LDL particle size and LDL and HDL cholesterol changes with dietary fat and cholesterol in healthy subjects

We have conducted a dietary trial in 54 men and 51 women with a wide range of fasting cholesterol values to examine the use of low density lipoprotein (LDL) particle size to predict the lipoprotein response to dietary fat and cholesterol. After a 2-week low fat period, subjects were given two liquid supplements in addition to their low fat diet for 3 weeks each, one containing 31-40 g of fat and 650-845 mg of cholesterol, the other fat free. LDL particle type was determined by 3-15% gradient gel electrophoresis. On multiple regression, LDL type was independently related to plasma triglyceride (P < 0.001), waist circumference (P < 0.01), and high density lipoprotein (HDL) (P < 0.001) accounting for 56% of the variance in LDL type in the whole group. Change in LDL cholesterol with dietary fat and cholesterol was unrelated to LDL particle size in either men or women. However, change in HDL cholesterol in men was strongly related to LDL particle type (r = -0.52, P = 0.001) and change in HDL2 cholesterol in women was related to LDL particle type (r = -0.40, P < 0.01). In conclusion, we are unable to confirm the finding that LDL particle type can predict changes in LDL cholesterol following changes in dietary fat intake. However, LDL particle type can independently predict changes in HDL cholesterol in men and accounts for 27% of the variance.     

Psyllium-enriched cereals lower blood total cholesterol and LDL cholesterol, but not HDL cholesterol, in hypercholesterolemic adults: results of a meta-analysis

We conducted a meta-analysis to determine the effect of consumption of psyllium-enriched cereal products on blood total cholesterol (TC), LDL cholesterol (LDL-C) and HDL cholesterol (HDL-C) levels and to estimate the magnitude of the effect among 404 adults with mild to moderate hypercholesterolemia (TC of 5.17-7.8 mmol/L) who consumed a low fat diet. Studies of psyllium cereals were identified by a computerized search of MEDLINE and Current Contents and by contacting United States-based food companies involved in psyllium research. Published and unpublished studies were reviewed by one author and considered eligible for inclusion in the meta-analysis if they were conducted in humans, were randomized, controlled experiments, and included a control group that ate cereal providing /=50 y) on blood lipids. The meta-analysis showed that subjects who consumed a psyllium cereal had lower TC and LDL-C concentrations [differences of 0.31 mmol/L (5%) and 0.35 mmol/L (9%), respectively] than subjects who ate a control cereal; HDL-C concentrations were unaffected in subjects eating psyllium cereal. There was no effect of sex, age or menopausal status on blood lipids. Results indicate that consuming a psyllium-enriched cereal as part of a low fat diet improves the blood lipid profile of hypercholesterolemic adults over that which can be achieved with a low fat diet alone.     

Correction of hypoalphalipoproteinemia in LDL receptor-deficient rabbits by lecithin:cholesterol acyltransferase

Familial hypercholesterolemia (FH), a disease caused by a variety of mutations in the low density lipoprotein receptor (LDLr) gene, leads not only to elevated LDL-cholesterol (C) concentrations but to reduced high density lipoprotein (HDL)-C and apolipoprotein (apo) A-I concentrations as well. The reductions in HDL-C and apoA-I are the consequence of the combined metabolic defects of increased apoA-I catabolism and decreased apoA-I synthesis. The present studies were designed to test the hypothesis that overexpression of human lecithin:cholesterol acyltransferase (hLCAT), a pivotal enzyme involved in HDL metabolism, in LDLr defective rabbits would increase HDL-C and apoA-I concentrations. Two groups of hLCAT transgenic rabbits were established: 1) hLCAT+/LDLr heterozygotes (LDLr+/-) and 2) hLCAT+/LDLr homozygotes (LDLr-/-). Data for hLCAT+ rabbits were compared to those of nontransgenic (hLCAT-) rabbits of the same LDLr status. In LDLr+/- rabbits, HDL-C and apoA-I concentrations (mg/dl), respectively, were significantly greater in hLCAT+ (62 +/- 8, 59 +/- 4) relative to hLCAT- rabbits (21 +/- 1, 26 +/- 2). This was, likewise, the case when hLCAT+/ LDLr-/- (27 +/- 2, 19 +/- 6) and hLCAT-/LDLr-/- (5 +/- 1, 6 +/- 2) rabbits were compared. Kinetic experiments demonstrated that the fractional catabolic rate (FCR, d(-1)) of apoA-I was substantially delayed in hLCAT+ (0.376 +/- 0.025) versus hLCAT- (0.588) LDLr+/- rabbits, as well as in hLCAT+ (0.666 +/- 0.033) versus hLCAT- (1.194 +/- 0.138) LDLr-/- rabbits. ApoA-I production rate (PR, mg x kg x d(-1)) was greater in both hLCAT+/LDLr+/- (10 +/- 2 vs. 6) and hLCAT+/LDLr-/- (9 +/- 1 vs. 4 +/- 1) rabbits. Significant correlations (P < 0.02) were observed between plasma LCAT activity and HDL-C (r = 0.857), apoA-I FCR (r = -0.774), and apoA-I PR (r = 0.771), while HDL-C correlated with both apoA-I FCR (-0.812) and PR (0.751). In summary, these data indicate that hLCAT overexpression in LDLr defective rabbits increases HDL-C and apoA-I concentrations by both decreasing apoA-I catabolism and increasing apoA-I synthesis, thus correcting the metabolic defects responsible for the hypoalphalipoproteinemia observed in LDLr deficiency.     

Minimally oxidized LDL is a potent inhibitor of lecithin:cholesterol acyltransferase activity

The oxidation of low density lipoproteins (LDL) has been implicated in the development of atherosclerosis. As a variety of highly reactive lipid peroxidation products can transfer from oxidized LDL to HDL, we evaluated the potential deleterious effects of LDL oxidation on HDL-cholesterol metabolism. To address this issue, we exposed the HDL-containing d > 1.063 g/ml fraction of human plasma to copperoxidized LDL and assessed lecithin:cholesterol acyltransferase (LCAT) activity and apolipoproteinA-I (apoA-I) structure. To determine whether LCAT was directly affected by oxidized LDL, independent of crosslinking of apoA-I, we used an exogenous, [14C]cholesterol-labeled proteoliposome substrate to measure plasma LCAT activity. We observed an inhibition of LCAT activity where copper-oxidized LDL possessing only 2.3 +/- 0.1 and 7.3 +/- 1.4 TBARS produced 24 +/- 3% and 47 +/- 10% reductions in [14C]cholesterol esterification by 1 h, respectively. Copper-oxidized LDL that had been passed through a GF-5 desalting column, while retaining only one-third of its original TBARS, possessed nearly all of its LCAT inhibitory capacity suggesting that the LCAT inhibitory factor(s) was a lipophilic oxidation product. Analysis of polarlipids isolated from copper-oxidized LDL indicated that phospholipid and sterol fractions effectively inhibited LCAT. Copper-oxidized LDL, with as little as 6.3 TBARS, also produced intermolecular crosslinking of apoA-I molecules. Taken together, these data suggest that products of LDL oxidation may adversely affect HDL-cholesterol metabolism by two separate mechanisms: 1) a direct inhibitory effect on LCAT activity and 2) through crosslinking of apoA-I. If occurring in vivo, minimally oxidized LDL may impair cholesteryl ester formation on HDL thereby limiting the ability of HDL to function efficiently in the putative antiatherogenic reverse cholesterol transport pathway.     

Regression of severe atherosclerotic plaque in patients with mild elevation of LDL cholesterol

BACKGROUND: Intensive risk factor reduction in patients with dyslipidemias and coronary atherosclerosis has been shown to result in alterations in coronary artery morphology and reduced clinical events. However, the impact of such interventions in populations with relatively normal levels of low-density lipoproteins (LDL) is unclear. METHODS: To test the hypothesis that intensive risk factor reduction results in angiographic regression in patients with only mildly elevated levels of LDL, 14 patients with angiographically proven coronary atherosclerosis were entered into the University of California Davis Coronary Artery Disease Regression Program and intensively treated with pharmacologic and nonpharmacologic interventions for 2 years. Quantitative angiography was performed prior to and after 2 years of therapy to determine changes in coronary artery diameter. RESULTS: As a result of this program, dietary fat intake was reduced by 58% and LDL fell from 120 +/- 7 mg/dL to 104 +/- 6 mg/dL (p = 0.05). The average diameter of the measured arterial locations (including all 53 stenoses and 292 nondiscrete regions) on study entry was 2.74 +/- 0.05 mm. After 24 months, there was a net increase in arterial diameter (regression) of +0.05 +/- 0.04 mm to 2.81 +/- 0.05 mm (p = 0.01). While there was no significant change in the average diameter of discrete stenoses, all 8 lesions > or = 50% initial diameter narrowing regressed, with a mean diameter change of + 0.2 mm. Conversely, only 1 of 8 mild lesions < or = 20% regressed, while 4 progressed. Intermediate lesions (20% to 50%, n = 37) had balanced progression and regression. CONCLUSIONS: When examined as a continuous variable, there was a significant linear correlation between initial lesion severity (% stenosis) and the extent of regression (mm). Therefore, risk factor reduction (dietary therapy, exercise, psycho-social counseling, and lipid lowering therapy) in patients with only mild dyslipidemia results in angiographic regression of more severe lesions (> 50% initial stenosis), but does not prevent progression of mild lesions (< 20%). These findings demonstrate that intensive risk factor reduction in patients with only mild elevation of lipids beneficially influences the morphology of the most severe lesions.     

Potential interaction of troglitazone and cyclosporine

BACKGROUND: Troglitazone (Rezulin) is a promising new oral hypoglycemic agent recently approved by the Federal Drug Administration for use in type II diabetes mellitus. Although troglitazone is not metabolized by the cytochrome p450 3A isozyme family, it is a potential inducer of this system. Other medications, e.g., rifampin and phenobarbital, which also induce p450 3A activity, have been reported to significantly decrease cyclosporine (CsA) concentrations. METHODS: We report a case of a stable renal transplant patient who had a decrease in CsA concentration after beginning troglitazone and who subsequently developed an acute rejection episode. We then reviewed all stable renal patients begun on troglitazone over the previous 6 months. RESULTS: The seven transplant patients who had been started on troglitazone therapy experienced a statistically and clinically significant decrease in CsA 12-hr trough levels immediately after the institution of troglitazone therapy. CONCLUSION: A potential interaction exists between troglitazone and CsA. Transplant patients on CsA who receive troglitazone therapy should be monitored closely.     

Lovastatin decreases de novo cholesterol synthesis and LDL Apo B-100 production rates in combined-hyperlipidemic males

The effect of lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, on the kinetics of de novo cholesterol synthesis and apolipoprotein (apo) B in very-low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), and low-density lipoprotein (LDL) was investigated in five male patients with combined hyperlipidemia. Subjects were counseled to follow a Step 2 diet and were treated with lovastatin and placebo in randomly assigned order for 6-week periods. At the end of each experimental period, subjects were given deuterium oxide orally and de novo cholesterol synthesis was assessed from deuterium incorporation into cholesterol and expressed as fractional synthesis rate (C-FSR) and production rate (C-PR). Simultaneously, the kinetics of VLDL, IDL, and LDL apo B-100 were studied in the fed state using a primed-constant infusion of deuterated leucine to measure fractional catabolic rates (FCR) and production rates (PR). Drug treatment resulted in significant decreases in total cholesterol (-29%), VLDL cholesterol (-40%), LDL cholesterol (-27%), and apo B (-16%) levels and increases in HDL cholesterol (+13%) and apolipoprotein (apo) A-I (+11%) levels. Associated with these plasma lipoprotein responses was a significant reduction in both de novo C-FSR (-40%; P = .04) and C-PR (-42%; P = .03). Treatment with lovastain in these patients had no significant effect on the FCR of apoB-100 in VLDL, IDL, or LDL, but resulted in a significant decrease in the PR of apoB-100 in IDL and LDL. Comparing the kinetic data of these patients with those of 10 normolipidemic control subjects indicates that lovastatin treatment normalized apoB-100 IDL and LDL PR. The results of these studies suggest that the declines in plasma lipid levels observed after treatment of combined hyperlipidemic patients with lovastatin are attributable to reductions in the C-FSR and C-PR of de novo cholesterol synthesis and the PR of apoB-100 containing lipoproteins. The decline in de novo cholesterol synthesis, rather than an increase in direct uptake of VLDL and IDL, may have contributed to the decline in the PR observed.     

Dietary cholesterol affects serum lipids, lipoproteins and LDL metabolism in cynomolgus monkeys in a dose-dependent manner

To examine the mechanism(s) underlying the cholesterolemic response to dietary cholesterol and saturated fatty acids, low density lipoprotein (LDL) metabolism was studied in two groups of cynomolgus monkeys fed diets containing 30 or 36% of total energy as fat. At each dietary fat level, the same group of monkeys was sequentially fed three dietary cholesterol concentrations as egg yolk in the following sequence: low (0.01 mg/kJ), medium (0.03 mg/kJ) and high (0.05 mg/kJ) for 30, 32 and 24 wk, respectively. Dietary polyunsaturated and monounsaturated fatty acids were the same in the two groups; the 6% difference in fat was due to the saturated fatty acids, 12:0 and 14:0. Serum total cholesterol, LDL cholesterol and LDL apolipoprotein B concentrations increased (P < 0.05) with dietary cholesterol in a dose-dependent manner in both fat groups. These elevations were the result of generally increasing LDL apolipoprotein B production rates, concomitant with reduced LDL apolipoprotein B fractional clearance at the high cholesterol intake. Serum HDL cholesterol and HDL apolipoprotein A-I concentrations were not affected in a consistent manner. These results demonstrate that cynomolgus monkeys are hyperresponsive to dietary cholesterol compared with humans, suggesting that this model may be useful in identifying metabolic and genetic predictors for hyperresponsiveness to dietary cholesterol in humans as well as assessing the metabolic heterogeneity of responses to dietary cholesterol.     

The rabbit 15-lipoxygenase preferentially oxygenates LDL cholesterol esters, and this reaction does not require vitamin E

The oxidation of low density lipoprotein (LDL) by mammalian 15-lipoxygenases (15-LOX) was implicated in early atherogenesis. We investigated the molecular mechanism of 15-LOX/LDL interaction and found that during short term incubations, LDL cholesterol esters are oxygenated preferentially by the enzyme. Even when the LDL particle was loaded with free linoleic acid, cholesteryl linoleate constituted the major LOX substrate. In contrast, only small amounts of free oxygenated fatty acid isomers were detected, and re-esterification of oxidized fatty acids into the LDL ester lipid fraction was ruled out. When LDL was depleted from alpha-tocopherol, specific oxygenation of the cholesterol esters was not prevented, and the product pattern was not altered. Similar results were obtained at low (LDL/LOX ratio of 1:1) and high LOX loading (LDL/LOX ratio of 1:10) of the LDL particle. During long term incubations (up to 24 h), a less specific product pattern was observed. However, when the hydroperoxy lipids formed by the 15-LOX were immediately reduced by the phospholipid hydroperoxide glutathione peroxidase, when the reaction was carried out with vitamin E-depleted LDL, or when the assay sample was diluted, the specific pattern of oxygenation products was retained over a long period of time. These data suggest that mammalian 15-LOX preferentially oxidize LDL cholesterol esters, forming a specific pattern of oxygenation products. During long term incubations, free radical-mediated secondary reactions, which lead to a more unspecific product pattern, may become increasingly important. These secondary reactions appear to be suppressed when the hydroperoxy lipids formed are immediately reduced, when alpha-tocopherol-depleted LDL was used, or when the incubation sample was diluted. It may be concluded that 15-LOX-initiated LDL oxidation constitutes a dual-type oxygenase reaction with an initial enzymatic and a subsequent nonenzymatic phase. The biological relevance of this dual-type reaction for atherogenesis will be discussed.     

Dietary soluble fiber lowers plasma LDL cholesterol concentrations by altering lipoprotein metabolism in female guinea pigs

This experiment was designed to evaluate the effects of pectin (PE), guar gum (GG) and psyllium (PSY) intake on VLDL and LDL metabolism in female guinea pigs fed high dietary cholesterol. Guinea pigs were fed a 15 g/100 g fat diet containing 0.25 g/100 g cholesterol with 12.5 g/100 g PE, 12.5 g/100 g GG, 7.5 g/100 g PSY or 12.5 g/100 g cellulose (control diet) for 4 wk. Plasma cholesterol concentrations were 29, 43 and 39% lower in guinea pigs fed PE, GG or PSY, respectively, compared with the control group (P < 0.0001). Plasma apolipoprotein (apo) B concentrations were 16-22% lower in the groups fed soluble fiber compared with the control group (P < 0.01). In contrast, hepatic cholesterol and triglyceride concentrations were not different among the PE, GG, PSY and control groups. No differences in triacylglycerol (TAG) or apo B secretion rates, measured by blocking VLDL catabolism by triton (WR 1339) injection, were observed, whereas plasma LDL apo B fractional catabolic rates (FCR), determined by injection of radiolabeled LDL, were higher in guinea pigs fed GG or PSY than in those from the control group. All sources of dietary soluble fiber reduced LDL apo B flux (P < 0.05). These results suggest that the mechanisms of plasma LDL cholesterol lowering by dietary soluble fiber are distinctive for each fiber source and result in specific alterations in lipoprotein metabolism in female guinea pigs. Differences between male and female guinea pigs in response to these diets are discussed.     

Association of a leucine(7)-to-proline(7) polymorphism in the signal peptide of neuropeptide Y with high serum cholesterol and LDL cholesterol levels

High serum levels of total and LDL cholesterol are important risk factors in the development of atherosclerotic coronary artery disease. Cholesterol metabolism is affected by nutritional, environmental and genetic factors. Neuropeptide Y (NPY), which is widely expressed in both the central and peripheral nervous systems, has an important role in the hypothalamic regulation of energy balance by stimulating food intake and favoring energy storage through increased lipoprotein lipase activity in white adipose tissue. As a part of ongoing study of the genetic basis of obesity, we screened the NPY gene for sequence variants. We report here the identification of a common Leu(7)-to-Pro(7) polymorphism in the signal peptide of NPY. Presence of this Pro(7) in NPY was associated with higher serum levels of total and LDL cholesterol in obese subjects participating in two independent Finnish and Dutch studies. Furthermore, normal-weight Finns with Pro(7) also had higher serum levels of total and LDL cholesterol than did subjects with Leu(7)/Leu(7), as analyzed in three subsequent determinations at 5-year intervals during a 10-year follow-up period. The NPY polymorphism was not associated with higher cholesterol levels in normal-weight Dutch. Our study provides evidence that NPY is linked to cholesterol metabolism and that the polymorphism producing Pro(7) in NPY is one of the strongest genetic factors identified thus far affecting serum cholesterol, particularly in obese subjects.     

Dietary isoflavones reduce plasma cholesterol and atherosclerosis in C57BL/6 mice but not LDL receptor-deficient mice

To assess the cardiovascular effects of systemically administered opioid agonists, changes in blood pressure and heart rate were observed after intravenous (i.v.) administration of U50,488H (trans-3,4-dichloro-N-[2-(1-pyrrolidinyl) cyclohexyl]benzeneacetamide), a selective kappa-opioid receptor agonist, and DAMGO (D-Ala2, N-Me-Phe4, Gly5-ol), a selective mu-opioid-receptor agonist. Intravenous administration of U50,488H (1.2 mg/kg) and DAMGO (0.3 mg/kg) to the awake sheep resulted in an immediate increase in blood pressure. The pressor response to U50,488H was accompanied by an increase in heart rate. In contrast, there was no accompanying change in heart rate in response to DAMGO. We hypothesized that the lack of a reflex bradycardia to the pressor responses of both the mu- and kappa-opioid-receptor agonists was due to a blunting of baroreflex-mediated bradycardia. The reflex bradycardia to norepinephrine (0.6 microg/kg/min) was significantly reduced in the presence of DAMGO but not U50,488H. In view of the lack of effect of U50,488H on the baroreflex, we further hypothesized that the tachycardia it elicited was due to an increase in sympathetic activity. Pretreatment with propranolol (0.1 mg/kg) completely blocked the tachycardia elicited by U50,488H. These data suggest that the lack of a reflex bradycardia to the pressor response of DAMGO is due to a blunting of baroreflex-mediated bradycardia. In contrast, the increase in heart rate caused by U50,488H is mediated by sympathetic activation of the heart.     

Coadministration of acetaminophen and troglitazone: pharmacokinetics and safety

Troglitazone, a PPAR-gamma agonist, enhances the actions of insulin on muscle and liver. It is metabolized predominantly in the liver to a sulfate conjugate and a quinone metabolite. Acetaminophen also undergoes metabolism by conjugation. This three-way crossover study in 12 healthy male volunteers was conducted to investigate the effects of acetaminophen on the metabolism of troglitazone and vice versa. No statistically or clinically relevant differences in area under the concentration-time curve extrapolated to infinity (AUCinfinity) were observed for troglitazone, its quinone metabolite, or acetaminophen. A statistically significant decrease in troglitazone sulfate conjugate during administration with acetaminophen was not clinically relevant. No statistically or clinically relevant differences were observed in maximum concentration (Cmax), time to Cmax (tmax), or elimination half-life of troglitazone, its two main metabolites, and acetaminophen or in acetaminophen urinary sulfate excretion, although there was a slight decrease in acetaminophen glucuronide excretion during administration with troglitazone. Adverse events were minor and similar between treatments. These findings suggest that troglitazone and acetaminophen can be coadministered without adverse clinical consequences.     

Hypocholesterolemic effect of lycopene and beta-carotene is related to suppression of cholesterol synthesis and augmentation of LDL receptor activity in macrophages

Beta-Carotene and lycopene are derived from plants, and they share similar initial synthetic pathway with cholesterol, which is synthesized in animal but not in plant cells. Thus, we sought to analyze the effect of carotenoids on macrophage cholesterol metabolism, in comparison to the effect of LDL cholesterol and of the cholesterol synthesis inhibitor, fluvastatin. In J-774 A. 1 macrophage cell line, the cellular cholesterol synthesis from [3H]-acetate, but not from [14C] mevalonate, was suppressed by 63% any by 73% following cell incubation with beta-carotene or lycopene (10 microM) respectively, in comparison to a 90% and 91% inhibition by LDL (100 micrograms of cholesterol), or by fluvastatin (10 micrograms/ml) respectively. However, unlike LDL derived cholesterol, which also suppresses macrophage LDL receptor activity, lycopene and beta-carotene augmented the activity of the macrophage LDL receptor, similarly to the effect of fluvasfatin. In agreement with these in vitro observations, dietary supplementation of tomato's lycopene (60 mg/day) to 6 males for a 3 months period resulted in a significant 14% reduction in their plasma LDL cholesterol concentrations. We thus conclude that dietary supplementation of carotenoids may act as moderate hypocholesterolemic agents, secondary to their inhibitory effect on macrophage 3-hydroxy-3-methyl glutaryl coenzyme A (HMGCoA) reductase, the rate limiting enzyme in cholesterol synthesis.     

Influence of anti-LDL receptor antibody on the transfer of cholesterol from LDL to isolated lymphocytes in normal subjects

Results 2 1/2 years after an enuresis nocturna training are presented, including rate of success, percentage and duration of relapse for 113 children (mean age 11.6 year at the start of the training). The bibliotherapeutic treatment by parents did not require any intervention by a professional. Behaviour of parents in the event of a relapse differed between training conditions. Children in the Arousal condition recovered faster from a relapse, 90% of their parents used the Arousal training again at relapse or did not intervene at all and none of them consulted a professional. Clearly they had confidence in the method of Arousal training: combining the alarm device with reinforcement for correct behaviour at the time the alarm goes off. Parents in control conditions did not use the alarm device as often as the parents in the Arousal condition, but tried other means with less success, including consulting professionals.