were given a cholesterol-rich diet for 16 weeks. Two groups received Pol supplement with one of these groups receiving a dose that was too small to prevent hypercholesterolemia. In this group plus the group on diet alone comparable degrees of hypercholesterolemia were maintained throughout the study. Lipoprotein abnormalities were similar in these two groups except that those on Pol had a more normal cholesterol to apolipoprotein B ratio. The amount of atherosclerosis in both groups was mild but aortic cholesterol content was much less for the Pol group. It is concluded that Pol limits cholesterol accumulation in the aortic wall of hypercholesterolemic rabbits and can retard the development of atherosclerosis.     

Inhibition of cholesterol synthesis by atorvastatin in homozygous familial hypercholesterolaemia

Patients with homozygous familial hypercholesterolaemia (HoFH) have markedly elevated low density lipoprotein (LDL) cholesterol levels that are refractory to standard doses of lipid-lowering drug therapy. In the present study we evaluated the effect of atorvastatin on steady state concentrations of plasma lipids and mevalonic acid (MVA), as well as on 24-h urinary excretion of MVA in patients with well characterized HoFH. Thirty-five HoFH patients (18 males; 17 females) received 40 mg and then 80 mg atorvastatin/day. The dose of atorvastatin was increased further to 120 mg/day in 20 subjects and to 160 mg/day in 13 subjects who had not achieved LDL cholesterol goal, or in whom the dose of atorvastatin had not exceeded 2.5 mg/kg body wt per day. LDL cholesterol levels were reduced by 17% at the 40 mg/day and by 28% at the 80 mg/day dosage (P<0.01). Reduction in LDL cholesterol in the five receptor negative patients was similar to that achieved in the 30 patients with residual LDL receptor activity. Plasma MVA and 24-h urinary excretion of MVA, as markers of in vivo cholesterol synthesis, were elevated at baseline and decreased markedly with treatment. Urinary MVA excretion decreased by 57% at the 40 mg/day dose and by 63% at the 80 mg/day dosage (P<0.01). There was a correlation between reduction in LDL cholesterol and reduction in urinary MVA excretion; those patients with the highest basal levels of MVA excretion and thus the highest rates of cholesterol synthesis having the greatest reduction in LDL cholesterol (r=0.38; P=0.02). Increasing the dose of atorvastatin to 120 and 160 mg/day did not result in any further reduction in LDL cholesterol or urinary MVA excretion suggesting a plateau effect with no further inhibition of cholesterol synthesis at doses of atorvastatin greater than 80 mg/day.     

Stimulation of cholesterol and lipid synthesis by insulin in familial hypercholesterolemic fibroblasts

Cultured skin fibroblasts from two patients with homozygous familial hypercholesterolemia and three normal subjects were preincubated for 24 hours in medium containing 10% delipidated serum with insulin concentrations of 0.4, 4, or 40 ng/mL. [14C]acetate incorporation into total lipids, cholesterol, and phospholipids was significantly increased in familial hypercholesterolemic cells at insulin concentrations of 0.4 and 4 ng/mL, which had no effect in normal cells. When the data were normalized as percent stimulation over control for individual experiments, [14C]acetate incorporation into cholesterol was comparable at 40 ng/mL in both cell types. Similar results were obtained in cells preincubated in serum free artificial medium. Coordinate increases in the activity of 3-hydroxy-3-methylglutaryl CoA reductase in response to insulin were not found. These studies show that familial hypercholesterolemic cells have an altered lipogenic response to low concentrations of insulin.     

Adrenal cholesterol uptake from plasma lipoproteins: regulation by corticotropin.

The transfer of lipoprotein-bound cholesterol into adrenal cells was examined. Adrenal glands from unstimulated or corticotropin stimulated hypophysectomized rats were incubated with high density lipoprotein (HDL) or low density lipoprotein LDL containing radiolabeled cholesterol. The rate of transfer of labeled cholesterol from HDL into the glands was two to three times greater than from LDL. Corticotropin stimulation increased the transfer of cholesterol from HDL but not LDL. The effects of corticotropin were not dependent on subsequent cholesterol utilization for steroidogenesis. The process of cholesterol transfer from HDL was linear with time over 2 hr at 37 degrees and greatly reduced at 4 degrees. In addition, the transfer process became saturated above an HDL cholesterol concentration of 900 mug/ml. About 25% of the labeled adrenal cholesterol arising from HDL was recovered within the mitochondria. The labeled cholesterol within isolated mitochondria could undergo mitochondrial conversion to pregnenolone. Finally, the delipidated HDL apolipoproteins, apoA-I and apoA-II, when added to incubations containing less than saturating concentrations of HDL, stimulated transfer of labeled cholesterol from HDL to adrenal cells. These studies suggest that rat adrenal tissue possesses an HDL specific hormonally-responsive mechanism for accumulating extracellular cholesterol and that apoA-I and apoA-II have a significant function in the uptake process.