Effects of treatment of hypertriglyceridaemia with gemfibrozil on serum lipoproteins and the transfer of cholesteryl ester from high density lipoproteins to low density lipoproteins.

Lipoprotein composition and cholesterol esterification, before and after treatment with gemfibrozil, have been examined in the fasting and postprandial state in nine patients with primary hypertriglyceridaemia who participated in a double-blind, placebo controlled study. After 8 weeks of treatment fasting serum triglycerides were reduced significantly from 6.05 mmol/l (range 2.48-10.99 mmol/l) to 1.76 mmol/l (range 1.16-11.90 mmol/l) (P less than 0.001). This was mainly due to a decrease in the triglyceride content of the Sf 12-20, 60-400 and Sf greater than 400 lipoprotein fractions (P less than 0.05). The Sf 0-12 fraction showed an increase in cholesteryl ester, free cholesterol, phospholipids and protein. Consistent with these findings there was a net increase in the mass concentration of the Sf 0-12 fraction (P less than 0.05) and a decrease in that of small very low density lipoproteins (Sf 20-60) (P less than 0.05). In the 8 patients in whom it was measured there was a 40% reduction in the rate at which cholesteryl esters derived from radiolabelled-free cholesterol appeared in very low density lipoprotein (VLDL) and low density lipoprotein (LDL) measured in an in vitro system (P less than 0.02), but serum lecithin:cholesterol acyl transferase (LCAT) activity was unchanged. At the end of each treatment phase (placebo or gemfibrozil) patients were given a mixed meal containing 100 g of fat. Treatment with gemfibrozil resulted in a reduction in serum triglyceride concentrations at all time points for at least 5 h after the meal (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of the stimulatory effect of pregnenolone-16 alpha-carbonitrile on biliary cholesterol output in the rat by manipulation of the rate of hepatic cholesterol synthesis

In female rats fed a plain ground diet containing pregnenolone-16 alpha-carbonitrile, biliary cholesterol output increased twofold, whereas bile acid and phospholipid output either remained unchanged or decreased slightly. There was a 32% increase in liver weight, a 3.5-fold increase in cholesteryl esters, and a 45% decrease in the rate of hepatic sterol synthesis. When pregnenolone-16 alpha-carbonitrile was fed with AOMA, an agent that blocks cholesterol absorption, there was less of an increase in cholesteryl esters, the inhibitory effect of pregnenolone-16 alpha-carbonitrile on hepatic sterol synthesis was abolished, and biliary cholesterol output was increased to an even greater extent. In contrast, when pregnenolone-16 alpha-carbonitrile was fed together with cholesterol, there was a 14-fold increase in the level of cholesteryl esters, an 85% decrease in the rate of hepatic sterol synthesis, and a marked reduction in biliary cholesterol output. The increase in biliary cholesterol saturation produced by either pregnenolone-16 alpha-carbonitrile alone or pregnenolone-16 alpha-carbonitrile with AOMA occurred with little or no change in plasma cholesterol levels and bile acid pool size. Because biliary cholesterol saturation in rats given pregnenolone-16 alpha-carbonitrile appears to correlate with the rate of hepatic cholesterol synthesis, the drug likely mediates its effect on biliary lipid composition at an intrahepatic level and may provide an important model for determining how overproduction of cholesterol by the body results in excessive transport of cholesterol into bile.     

Studies on aorta during development. II. Differences in ontogeny of the key enzymes involved in cholesteryl ester synthesis and hydrolysis in rabbit aorta

It is well known that cholesteryl ester accumulation is dramatically increased in the atherosclerotic artery. The enzymes acyl-CoA: cholesterol acyltransferase (ACAT), acid cholesteryl esterase (ACE) and neutral cholesteryl esterase (NCE) may play key roles in the accumulation of cholesteryl esters in the arterial wall. However, very little is known regarding the developmental pattern of the key enzymes involved in cholesteryl ester synthesis and hydrolysis. The total activities of ACAT, ACE and NCE were measured by radioassay using liposomal substrates in rabbit aortic homogenates. Our results indicate that ACAT activity decreases as a quadratic function with age (P less than 0.05). ACAT activity (pmol/100 mg protein/min) decreased from a high value in the fetus at term (63.3 +/- 7.4) to gradually lower values with increasing age. On the other hand, ACE activity (pmol/mg protein/min) was low in the fetus at term, and changed as a quadratic function with age (P less than 0.05) increasing gradually to higher activities with age up to a maximum at 12 weeks then decreased at 21 weeks. NCE activity (pmol/mg protein/min) increased dramatically from a low value in the fetus at term (3.34 +/- 0.48) to a maximum value at 1.5 weeks (14.65 +/- 2.73) then decreased as a linear function with increasing age up to 21 weeks (P less than 0.05). Plasma total cholesterol (mg/dl) also increased sharply from the fetal value at term of 98.5 +/- 5.2 to a maximum value at 1.5 weeks of 666.4 +/- 33.4, then decreased as a quadratic function with increasing age up to 21 weeks (40.8 +/- 6.7) (P less than 0.05). The free cholesterol content (microgram/mg protein) of the aortic tissue was initially high in the fetus (24.8 +/- 5.9) then increased with age. Examination of the ratio of synthesis to hydrolysis of cholesteryl esters as an index of enzyme activity units demonstrated a very high index in the fetus of 6.1 that rapidly decreased with increasing age in the young adult rabbit down to a value of 0.4 by 21 weeks of age. Correlation coefficients between enzyme activities, plasma cholesterol levels and aortic cholesterol levels indicated (a) a positive correlation of NCE activity with plasma cholesterol, (b) a negative correlation of NCE and ACE with aortic-cholesteryl ester content, and (c) no significant correlation of ACAT activity with either plasma cholesterol or aortic cholesterol content, indicating other factors are involved.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fatty acid composition of serum lipids in patients with a coronary bypass operation

The fatty acid composition of serum phospholipids and cholesteryl esters was analysed in 71 male patients with angiographically defined three-vessel coronary artery disease (CAD) selected for a coronary bypass operation. Their 71 control subjects were matched according to age, sex, smoking, relative weight, and absence of CAD. The concentrations of fatty acids, 14:0, 16:0 and 16:1 of the serum phospholipids, were significantly (P less than 0.01, P less than 0.05 and P less than 0.01, respectively) higher in CAD patients than in the controls. On the other hand, linoleic (18:2 omega 6), linolenic (18:3 omega 3) and arachidonic (20:4 omega 6) acids were at a significantly lower level in the patients when compared to the controls. The polyunsaturated/saturated fatty acids (P/S) ratio in serum phospholipids was significantly (P less than 0.01) lower in the patients than in the controls. In the cholesteryl ester fraction the results paralleled those of the phospholipids. Significant correlations were obtained between the polyunsaturated fatty acids and the high density lipoprotein cholesterol or apolipoprotein A-I in the control subjects but most of these correlations were absent in the patients. Our present results further support the importance of linoleic acid in the protection against atherosclerosis. However, no unequivocal evidence on the possible beneficial effect of long-chain omega 3-fatty acids in comparison with omega 6-acids was obtained.     

Arterial lipid biochemistry in the spontaneously hyperlipidemic Zucker rat and its similarity to early atherogenesis

In the present studies, arterial lipid metabolism was evaluated in the spontaneously hyperlipidemic obese Zucker rat (fa/fa), the lean Zucker rat (Fa/-), and the Sprague-Dawley (SD) rat. Mean serum cholesterol levels in the obese Zucker, lean Zucker and SD rats were 216 +/- 18 mg/dl, 145 +/- 14 mg/dl and 84 +/- 5 mg/dl, respectively. Arterial cholesterol content was in the same rank order as plasma cholesterol and ranged from a mean of 2.23 +/- 0.10 mg/gm wet wt. in the obese rats to 1.36 +/- 0.04 mg/gm wet wt. in the SD rats. The increased arterial sterol in the obese rats was associated with increased lipid metabolism activity. The in vitro incorporation of [14C]oleate into arterial cholesteryl esters was increased 3-4-fold (P less than 0.01) and incorporation into phospholipids and triglycerides was also elevated (P less than 0.001 and P less than 0.01, respectively). The arterial sterol content and arterial lipid metabolism pattern observed in obese Zucker rat aortas are similar to those found in vessels of other species undergoing atherogenic change.     

The effect of lovastatin treatment on low-density lipoprotein hydrated density distribution and composition in patients with intermittent claudication and primary hypercholesterolemia.

The effects of lovastatin treatment on density distribution and composition of low-density lipoproteins (LDL) were studied using a density gradient ultracentrifugation method in 35 hypercholesterolemic patients with severe peripheral vascular disease. Lovastatin caused a 32% mean reduction in LDL particle mass and a 36% reduction in LDL cholesterol. The cholesteryl ester to apolipoprotein (apo) B, free cholesterol to apo B, and phospholipid to apo B weight ratios in LDL decreased significantly during treatment (P less than .01, P less than .01, and P less than .001, respectively). The effect on plasma triglycerides (Tg) was not uniform. Plasma Tg levels decreased in 25 patients, but increased in 10 patients. Since plasma Tg level influences the LDL density distribution and composition, the patients were also subgrouped and analyzed according to change in plasma Tg. In those with increased plasma Tg, the light LDL particles were reduced more and the dense particles less compared with patients with decreased Tg. The mean Tg content of LDL increased (from 7.7% to 9.3%; P less than .05) and the weight ratio of core lipids (cholesteryl ester/Tg) in LDL decreased (from 4.57 to 3.44; P less than .01) in patients with increased plasma Tg during treatment. The results indicate that the change in plasma Tg (decrease or increase) determined the qualitative changes in LDL observed during lovastatin treatment.     

Plasma lipoproteins and lipolytic enzyme activities during endurance training in sedentary men: Changes in high-density lipoprotein subfractions and composition

Eighteen healthy sedentary males took part in supervised bicycle training for 50 minutes three to five times a week. Twelve subjects (group A) trained for 6 weeks at heavy intensity, and six subjects (group B) trained for 12 weeks at moderate intensity. Maximal oxygen uptake increased by about 20% (P less than 0.01). Body weight and composition as well as diet remained unchanged. After 6 weeks plasma high-density lipoprotein (HDL) cholesterol concentrations had increased by 7% (P less than 0.05) in all subjects. The increase was most marked in group B at 14% (P less than 0.05) compared to 3% in group A (ns). Apolipoprotein AI (apo AI) increased by about 7% in both groups (P less than 0.01). After 12 weeks HDL cholesterol and apo AI levels had almost returned to initial values. Measurements of HDL components showed increases of 6% to 12% in free cholesterol, cholesteryl ester (P less than 0.05), and phospholipid (P less than 0.01); whereas, the minor triglyceride fraction decreased by 20% (P less than 0.01). Zonal ultracentrifugation in four subjects revealed a preferential rise of about 35% in the HDL2 subfraction, increasing the HDL2/HDL3 ratio by about 20%. In parallel, the composition of the lipoprotein classes changed. The protein moiety of all classes, except low-density lipoprotein (LDL), expanded at the expense of the core components cholesteryl ester and triglyceride. Hepatic lipase (HL) activity decreased by 6% (P less than 0.05), and lipoprotein lipase (LPL) activity in adipose tissue increased by about 50% (P less than 0.05) during the first 6 weeks of training, while LPL activity in postheparin plasma and skeletal muscle did not change. The transient rise in HDL cholesterol levels was correlated (P less than 0.05) to the elevation of adipose tissue LPL activity. The alterations in HDL concentration were also related to changes in body composition and diet, especially to an increase in fat intake.     

The effect of bezafibrate on very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) composition in type 1 diabetes associated with hypercholesterolaemia or combined hyperlipidaemia.

Lipoprotein composition was examined in type 1 diabetic subjects with hypercholesterolaemia +/- hypertriglyceridaemia during a 3-month double-blind placebo controlled assessment of bezafibrate therapy. The predominant effect was on lipoprotein lipid content. In those with hypercholesterolaemia alone, bezafibrate significantly reduced the cholesterol (particularly esterified cholesterol) and triglyceride content of large very low density lipoprotein (VLDL) (Svedberg flotation units (Sf) 60-400) in comparison to the placebo group (P less than 0.05), and a trend towards a reduction in free and esterified cholesterol within the intermediate density lipoprotein fraction (IDL) (Sf 12-20) was noted. Low density lipoprotein (LDL) composition was unaltered and in general phospholipid and protein concentrations and cholesteryl ester/protein ratios within the lipoprotein fractions were unaffected. Large VLDL cholesterol and triglyceride concentrations in those with combined hyperlipidaemia were significantly decreased following bezafibrate therapy, both in comparison to placebo-treated subjects and to baseline concentrations (P less than 0.05). An additional significant reduction in small VLDL (Sf 20-60) free cholesterol was recorded (P less than 0.05). Average reductions of large and small VLDL protein of 50-56% were not significant because of wide variation in responses. Bezafibrate had no effect on the abnormal composition of IDL and LDL, characteristic of Type 1 diabetes, regardless of whether or not hypertriglyceridaemia was associated with hypercholesterolaemia. Its major action was to lower VLDL lipid concentrations, but it may also reduce the lipid content of intermediate density lipoprotein in Type 1 diabetes.     

The effect of abnormal plasma and cellular sterol content and composition on low density lipoprotein uptake and degradation by monocytes and lymphocytes in sitosterolemia with xanthomatosis

The hypothesis that abnormal low density lipoprotein (LDL) sterol content and composition in sitosterolemia with xanthomatosis affects LDL uptake and/or degradation was tested. Monocytes and lymphocytes from three patients and 12 age- and sex-matched controls were incubated at 37 degrees C in lipid-free medium with 125I-labeled LDL prepared from sitosterolemic patients (LDLs) and controls (LDLn) in the presence or absence of excess unlabeled lipoproteins. Normal monocytes and lymphocytes took up and degraded LDLs 13% to 30% less than LDLn (P less than .05). Sitosterolemic monocytes and lymphocytes degraded LDLn 13% and LDLs 67% more actively than control cells (P less than .05). Sitosterolemic monocytes contained three times more sterols and stanols than controls (P less than .01), of which 12% were plant sterols and 2% were 5 alpha-saturated stanols. In one patient, stimulating bile acid synthesis by ileal bypass surgery reduced plasma and monocyte sterol and stanol concentrations about 60%, and was associated with a 40% to 50% increase in LDLn and LDLs receptor-mediated degradation. The decreased uptake and degradation of LDLs relative to LDLn by normal cells suggest that abnormal plant sterols in LDLs may reduce its affinity for the native LDL receptor. Increased receptor-mediated uptake and degradation of LDLs by sitosterolemic cells in the presence of high cellular sterol content may result from failure of the sitosterolemic cells to down-regulate LDL receptor synthesis. Ileal bypass surgery increased cellular LDL receptor activity, reduced plasma and cellular sterol concentrations, and may diminish the risk of premature atherosclerosis in sitosterolemia.     

Dietary plant stanol esters reduce VLDL cholesterol secretion and bile saturation in apolipoprotein E*3-Leiden transgenic mice

Dietary plant stanols lower serum cholesterol levels in humans and in hyperlipidemic rodents, mainly by inhibition of the intestinal cholesterol absorption. We used female apolipoprotein E*3-Leiden transgenic mice to investigate the consequences of this effect on serum lipid levels and hepatic lipid metabolism. Five groups of 6 or 7 mice received for 9 weeks a diet containing 0.25% cholesterol and 0.0%, 0.25%, 0.5%, 0.75%, or 1.0% (wt/wt) plant stanols (sitostanol 88% [wt/wt], campestanol 10% [wt/wt]) esterified to fatty acids. Compared with the control diet, plant stanol ester treatment dose-dependently reduced serum cholesterol levels by 10% to 33% (P<0.05), mainly in very low density lipoproteins (VLDLs), intermediate density lipoproteins, and low density lipoproteins. Furthermore, 1.0% of the dietary plant stanols significantly decreased the liver contents of cholesteryl esters (-62%), free cholesterol (-31%), and triglycerides (-38%) but did not change the hepatic VLDL-triglyceride and VLDL-apolipoprotein B production rates. However, plant stanol ester feeding significantly decreased the amounts of cholesteryl esters and free cholesterol incorporated in nascent VLDLs by 72% and 30%, respectively, resulting in a net 2-fold decreased VLDL cholesterol output. Liver mRNA levels of low density lipoprotein receptors, 3-hydroxy-3-methylglutaryl coenzyme A synthase, cholesterol 7alpha-hydroxylase, and sterol 27-hydroxylase were not changed by plant stanol ester feeding. Nevertheless, the serum lathosterol-to-cholesterol ratio was significantly increased by 23%, indicating that dietary plant stanol esters increased whole-body cholesterol synthesis. Plant stanol esters also significantly decreased the cholesterol saturation index in bile by 55%. In conclusion, in apolipoprotein E*3-Leiden transgenic mice, plant stanol ester feeding dose-dependently lowered serum cholesterol levels as a result of a reduced secretion of VLDL cholesterol. This was caused by a decreased hepatic cholesterol content that also resulted in a lowered biliary cholesterol output, indicative of a reduced lithogenicity of bile in these mice.     

Insulin-like growth factor type I (somatomedin-C) stimulates high density lipoprotein (HDL) metabolism and HDL-supported progesterone biosynthesis by swine granulosa cells in vitro

Type I insulin-like growth factor (IGF-I) stimulated high density lipoprotein (HDL)-promoted progesterone production by swine granulosa cells cultured under serum-free conditions in vitro. In the presence of pure human IGF-I (50 ng/ml), the half-maximally effective concentration of swine HDL was 16 micrograms/ml (67% confidence limits; 15-17 micrograms/ml) after 2 days of exposure to this growth factor, 5.4 (2.6-9.8) micrograms/ml after 4 days, and 3.8 (1.2-4.8) micrograms/ml after 6 days. Maximal progesterone production increased approximately 10-fold in the presence of IGF-I and HDL on day 2, 125-fold on day 4, and 330-fold on day 6. The facilitative action of IGF-I on HDL-supported progesterone biosynthesis was accompanied by time-dependent stimulatory effects of IGF-I on trypsin-releasable HDL, trypsin-resistant cell-associated HDL, and degraded HDL (P less than 0.01). Moreover, incubation of swine granulosa cells with [3H]cholesteryl oleate-labeled HDL demonstrated that IGF-I exerted a time-dependent stimulatory effect on [3H]free cholesterol and [3H]cholesteryl ester accumulation in granulosa cells, and significantly augmented the secretion of [3H]progesterone (separated by two-dimensional TLC). In addition to the ability of IGF-I to amplify the cellular acquisition of radiolabeled sterol, this growth factor also increased the total mass of cellular cholesteryl ester and total cellular cholesterol as measured by microfluorometric assay (P less than 0.01). We conclude that IGF-I facilitates the effective delivery of HDL-derived sterol substrate into the steroidogenic pool of ovarian cells. Such observations offer an additional role for the differentiative actions of this somatomedin in the expression of full steroidogenic potential by granulosa-luteal cells.     

Fatty acid composition in serum lipids and adipose tissue in severe obesity before and after six weeks of weight loss

Fatty acid composition was studied in 25 grossly obese patients (mean weight 116 +/- 21 (s.d.) kg) before and after 6 weeks of treatment with a combined program consisting of diet, behavioral modification and light exercise. Data were compared with results from nonobese controls. In obese patients the most marked differences were reduced relative contents of linoleic acid in serum triglycerides (P less than 0.001), cholesterol esters (P less than 0.05) and phospholipids (P less than 0.001). Linolenic acid was reduced in serum triglycerides (P less than 0.001) and in cholesterol esters (P less than 0.01). There were reciprocal increases in palmitic and palmitoleic acid (P less than 0.05) in these two serum lipid fractions. In adipose tissue of obese patients only minor differences were found in palmitoleic acid, which was increased, and in the saturated fatty acids with 14, 16 and 18 carbon atoms which were decreased. Weight loss (600 kcal/day for 6 weeks, P/S ratio about 0.5) did not affect adipose tissue fatty acid composition, but resulted in reductions of linoleic acid content in cholesterol esters and phospholipids, with reciprocal increases of palmitic and arachidonic acid in these fractions. Our results suggest that obese patients have low essential fatty acids content in their circulating plasma lipids already in a weight stable phase. Therefore it may be argued that in the development of long-term dietary restriction programs attention should be paid to the quality of the dietary fat.     

Abnormalities of composition and of in vitro lipolysis products of human small very low density lipoproteins in hypertriglyceridemia

Small (Sf 20-100) very low density lipoprotein (VLDL) particles were prepared by density gradient ultracentrifugation of plasma from normolipidemic and type IV hypertriglyceridemic post-infarction patients and healthy controls. The small VLDL separated from the plasma of severely hypertriglyceridemic post-infarction patients were found to contain twice the amount of cholesteryl esters per particle, compared with small VLDL from normolipidemic patients and healthy controls. There was a linear increase in the percentage of cholesterol that was esterified in the small VLDL with the serum VLDL triglyceride concentration (r = 0.66). When incubated for two hours with bovine lipoprotein lipase in excess and bovine albumin as a free fatty acid acceptor at one and the same triglyceride concentration in the medium, the end-product isolated by ultracentrifugation varied as a function of the serum VLDL triglyceride level. The amount of glyceride-glycerol recovered after two hours of incubation with lipoprotein lipase was 13.3 +/- 1.3% (mean +/- SEM) of the initial values and did not correlate with the VLDL triglyceride level. With rising serum VLDL triglyceride concentration, the product isolated in the low density lipoprotein (LDL) density region (1.006 less than d less than 1.063 kg/l) contained more total cholesterol and phospholipids. The linear correlation coefficients for these relations were 0.65 and 0.58 for cholesterol and phospholipids respectively. The ratio of total cholesterol to insoluble protein in the LDL density range after lipolysis rose with increasing serum VLDL triglyceride level (r = 0.68). The end-product was further characterized by density gradient ultracentrifugation of the incubate. In vitro LDL derived by lipolysis of normolipidemic small VLDL was denser than in vitro LDL of hypertriglyceridemic small VLDL. A significant relation was found between the percentage of cholesteryl esters of total cholesterol in the substrate and the relative amount of total cholesterol recovered in the LDL density fraction after lipolysis (r = 0.69). We suggest that the enrichment with cholesteryl esters of small VLDL from type IV hypertriglyceridemic patients is caused by lipid transfer from LDL and high density lipoprotein (HDL) and that the change in VLDL particle composition influences the precursor-product relationship to LDL.     

Hepatic stores of retinol and retinyl esters in elderly people

Post-mortem concentrations of hepatic retinol and retinyl esters were determined in 40 subjects aged over 65 years to assess the effects of disease and malnutrition on vitamin A reserves. Three groups of patients (mean age 79.6 years) were studied: (1) previously healthy, (2) chronically ill, (3) chronically ill and wasted. There was no significant difference in height or age between the groups, but group 3 was lighter than both group 1 (P less than 0.001) and group 2 (P less than 0.05). Free retinol and retinyl esters were measured by high pressure liquid chromatography, and the total hepatic retinol calculated. Analysis of variance showed that the three groups differed significantly (P less than 0.02) with regard to total retinol, retinyl palmitate and total retinyl ester content.     

Quantitation of plasma free cholesterol and cholesteryl esters by high performance liquid chromatography. Study of a normal population

We describe a convenient method for the separation and quantitation of plasma free cholesterol and cholesteryl esters by high performance liquid chromatography (HPLC). After extraction of 100 microliters plasma with isopropanol the plasma cholesteryl esters were resolved on a Zorbax ODS reversed-phase column by isocratic elution with acetonitrile/isopropanol (50:50, v/v). Baseline separation of the plasma cholesteryl esters including the internal standard was obtained within a 25-min run. The intra- and interassay CV was less than 4%. The results obtained by HPLC show good agreement with enzymatic and gas-liquid chromatographic methods. High performance liquid chromatography provides a simple method for the quantitation of individual cholesteryl esters avoiding tedious chromatographic and derivatisation steps inherent to GLC. Our HPLC method was applied to the monitoring of plasma cholesteryl esters in a normal population and can also be used for the study of cholesteryl esters from lipid extracts of biological samples.     

Plasma cholesterol esterification and transfer, the menopause, and hormone replacement therapy in women.

With the onset of the menopause, plasma lipids and lipoprotein metabolism changes toward a more atherogenic profile that is improved by HRT. To determine whether cholesterol esterification rate (CER) and transfer of cholesteryl esters from high density lipoproteins to apolipoprotein B-containing lipoproteins are affected by menopause and HRT, plasma newly synthesized cholesteryl ester transfer (NCET) activity, CER and plasma lipids, lipoproteins, and apolipoprotein concentrations were measured in perimenopausal women (age range: 40-55 yr), including 49 premenopausal women and 32 postmenopausal women who were subsequently randomized to receive either placebo or 17-beta estradiol/norethisterone for 6 months. Plasma NCET (P = 0.03) and CER (P = 0.008) were significantly higher in postmenopausal women. Plasma low density lipoprotein cholesterol concentration, high density lipoprotein concentration, and body mass index were independent predictors of plasma NCET in premenopausal women, and plasma triglyceride and apolipoprotein B concentrations were corresponding predictors in postmenopausal women. When data were adjusted for plasma triglyceride, plasma NCET activity was no longer significantly different (P = 0.81) between premenopausal and postmenopausal women. Plasma NCET and CER did not change significantly in postmenopausal women during HRT. These data suggest that the determinants of plasma NCET activity after menopause and increased levels of triglyceride-rich lipoprotein acceptors of cholesteryl esters may lead to increased plasma NCET that is not reduced by HRT in postmenopausal women.     

Metabolism of high density lipoproteins reconstituted with [3H]cholesteryl ester and [14C]cholesterol in the rat, with special reference to the ovary

In order to study the metabolism of high density lipoprotein (HDL)-carried sterol in the rat, human HDL was reconstituted with [14C]cholesterol and [3H]cholesteryl ester. After iv injection into immature PMSG-human CG primed rats pretreated with 4-aminopyrazolopyrimidine and aminoglutethimide, there was time-dependent accumulation of 3H and 14C in various organs which reached a maximum by 15-90 min. On a milligram wet weight basis, uptake of 3H and 14C was greatest in the adrenals, next in ovaries, followed by the liver, with little uptake by kidneys and spleen. On an organ basis, accumulation was greatest by the liver. At 15-45 min post injection, 60% of the 3H in the ovary was in free sterol, indicating hydrolysis of the accumulated cholesteryl esters, whereas 95% of the 3H in serum remained in sterol esters associated with HDL. Coadministration of excess unlabeled HDL, but not human low density lipoprotein, reduced accumulation of radioactivity by the ovaries and adrenals by 60%, indicating a specific and saturable uptake process. Granulosa cells cultured in lipoprotein-deficient medium with reconstituted HDL formed 3H- and 14C-labeled 20 alpha-hydroxypregn-4-en-3-one. Over a 24-h period, utilization of both [14C]cholesterol and [3H]cholesteryl ester was linear, but rates of utilization of the two sterol moieties were not parallel. There was preferential uptake and utilization of free sterol. A dose-response study demonstrated a Michaelis-Menten constant (Km) of 40-60 micrograms sterol/ml for both free and esterified cholesterol. Lysosomotropic agents (chloroquine and NH4Cl) had no effect on utilization of either free or esterified cholesterol for steroidogenesis but reduced degradation of 125I-labeled low density lipoprotein apoprotein. These findings lend further support to the concept of a distinct HDL pathway in steroidogenic cells of the rat, which involves 1) preferential uptake and utilization of free cholesterol from HDL and 2) does not require lysosomal activity.     

The amount of dietary cholesterol changes the mode of effects of (n-3) polyunsaturated fatty acid on lipoprotein cholesterol in hamsters

This study was designed to investigate the effects of the interaction between dietary (n-3) polyunsaturated fatty acids (PUFA) and different dietary cholesterol content on plasma and liver cholesterol in hamsters. Male Syrian hamsters consumed diets containing an incremental increase in dietary cholesterol content (0, 0.025, 0.05, 0.1 and 0.2%, w/w) with either (n-3) PUFA (21 g/100 g fatty acids) or (n-6) PUFA (37.4 g/100 g fatty acids) fat for 6 weeks. In hamsters fed the nonatherogenic diet (0 or 0.025% dietary cholesterol), very low density lipoprotein (VLDL)-cholesterol levels in the (n-3) PUFA group were not significantly different from those in the (n-6) PUFA group, and low density lipoprotein (LDL)-cholesterol levels in the (n-3) PUFA group were significantly lower than those in the (n-6) PUFA group. In contrast, in hamsters fed the atherogenic diet (0.1 or 0.2% dietary cholesterol), VLDL- and LDL-cholesterol levels in the (n-3) PUFA group were significantly higher than those in the (n-6) PUFA group, in a dose-dependent manner. When the hamsters were fed with 0, 0.025, 0.05, 0.1 or 0.2% (w/w) dietary cholesterol, high density lipoprotein (HDL) cholesterol concentration was significantly lower in the (n-3) PUFA group than those in the (n-6) PUFA group. Hepatic cholesteryl esters were significantly lower, while hepatic microsomal acyl-coenzyme A:cholesterol acyltransferase activity and VLDL-cholesteryl esters were significantly higher in hamsters fed (n-3) PUFA with the atherogenic diet (0.1 or 0.2% dietary cholesterol) than in those fed (n-6) PUFA with the atherogenic diet. Our results demonstrate that the amount of dietary cholesterol is an important factor in determining the mode and extent of effects of dietary (n-3) PUFA, especially on VLDL- and LDL-cholesterol levels. When dietary cholesterol intake was above 0.1% (w/w), the plasma cholesterol-lowering effect of (n-3) PUFA disappeared, and instead, it showed a cholesterol-increasing effect. However, the effects of dietary (n-3) PUFA on HDL-cholesterol are independent of dietary cholesterol content.     

Interaction of very-low-density lipoprotein isolated from type I (insulin-dependent) diabetic subjects with human monocyte-derived macrophages

Very-low-density lipoproteins (VLDL) (density less than 1.006 g/mL) were isolated from type I (insulin-dependent) diabetic patients in good to fair glycemic control and from age-, sex-, and race-matched, nondiabetic, control subjects. VLDL were incubated with human, monocyte-derived macrophages obtained from nondiabetic donors, and the rates of cellular cholesteryl ester synthesis and cholesterol accumulation were determined. VLDL isolated from diabetic patients stimulated significantly more cholesteryl ester synthesis than did VLDL isolated from control subjects (4.04 +/- 1.01 v 1.99 +/- 0.39 nmol 14C-cholesteryl oleate synthesized/mg cell protein/20 h; mean +/- SEM, P less than .05). The stimulation of cholesteryl ester synthesis in macrophages incubated with VLDL isolated from diabetic patients was paralleled by a significant increase in intracellular cholesteryl ester accumulation (P less than .05). The increase in cholesteryl ester synthesis and accumulation in macrophages were mediated by a significant increase in the receptor mediated, high affinity degradation (2.55 +/- 0.23 v 2.12 +/- 0.20 micrograms degraded/mg cell protein/20 h) and accumulation (283 +/- 35 v 242 +/- 33 ng/mg cell protein/20 h) of 125I-VLDL isolated from diabetic patients compared with VLDL from control subjects. To determine if changes in VLDL apoprotein composition were responsible for the observed changes in cellular rates of cholesteryl ester synthesis and accumulation, we also examined the apoprotein composition of the VLDL from both groups. There were no significant differences between the apoproteins B, E, and C content of VLDL from both groups. We also determined the chemical composition of VLDL isolated from both groups of subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Accumulation of cholesteryl esters and triglycerides in cultured macrophages incubated with plasma very low density lipoproteins from rats fed on casein or soybean protein diets containing moderate levels of cholesterol

Even when administered at a comparatively low level, dietary cholesterol produces significant changes in the properties of plasma lipoproteins in rats, particularly the d less than or equal to 1.006 g/ml fraction (VLDL). The occurrence of these changes is promoted by dietary casein. To test the hypothesis that these dietary-induced perturbations might include properties influencing lipoprotein-cell interactions of relevance to atherogenesis, cultured mouse peritoneal macrophages were incubated with VLDL isolated from male rats fed on diets containing either 0, 0.25 or 0.5% cholesterol with casein or soybean protein, respectively, as the sole source of protein. No increase in cholesteryl ester content, and a comparatively small rise in triglyceride content, was observed in macrophages incubated with VLDL from rats fed on cholesterol-free diets. In contrast, a significant and apparently saturable cellular accumulation of cholesteryl esters as well as triglycerides was produced by VLDL from cholesterol-fed rats. The curves showing cellular lipid accumulation versus VLDL-protein (or VLDL-cholesterol) content in the cell medium indicated different cellular affinity for VLDL from casein-fed rats in comparison with VLDL from soybean protein-fed rats. The apoprotein composition of VLDL differed between groups of rats fed on different types of dietary protein with higher proportions of apo C's in the casein-fed rats. In addition, cholesterol feeding resulted in increased proportions of apo A-I and apo A-IV in the plasma VLDL fraction.