Aerobic Exercise Improves Reverse Cholesterol Transport in Cholesteryl Ester Transfer Protein Transgenic Mice

We analyzed the effect of a 6-week aerobic exercise training program on the in vivo macrophage reverse cholesterol transport (RCT) in human cholesteryl ester transfer protein (CETP) transgenic (CETP-tg) mice. Male CETP-tg mice were randomly assigned to a sedentary group or a carefully supervised exercise training group (treadmill 15 m/min, 30 min sessions, five sessions per week). The levels of plasma lipids were determined by enzymatic methods, and the lipoprotein profile was determined by fast protein liquid chromatography (FPLC). CETP activity was determined by measuring the transfer rate of ¹⁴C-cholesterol from HDL to apo-B containing lipoproteins, using plasma from CETP-tg mice as a source of CETP. The reverse cholesterol transport was determined in vivo by measuring the [³H]-cholesterol recovery in plasma and feces (24 and 48 h) and in the liver (48 h) following a peritoneal injection of [³H]-cholesterol labeled J774-macrophages into both sedentary and exercise trained mice. The protein levels of liver receptors were determined by immunoblot, and the mRNA levels for liver enzymes were measured using RT-PCR. Exercise training did not significantly affect the levels of plasma lipids or CETP activity. The HDL fraction assessed by FPLC was higher in exercise-trained compared to sedentary mice. In comparison to the sedentary group, a greater recovery of [³H]-cholesterol from the injected macrophages was found in the plasma, liver and feces of exercise-trained animals. The latter occurred even with a reduction in the liver CYP7A1 mRNA level in exercised trained animals. Exercise training increased the liver LDL receptor and ABCA-1 protein levels, although the SR-BI protein content was unchanged. The RCT benefit in CETP-tg mice elicited by exercise training helps to elucidate the role of exercise in the prevention of atherosclerosis in humans.     

A micro‐method for lipoprotein cholesterol profiles: Impact of CETP in KKAy mice

The aim of the present study was to assess cholesterol‐containing lipoprotein profiles in minute serum samples. The lipoprotein profiles of KKA^y and transgenic KKA^y‐CETP mice and of other species were determined. The transgenic KKA^y‐CETP mice express the simian enzyme cholesteryl ester transfer protein (CETP). The serum profile of the cholesterol‐containing high‐density (HDL), low‐density (LDL) and very‐low‐density lipoproteins (VLDL) was monitored on a Superose 6 column using fast protein liquid chromatography. Serum from several mouse and rat strains, rabbit, hamster, pig and man was included for comparative and method validation purposes. The chromatograms showed that the transgenic KKA^y‐CETP mice had significantly decreased relative levels of HDL vs. VLDL and LDL cholesterol (p <0.001). Introduction of the CETP gene shifted the serum profile of the cholesterol‐containing lipoproteins of the KKA^y‐CETP mice closer to the human profile in a dose‐dependent manner, thus making these mice an interesting model for man. The described lipoprotein separation technology offers promising and reliable opportunities for studies of blood lipoprotein profiles with minute serum samples, in both animals and man.     

Vitamin E Transfer from Lipid Emulsions to Plasma Lipoproteins: Mediation by Multiple Mechanisms

The present study determined alpha-tocopherol mass transfer from an alpha-tocopherol-rich emulsion to LDL and HDL, and assessed the potential of different mechanisms to modulate alpha-tocopherol transfers. Emulsion particles rich in alpha-tocopherol were incubated in vitro with physiological concentrations of LDL or HDL. The influence of plasma proteins was assessed by adding human lipoprotein poor plasma (LPP) fraction with intact vs heat inactivated PLTP, or with a specific cholesteryl ester transfer protein (CETP) inhibitor, or by adding purified PLTP or pig LPP which lacks CETP activity. After 4 h incubation in absence of LPP, alpha-tocopherol content was increased by ~80% in LDL and ~160% in HDL. Addition of LPP markedly enhanced alpha-tocopherol transfer leading to 350–400% enrichment in LDL or HDL at 4 h. Higher (~10 fold) enrichment was achieved after 20 h incubation with LPP. Facilitation of alpha-tocopherol transfer was (i) more than 50% higher with human vs pig LPP (despite similar PLTP phospholipid transfer activity), (ii) reduced by specific CETP activity inhibition, (iii) not fully suppressed by heat inactivation, and (iv) not restored by purified PLTP. In conclusion, alpha-tocopherol content in LDL and HDL can be markedly raised by rapid transfer from an alpha-tocopherol-rich emulsion. Our results indicate that alpha-tocopherol mass transfer between emulsion particles and lipoproteins is mediated by more than one single mechanism and that this transfer may be facilitated not only by PLTP but likely also by other plasma proteins such as CETP.     

Supplementation with a pine bark extract rich in polyphenols increases plasma antioxidant capacity and alters the plasma lipoprotein profile

Pycnogenol (PYC), an extract of French maritime pine bark (Pinus pinaster), is a potent antioxidant with potential health benefits. Its bioavailabilty has previously been shown by urinary excretion studies of constituents and metabolites of PYC. The aim of this study was to test the effect of PYC supplementation on measures of oxidative stress and the lipid profile in humans. Twenty-five healthy subjects received PYC (150 mg/d) for 6 wk. Fasting blood was collected at baseline, after 3 and 6 wk of supplementation, and again after a 4-wk washout period. After 6 wk of supplementation with PYC, a significant increase in plasma polyphenol levels was detectable, which was reversed after the 4-wk washout phase. The antioxidant effect of PYC was demonstrated by a significant increase in oxygen radical absorbance capacity (ORAC) in plasma throughout the supplementation period (P < 0.05). The ORAC value returned to baseline after the 4-wk washout period. Moreover, in addition to its antioxidant effects, PYC significantly reduced LDL-cholesterol levels and increased HDL-cholesterol levels in plasma of two-thirds of the subjects. While the LDL changes reversed during washout, the HDL increase did not. There was no significant difference in LDL oxidizability or plasma lipid peroxides following PYC supplementation. Hence, following oral supplementation in humans, PYC significantly increases antioxidant capacity of plasma, as determined by ORAC, and exerts favorable effects on the lipid profile.     

Lipoprotein Subfraction Profile and HDL-Associated Enzymes in Sickle Cell Disease Patients

Although hypocholesterolemia is a reported finding in sickle cell disease (SCD), low-density lipoprotein (LDL)/high-density lipoprotein (HDL) subfractions and HDL-associated enzymes have not been determined in SCD patients. Blood was collected from 38 hemoglobin (Hb)A volunteers and 45 homozygous HbSS patients who had not received blood transfusions in the last 3 months. Serum lipids were measured by automated analyzer while LDL and HDL subfraction analysis was done by continuous disc polyacrylamide gel electrophoresis. Serum levels of cholesteryl ester transfer protein (CETP), lecithin-cholesterol acyltransferase (LCAT), apolipoprotein B (apoB) and apolipoprotein A-1 (apoA-I) were determined by enzyme-linked immunosorbent assay (ELISA). Total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) levels were significantly decreased, while TG levels were significantly increased in SCD patients compared to controls. A significant decrease in intermediate-density lipoprotein (IDL)-C, IDL-B, IDL-A and LDL-1 fractions were seen in SCD patients, while no significant difference was observed in small dense LDL particles. A significant decrease was seen in HDL-large, HDL-intermediate and HDL-small fractions in SCD patients versus controls. Levels of LCAT and ApoA-1 protein measured in SCD patients were significantly lower while no significant difference was observed in CETP and ApoB protein levels compared to controls. The reduction observed in LDL- and HDL-C in SCD patients was reflected as significantly decreased IDL, LDL-1 and HDL-subfractions. Decreased HDL subfractions may possibly lead to the reduced ApoA-1 and LCAT protein levels observed in SCD patients.     

Peroxisome Proliferator-Activated Receptor α Agonists Regulate Cholesterol Ester Transfer Protein

Peroxisome proliferator-activated receptor alpha (PPARalpha) belongs to the nuclear receptor superfamily that regulates multiple target genes involved in lipid metabolism. Cholesterol ester transfer protein (CETP) is a secreted glycoprotein that modifies high-density lipoprotein (HDL) particles. In humans, plasma CETP activity is inversely correlated with HDL cholesterol levels. We report here that PPARalpha agonists increase CETP mRNA, protein and accordingly its activity. In a human CETP transgenic animal model harboring the natural flanking regions (Jiang et al. in J Clin Investigat 90:1290-1295, 1992), both fenofibrate and a specific synthetic PPARalpha agonist LY970 elevated human CETP mRNA in liver, serum protein and CETP activity. In hamsters, the endogenous liver CETP mRNA level and the serum CETP activity were dose-dependently upregulated by fenofibrate. In addition Wy14643, a PPARalpha agonist, also significantly elevated CETP mRNA and activity. In a carcinoma cell line of hepatic origin, HepG2 cells, overexpression of PPARalpha resulted in increased CETP mRNA and agonist treatment further elevated CETP mRNA levels. We conclude that PPARalpha agonists upregulate CETP expression and activity and may play an important role in PPARalpha (agonist mediated HDL cholesterol homeostasis in humans.     

Aerobic Training in Young Men Increases the Transfer of Cholesterol to High Density Lipoprotein In Vitro: Impact of High Density Lipoprotein Size

Exercise training not only improves the plasma lipid profile but also reduces risk of developing coronary heart disease. We investigate whether plasma lipids and high density lipoprotein (HDL) metabolism are affected by aerobic training and whether the high-density lipoprotein cholesterol (HDL-C) levels at baseline influence exercise-induced changes in HDL. Seventy-one male sedentary volunteers were evaluated and allocated in two subgroups, according to the HLD-C levels (< or >40 mg/dL). Participants underwent an 18-week aerobic training period. Blood was sampled before and after training for biochemical analysis. Plasma lipids, apolipoproteins, HDL diameter, and VO₂ peak were determined. Lipid transfers to HDL were determined in vitro by incubating plasma samples with a donor lipid artificial nanoemulsion. After the 18-week period of aerobic training, the VO₂ peak increased, while the mean body mass index (BMI) decreased. HDL-C concentration was higher after the training period, but low-density lipoprotein cholesterol (LDL-C) and non-HDL-C did not change. The transfer of esterified cholesterol and phospholipids was greater after exercise training, but the triacylglycerol and unesterified cholesterol transfers were unchanged. The HDL particle diameter increased after aerobic training in all participants. When the participants were separated in low-HDL and normal-HDL groups, the postaerobic exercise increment in HDL-C was higher in the low-HDL group, while the transfer of esterified cholesterol was lower. In conclusion, aerobic exercise training increases the lipid transfers to HDL, as measured by an in vitro method, which possibly contributes to the classical elevation of the HDL-C associated with training.     

Cholesteryl Ester Transfer Protein Impairs Triglyceride Clearance via Androgen Receptor in Male Mice

Elevated postprandial triacylglycerols (TAG) are an important risk factor for cardiovascular disease. Men have higher plasma TAG and impaired TAG clearance compared to women, which may contribute to sex differences in risk of cardiovascular disease. Understanding mechanisms of sex differences in TAG metabolism may yield novel therapeutic targets to prevent cardiovascular disease. Cholesteryl ester transfer protein (CETP) is a lipid shuttling protein known for its effects on high-density lipoprotein (HDL) cholesterol levels. Although mice lack CETP, we previously demonstrated that transgenic CETP expression in female mice alters TAG metabolism. The impact of CETP on TAG metabolism in males, however, is not well understood. Here, we demonstrate that CETP expression increases plasma TAG in males, especially in very-low density lipoprotein (VLDL), by impairing postprandial plasma TAG clearance compared to wild-type (WT) males. Gonadal hormones were required for CETP to impair TAG clearance, suggesting a role for sex hormones for this effect. Testosterone replacement in the setting of gonadectomy was sufficient to restore the effect of CETP on TAG. Lastly, liver androgen receptor (AR) was required for CETP to increase plasma TAG. Thus, expression of CETP in males raises plasma TAG by impairing TAG clearance via testosterone signaling to AR. Further understanding of how CETP and androgen signaling impair TAG clearance may lead to novel approaches to reduce TAG and mitigate risk of cardiovascular disease.     

Effect of Compounds Affecting ABCA1 Expression and CETP Activity on the HDL Pathway Involved in Intestinal Absorption of Lutein and Zeaxanthin

The antioxidant xanthophylls lutein and zeaxanthin are absorbed from the diet in a process involving lipoprotein formation. Selective mechanisms exist for their intestinal uptake and tissue‐selective distribution, but these are poorly understood. We investigated the role of high‐density lipoprotein (HDL), apolipoprotein (apo) A1 and ATP‐binding cassette transporter (ABC) A1 in intestinal uptake of lutein in a human polarized intestinal cell culture and a hamster model. Animals received dietary lutein and zeaxanthin and either a liver X receptor (LXR) agonist or statin, which up‐ or down‐regulate intestinal ABCA1 expression, respectively. The role of HDL was studied following treatment with the cholesteryl ester transfer protein (CETP) modulator dalcetrapib or the CETP inhibitor anacetrapib. In vitro, intestinal ABCA1 at the basolateral surface of enterocytes transferred lutein and zeaxanthin to apoA1, not to mature HDL. In hamsters, plasma lutein and zeaxanthin levels were markedly increased with the LXR agonist and decreased with simvastatin. Dalcetrapib, but not anacetrapib, increased plasma and liver lutein and zeaxanthin levels. ABCA1 expression and apoA1 acceptor activity are important initial steps in intestinal uptake and maintenance of lutein and zeaxanthin levels by an HDL‐dependent pathway. Their absorption may be improved by physiological and pharmacological interventions affecting HDL metabolism.     

Quantitation of baboon lipoproteins by high performance gel exclusion chromatography

High performance liquid chromatography with gel exclusion columns was used for quantitative measurement of plasma lipoproteins. A combination of columns TKS 4000 PW and 3000 PW gave good separation of very low (VLDL), low (LDL) and high (HDL) density lipoproteins. The area under each lipoprotein peak detected by absorbance at 280 nm was measured by digitizing and was expressed as cm². Purified lipoprotein standards isolated by ultracentrifugation were also chromatographed in increasing concentrations. The area under the lipoprotein standard peak was linearly related to the amount of total protein over a wide range. The areas of most of the measured plasma lipoproteins were within the linear range. The relationship between the area and the amount of protein for each standard was used to quantitate the amount of protein and was expressed as mg/dl plasma. This technique is simple and requires a small amount of plasma. The validated technique was applied to a large population of pedigreed baboons. An average plasma lipoprotein profile of feral baboons on the chow diet was characterized by a high level of HDL (90.9±30.7 mg/dl) with a lesser amount of LDL (29.1±13.2 mg/dl). VLDL was present in much lower concentration (8.6±2.6 mg/dl). Feeding a high cholesterol and high saturated fat (HCHF) diet raised both LDL (1.5-fold) and HDL levels (1.3-fold) without changing VLDL levels. Progeny of sires with low response to dietary cholesterol increased their HDL protein when challenged with HCHF diet without any change in their LDL or VLDL. Progeny of high-responding sires, however, had increases in both their HDL and LDL levels when challenged with HCHF diet. The survey of lipoprotein profiles of the pedigreed baboon colony disclosed a number of animals with interesting and unusual lipoprotein patterns.     

Regulation by long-chain fatty acids of the expression of cholesteryl ester transfer protein in HepG2 cells

Cholesteryl ester transfer protein (CETP) is an important determinant of lipoprotein function, especially high density lipoprotein (HDL) metabolism, and contributes to the regulation of plasma HDL levels. Since saturated and polyunsaturated fatty acids (FA) appear to influence the CETP activity differently, we decided to investigate the effects of FA on the expression of CETP mRNA in HepG2 cells using an RNA blot hybridization analysis. Long-chain FA (>18 carbons) at a 0.5 mM concentration were added to the medium and incubated with cells for 48 h at 37°C under 5% CO₂. After treatment with 0.5 mM arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic acid (DHA), the levels of CETP mRNA were less than 50% of the control levels (AA, P=0.0005; EPA, P<0.01; DHA, P<0.0001), with a corresponding significant decrease in the CETP mass. These results suggest that FA regulate the gene expression of CETP in HepG2 and this effect is dependent upon the degree of unsaturation of the acyl carbon chain in FA.     

Dietary sphingolipids lower plasma cholesterol and triacylglycerol and prevent liver steatosis

The prevalence of dyslipidemia and obesity resulting from excess energy intake and physical inactivity is increasing. The liver plays a pivotal role in the systemic lipid homeostasis. Effective, natural dietary interventions that lower plasma lipids and promote liver health are needed. APOE*3Leiden mice were fed a Western‐type diet, supplemented with different sphingolipids, to determine their effect on plasma lipids and liver steatosis. Hepatic lipid levels and lipid‐related gene expression were also determined. Dietary sphingolipids dose‐dependently lowered both plasma cholesterol (C) and triglycerides (TG) in APOE*3Leiden mice. 1% Phytosphingosine (PS) reduced C and TG by 57 and 58%, respectively. PS (a) decreased the absorption of dietary C and free fatty acid but did not affect the intestinal TG lipolysis, (b) increased hepatic VLDL‐TG production whereas plasma lipolysis was not affected; and (c) increased the hepatic uptake of VLDL remnants. Hepatic mRNA levels indicated enhanced hepatic lipid synthesis and VLDL and LDL uptake. Livers of PS (1%) fed mice were lighter (?22%), less pale, and contained less cholesteryl ester (?61%) and TG (?56%). Furthermore, markers for liver inflammation (SAA) and liver damage (ALAT) were decreased by 74% and 79%, respectively in PS‐fed mice. Sphingolipids lower plasma C and TG and protect the liver from fat‐ and cholesterol‐induced steatosis. In a preliminary small double‐blind cross‐over study with six middle‐aged slightly overweight male volunteers the daily supplementation of one gram of PS to the diet resulted in a ?9.8% (p = 0.0074) and – 13.2% (p = 0.0002) reduction of total C and LDL‐C, respectively. The C/HDL‐C ratio was not significantly affected (p = 0.0571). Due to the relatively low pre‐study levels of TG in the human volunteers, and the individual variability of TG levels, the TG lowering in humans was not significant in this first small study, but per individual there was a clear trend in TG lowering.     

Lipid transfers to HDL are diminished in long-term bedridden patients: association with low HDL-cholesterol and increased inflammatory markers

Plasma lipids have been extensively studied in sedentary and in subjects practicing exercise training, but not in extreme inactivity as occurs in bedridden patients. This is important for the care of bedridden patients and understanding the overall plasma lipid regulation. Here, we investigated plasma lipids, lipid transfers to HDL and inflammatory markers in bedridden patients. Fasting blood samples were collected from 23 clinically stable bedridden patients under long‐term care (>90 days) and 26 normolipidemic sedentary subjects, paired for age and gender. In vitro transfer of four lipids to HDL was performed by incubating plasma with donor nanoparticles containing radioactive lipids. Total (193 ± 36 vs 160 ± 43, p = 0.005), LDL (124 ± 3 vs 96 ± 33 p = 0.003) and HDL‐cholesterol (45 ± 10 vs 36 ± 13, p = 0.008), apolipoprotein A‐I (134 ± 20 vs 111 ± 24, p = 0.001) and oxidized LDL (53 ± 13 vs 43 ± 12, p = 0.011) were lower in bedridden patients, whereas triglycerides, apolipoprotein B, CETP and LCAT were equal in both groups. Transfers of all lipids, namely unesterified cholesterol, cholesterol esters, triglycerides and phospholipids, to HDL were lower in bedridden patients, probably due to their lower HDL‐cholesterol levels. Concentrations of IL‐1β, IL‐6, IL‐8, HGF and NGF were higher in bedridden patients compared to sedentary subjects. In conclusion, inactivity had great impact on HDL, by lowering HDL‐cholesterol, apolipoprotein A‐I and thereby cholesterol transfers to the lipoprotein, which suggests that inactivity may deteriorate HDL protection beyond the ordinary sedentary condition.     

Hypolipidemic activity of 6-alkoxycarbonyl-3-aryl-1,3,5-triazabicyclo[3.1.0]hexane-2,4-diones and 2-alkoxycarbonyl-5-aryl-1,3,5-triazine-4,6(1H,5H)-diones in rodents

Significant hypolipidemic activity was demonstrated by 6-ethoxycarbonyl-3-phenyl-1,3,5-triazabicyclo[3.1.0]hexane-2,4-dione, 2-ethoxycarbonyl-5-phenyl-1,3,5-triazine-4,6(1H,5H)-dione and 2-ethoxycarbonyl-5-(4-chlorophenyl)-1,3,5-trizine-4,6(1H,5H)-dione in rodents at 20 mg/kg/day. These agents lowered serum cholesterol and triglyceride levels by approximately 40% in mice after 16 d. Tissue lipids in rat liver, small intestinal mucosa, aortic wall and feces were reduced by treatment with the agents. Very low density lipoprotein (VLDL) and low density lipoprotein (LDL) cholesterol levels were reduced in the rat; high density lipoprotein (HDL) cholesterol levels were elevated after 14 d of treatment. The activities of regulatory enzymes,e.g., acetyl-CoA synthetase, acyl-CoA:cholesterol acyltransferase, cholesterol 7α-hydroxylase,sn-glycerol-3-phosphate acyltransferase, phosphatidylate phosphohydrolase and heparin-induced lipoprotein lipase, involved inde novo synthesis of hepatic lipids were affected by the agents. The new compounds may represent another class of potentially useful hypolipidemic agents for the treatment of atherosclerosis since HDL cholesterol levels were increased and VLDL and LDL cholesterol levels were lowered by some of the agents.     

Treatment of Low HDL‐C Subjects with the CETP Modulator Dalcetrapib Increases Plasma Campesterol Only in Those Without ABCA1 and/or ApoA1 Mutations

We investigated the effect of dalcetrapib treatment on phytosterol levels in patients with familial combined hyperlipidemia (FCH) or familial hypoalphalipoproteinemia (FHA) due to mutations in apolipoprotein A1 (ApoA1) or ATP‐binding cassette transporter A1 (ABCA1). Patients (n = 40) with FCH or FHA received dalcetrapib 600 mg or placebo in this 4‐week, double‐blind, crossover study. Lipids, apolipoproteins, cholesteryl ester transfer protein (CETP) activity and mass, and phytosterols were assessed. Dalcetrapib increased high‐density lipoprotein cholesterol (HDL‐C) and ApoA1 levels to a similar extent in FHA (+22.8, +13.9 %) and FCH (+18.4, +12.1 %), both p < 0.001 vs. placebo. Changes in CETP activity and mass were comparable for FHA (?31.5, +120.9 %) and FCH (?26.6, +111.9 %), both p < 0.0001 vs. placebo. Campesterol and lathosterol were unchanged in FHA (+3.8, +3.0 %), but only campesterol was markedly increased in FCH (+25.0 %, p < 0.0001 vs. placebo). Campesterol increased with dalcetrapib treatment in FCH but not in FHA, despite comparable HDL‐C and ApoA1 increases, suggesting that ApoA1 and/or ABCA1 is essential for HDL lipidation by enterocytes in humans.     

Sage Tea Drinking Improves Lipid Profile and Antioxidant Defences in Humans

Salvia officinalis (common sage) is a plant with antidiabetic properties. A pilot trial (non-randomized crossover trial) with six healthy female volunteers (aged 40–50) was designed to evaluate the beneficial properties of sage tea consumption on blood glucose regulation, lipid profile and transaminase activity in humans. Effects of sage consumption on erythrocytes’ SOD and CAT activities and on Hsp70 expression in lymphocytes were also evaluated. Four weeks sage tea treatment had no effects on plasma glucose. An improvement in lipid profile was observed with lower plasma LDL cholesterol and total cholesterol levels as well as higher plasma HDL cholesterol levels during and two weeks after treatment. Sage tea also increased lymphocyte Hsp70 expression and erythrocyte SOD and CAT activities. No hepatotoxic effects or other adverse effects were observed.     

Plasma HDL Reduces Nonesterified Fatty Acid Hydroperoxides Originating from Oxidized LDL: a Mechanism for Its Antioxidant Ability

The antioxidant property of plasma high-density lipoprotein (HDL) is thought to be involved in potential anti-atherogenic effects but the exact mechanism is not known. We aimed to reveal the contribution of HDL on the elimination of lipid hydroperoxides (LOOH) derived from oxidized low-density lipoprotein (LDL). Oxidized LDL prepared by copper ion-induced oxidation contained nonesterified fatty acid hydroperoxides (FFA-OOH) and lysophosphatidylcholine (lysoPtdCho), in addition to cholesteryl ester hydroperoxides (CE-OOH) and phosphatidylcholine hydroperoxides (PtdCho-OOH). A platelet-activating factor-acetylhydrolase (PAF-AH) inhibitor suppressed formation of FFA-OOH and lysoPtdCho in oxidized LDL. Among LOOH species, FFA-OOH was preferentially reduced by incubating oxidized LDL with HDL. HDL exhibited selective FFA-OOH reducing ability if it was mixed with a liposomal solution containing FFA-OOH, CE-OOH and PtdCho-OOH. Two-electron reduction of the hydroperoxy group to the hydroxy group was confirmed by the formation of 13-hydroxyoctadecadienoic acid from 13-hydroperoxyoctadecadienoic acid in HPLC analyses. This reducing effect was also found in apolipoprotein A-1 (apoA-1). FFA-OOH released from PtdCho-OOH due to PAF-AH activity in oxidized LDL undergo two-electron reduction by the reducing ability of apoA1 in HDL. This preferential reduction of FFA-OOH may participate in the mechanism of the antioxidant property of HDL.     

Interaction of CETP inhibitory peptide and lipoprotein substrates in cholesteryl ester transfer assay: relationship between association properties and inhibitory activities

In a previous study, CETP inhibitory peptide (3 kDa) was isolated from hog plasma. The peptide, synthesized chemically according to the amino acid sequence of the 3-kDa peptide (designated P₂₈), showed CETP inhibitory activity both in vitro and in vivo [Cho et al. (1998) Biochim. Biophys. Acta 1391, 133–144]. We report herein further unique features of P₂₈ when it was associated with the cholesteryl ester (CE)-donor and-acceptor lipoproteins. Lipoprotein substrates with P₂₈ present in both HDL (as a CE-donor) and LDL (as a CE-acceptor) served as poor substrates, with CE-transfer activity decreased up to 60% compared to normal substrates without P₂₈. P₂₈ was found to be located in HDL fractions of hog plasma and showed the same electromobility as that visualized by PAGE on 7% polyacrylamide gel under nondenaturing conditions. Addition of apolipoprotein A-1 (apoA-1) or apoB antibody to a normal CE-transfer mixture did not alter CE-transfer activity. However, addition of apoA-1 or −B antibody to a CETP-inhibition mixture decreased the inhibitory activity of P₂₈ by ca. 20%. Western blot analysis revealed that P₂₈ was associated only with human and hog HDL among several lipoproteins purified from human, hog, and rabbit. CFTP-inhibition assays with various lipoprotein substrates revealed that P₂₈ exhibited substrate-specific inhibitory activity. The inhibitory activity of P₂₈ was highly dependent on the type of lipoprotein substrate (whether CE-donor or-acceptor); P₂₈ inhibited CE transfer from HDL to LDL, but it did not inhibit CE transfer from HDL to HDL.     

Exercise and postprandial lipid metabolism – an analysis of the current evidence

Exaggerated levels of postprandial lipaemia are implicated in the atherosclerotic disease process and are a risk marker for cardiovascular disease. Postprandial lipaemia is reduced following an exercise session and the energy expended during exercise is an important determinant of the extent of triglyceride (TG) lowering. Interestingly, the TG‐lowering effect of an exercise session cannot be replicated by restricting energy intake to elicit a similar level of energy deficit. It seems likely that the low levels of postprandial lipaemia experienced by endurance‐trained individuals are largely due to the TG‐lowering effects of individual exercise sessions, rather than long‐term training adaptations, although trained individuals may also benefit from the hypotriglyceridaemic effects of having low levels of body fat. Increased lipoprotein lipase‐mediated TG clearance and reduced hepatic TG secretion are both likely to contribute to the TG reductions seen following an exercise session, but the relative importance of these two mechanisms is likely to depend on a number of factors including the energy expended during exercise and the training status of the exercising subject. Further study is needed to determine the effectiveness of exercise in reducing postprandial lipaemia in groups at increased risk for cardiovascular disease and to assess the impact of these lipoprotein changes on other aspects of cardiovascular risk.     

Response of plasma lipids to dietary cholesterol and wine polyphenols in rats fed polyunsaturated fat diets

This experiment was designed to evaluate the effects of dietary red wine phenolic compounds (WP) and cholesterol on lipid oxidation and transport in rats. For 5 wk, weanling rats were fed polyunsaturated fat diets (n−6/n−3=6.4) supplemented or not supplemented with either 3 g/kg diet of cholesterol, 5 g/kg diet of WP, or both. The concentrations of triacylglycerols (TAG, P<0.01) and cholesterol (P<0.0002) were reduced in fasting plasma of rats fed cholesterol despite the cholesterol enrichment of very low density lipoprotein + low density lipoprotein (VLDL+LDL). The response was due to the much lower plasma concentration of high density lipoprotein (HDL) (−35%, P<0.0001). In contrast, TAG and cholesteryl ester (CE) accumulated in liver (+120 and +450%, respectively, P<0.0001). However, the cholesterol content of liver microsomes was not affected. Dietary cholesterol altered the distribution of fatty acids mainly by reducing the ratio of arachidonic acid to linoleic acid (P<0.0001) in plasma VLDL+LDL (−35%) and HDL (−42%) and in liver TAG (−42%), CE (−78%), and phospholipids (−28%). Dietary WP had little or no effect on these variables. On the other hand, dietary cholesterol lowered the α-tocopherol concentration in VLDL+LDL (−40%, P<0.003) and in microsomes (−60%, P<0.0001). In contrast, dietary WP increased the concentration in microsomes (+21%, P<0.0001), but had no effect on the concentration in VLDL+LDL. Cholesterol feeding decreased (P<0.006) whereas WP feeding increased (P<0.0001) the resistance of VLDL+LDL to copper-induced oxidation. The production of conjugated dienes after 25 h of oxidation ranged between 650 (WP without cholesterol) and 2,560 (cholesterol without WP) μmol/g VLDL+LDL protein. These findings show that dietary WP were absorbed at sufficient levels to contribute to the protection of polyunsaturated fatty acids in plasma and membranes. They could also reduce the consumption of α-tocopherol and endogenous antioxidants. The responses suggest that, in humans, these substances may be beneficial by reducing the deleterious effects of a dietary overload of cholesterol.