Dietary modification of high density lipoprotein phospholipid and influence on cellular cholesterol efflux

Effects of a dietary intervention with Mediterranean vs lacto-ovo vegetarian diets on HDL function: Results from the CARDIVEG study

BACKGROUND AND AIM

HDL-cholesterol efflux capacity (CEC) has been shown to be a better cardiovascular (CVD) risk marker than serum HDL concentration. Several foods and nutrients have been shown to improve HDL functions, however no effective dietetic nor pharmacological strategy is available to increase CEC. This study aims to evaluate the possible effect of Mediterranean diet (MD) and lacto-ovo-vegetarian diet (VD) on HDL function in a group of clinically healthy subjects at low-to-moderate CVD risk.

METHODS AND RESULTS

Thirty apparently healthy subjects with a low-to-moderate cardiovascular risk profile (21 F; mean age: 51.3 ± 9.7 years) were randomly assigned to a 3-month MD or VD diet and then crossed. Participants on VD showed a reduction in total HDL CEC by 8.99% (p < 0.001) as well as a reduction in ABCA1 mediated-CEC by 18.62% (p < 0.001) compared to participants on MD. Regarding CEC mediated by aqueous diffusion, no significant changes were observed after treatment with either diet. Finally, a significant positive association between CEC mediated by the ABCA1 transporter and adiponectin was found (r = 0.462; p = 0.010).

CONCLUSION

The results of this study suggest that HDL activity in promoting cholesterol efflux and thereby reducing the concentration of pro-atherogenic lipoproteins was more effective in participants undergoing MD than VD. Based on these findings, the MD could be considered a better therapeutic strategy for cardiovascular prevention than VD.

CLINICAL TRIAL REGISTRATION URL

http://www.

CLINICALTRIALS

gov. Unique identifier: NCT02641834.

Modification of High-Density Lipoprotein Functions by Diet and Other Lifestyle Changes: A Systematic Review of Randomized Controlled Trials

High-density lipoprotein (HDL) functional traits have emerged as relevant elements that may explain HDL antiatherogenic capacity better than HDL cholesterol levels. These properties have been improved in several lifestyle intervention trials. The aim of this systematic review is to summarize the results of such trials of the most commonly used dietary modifications (fatty acids, cholesterol, antioxidants, alcohol, and calorie restriction) and physical activity. Articles were screened from the Medline database until March 2021, and 118 randomized controlled trials were selected. Results from HDL functions and associated functional components were extracted, including cholesterol efflux capacity, cholesteryl ester transfer protein, lecithin-cholesterol acyltransferase, HDL antioxidant capacity, HDL oxidation status, paraoxonase-1 activity, HDL anti-inflammatory and endothelial protection capacity, HDL-associated phospholipase A2, HDL-associated serum amyloid A, and HDL-alpha-1-antitrypsin. In mainly short-term clinical trials, the consumption of monounsaturated and polyunsaturated fatty acids (particularly omega-3 in fish), and dietary antioxidants showed benefits to HDL functionality, especially in subjects with cardiovascular risk factors. In this regard, antioxidant-rich dietary patterns were able to improve HDL function in both healthy individuals and subjects at high cardiovascular risk. In addition, in randomized trial assays performed mainly in healthy individuals, reverse cholesterol transport with ethanol in moderate quantities enhanced HDL function. Nevertheless, the evidence summarized was of unclear quality and short-term nature and presented heterogeneity in lifestyle modifications, trial designs, and biochemical techniques for the assessment of HDL functions. Such findings should therefore be interpreted with caution. Large-scale, long-term, randomized, controlled trials in different populations and individuals with diverse pathologies are warranted.

Impact of Dietary Lipids on the Reverse Cholesterol Transport: What We Learned from Animal Studies

Reverse cholesterol transport (RCT) is a physiological mechanism protecting cells from an excessive accumulation of cholesterol. When this process begins in vascular macrophages, it acquires antiatherogenic properties, as has been widely demonstrated in animal models. Dietary lipids, despite representing a fundamental source of energy and exerting multiple biological functions, may induce detrimental effects on cardiovascular health. In the present review we summarize the current knowledge on the mechanisms of action of the most relevant classes of dietary lipids, such as fatty acids, sterols and liposoluble vitamins, with effects on different steps of RCT. We also provide a critical analysis of data obtained from experimental models which can serve as a valuable tool to clarify the effects of dietary lipids on cardiovascular disease.

High-Density Lipoprotein Proteomic Composition, and not Efflux Capacity, Reflects Differential Modulation of Reverse Cholesterol Transport by Saturated and Monounsaturated Fat Diets

BACKGROUND

Acute inflammation impairs reverse cholesterol transport (RCT) and reduces high-density lipoprotein (HDL) function in vivo. This study hypothesized that obesity-induced inflammation impedes RCT and alters HDL composition, and investigated if dietary replacement of saturated (SFA) for monounsaturated (MUFA) fatty acids modulates RCT.

METHODS AND RESULTS

Macrophage-to-feces RCT, HDL efflux capacity, and HDL proteomic profiling was determined in C57BL/6j mice following 24 weeks on SFA- or MUFA-enriched high-fat diets (HFDs) or low-fat diet. The impact of dietary SFA consumption and insulin resistance on HDL efflux function was also assessed in humans. Both HFDs increased plasma (3)H-cholesterol counts during RCT in vivo and ATP-binding cassette, subfamily A, member 1-independent efflux to plasma ex vivo, effects that were attributable to elevated HDL cholesterol. By contrast, ATP-binding cassette, subfamily A, member 1-dependent efflux was reduced after both HFDs, an effect that was also observed with insulin resistance and high SFA consumption in humans. SFA-HFD impaired liver-to-feces RCT, increased hepatic inflammation, and reduced ABC subfamily G member 5/8 and ABC subfamily B member 11 transporter expression in comparison with low-fat diet, whereas liver-to-feces RCT was preserved after MUFA-HFD. HDL particles were enriched with acute-phase proteins (serum amyloid A, haptoglobin, and hemopexin) and depleted of paraoxonase-1 after SFA-HFD in comparison with MUFA-HFD.

CONCLUSIONS

Ex vivo efflux assays validated increased macrophage-to-plasma RCT in vivo after both HFDs but failed to capture differential modulation of hepatic cholesterol trafficking. By contrast, proteomics revealed the association of hepatic-derived inflammatory proteins on HDL after SFA-HFD in comparison with MUFA-HFD, which reflected differential hepatic cholesterol trafficking between groups. Acute-phase protein levels on HDL may serve as novel biomarkers of impaired liver-to-feces RCT in vivo.

Dietary approaches to improving atheroprotective HDL functions

High-density lipoproteins (HDL) are known to protect against cardiovascular disease (CVD). In addition to facilitating reverse cholesterol transport to remove excess lipids from the body - including atherosclerotic plaques - HDL exhibits antioxidant, anti-inflammatory, vasodilatory, and antithrombotic activities. Together, these properties contribute to the overall atheroprotective nature of HDL. However, similar to many other physiological pathways, these HDL parameters are known to become dysregulated in conditions of metabolic disease. Further, research suggests these alternative HDL properties may be regulated independently of blood HDL-cholesterol (HDL-C) levels, and must therefore be considered when designing HDL-targeted therapies. To date, a number of dietary strategies have been investigated to assess the effect of dietary components on functional properties of HDL beyond HDL-C. This review will highlight the bioactive nutrients, functional foods, and dietary programs known to modulate HDL function as a means of reducing CVD.

The Cholesterol Content of Western Diets Plays a Major Role in the Paradoxical Increase in High-Density Lipoprotein Cholesterol and Upregulates the Macrophage Reverse Cholesterol Transport Pathway

Objective—

A high–saturated fatty acid– and cholesterol-containing (HFHC) diet is considered to be a major risk factor for cardiovascular disease. The present study aimed to determine the effects of this Western-type diet on high-density lipoprotein (HDL) metabolism and reverse cholesterol transport (RCT) from macrophages to feces.

Methods and Results—

Experiments were carried out in mice fed a low-fat, low-cholesterol diet, an HFHC diet, or an HFHC diet without added cholesterol (high–saturated fatty acid and low-cholesterol [HFLC]). The HFHC diet caused a significant increase in plasma cholesterol, HDL cholesterol, and liver cholesterol and enhanced macrophage-derived [ 3 H]cholesterol flux to feces by 3- to 4-fold. These effects were greatly reduced in mice fed the HFLC diet. This HFHC diet–mediated induction of RCT was sex independent and was not associated with obesity or insulin resistance. The HFHC diet caused 1.4- and 3-fold increases in [ 3 H]cholesterol efflux to plasma and HDL-derived [ 3 H]tracer fecal excretion, respectively. Unlike a low-fat, low-cholesterol and HFLC diets, the HFHC diet increased liver ABCG5/G8 expression. The effect of the HFHC diet on fecal macrophage-derived [ 3 H]cholesterol excretion was totally blunted in ABCG5/G8-deficient mice.

Conclusion—

Despite its deleterious effects on atherosclerosis, the HFHC diet promoted a sustained compensatory macrophage-to-feces RCT. Our data provide direct evidence of the crucial role of dietary cholesterol signaling through liver ABCG5/G8 upregulation in the HFHC diet–mediated induction of macrophage-specific RCT.

A low‐saturated‐fat, low‐cholesterol diet decreases plasma CETP activity and pre β‐HDL formation but does not affect cellular cholesterol efflux to plasma from type 1 diabetic patients

The aim of this study was to evaluate the effect of a low-saturated-fat, low-cholesterol diet on plasma lipopoproteins, pre beta-high density lipoprotein (HDL) formation, lecithin:cholesterol acyltransferase (LCAT), cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) activities, as well as on the ability of plasma to stimulate cellular cholesterol efflux. Twelve male type 1 diabetic patients with plasma cholesterol >5.0 mmol/L were studied while consuming their usual diet and after 6 weeks of a low-fat, low-cholesterol diet. Pre beta-HDL formation was measured using crossed immuno-electrophoresis. Plasma LCAT, CETP and PLTP activities were assayed by exogenous substrate methods. The ability of plasma to promote cellular cholesterol efflux out of Fu5AH rat hepatoma cells and out of human skin fibroblasts was also determined. Saturated fat intake was lowered (p = 0.001) due to replacement with carbohydrates, while mono- and polyunsaturated fat intake remained unchanged. Cholesterol intake decreased as well (p = 0.003). The changes in plasma total cholesterol, very low and low-density lipoprotein (VLDL+LDL) cholesterol, HDL cholesterol, HDL phospholipids, apolipoprotein (apo) A-I, plasma LCAT activity and PLTP activity were not significant. Plasma CETP activity (p = 0.008) and pre beta-HDL formation (p = 0.008) decreased. The ability of plasma to promote cholesterol efflux out of fibroblasts and Fu5AH cells remained unchanged. Reduction in dietary saturated fat and cholesterol intake does not adversely affect cellular cholesterol efflux to plasma from type 1 diabetic patients, despite a drop in pre beta-HDL formation.

Macrophage cholesterol efflux elicited by human total plasma and by HDL subfractions is not affected by different types of dietary fatty acids

BACKGROUND

Plasma HDL concentrations and composition, important predictors of coronary heart disease, are modified by fatty acids (FAs) in high-fat diets.

OBJECTIVE

Following the National Cholesterol Education Program Adult Treatment Panel III recommendation that 25%-30% of total calorie intake be in the form of fat, we compared the results of the intake of 30% of energy as fat in diets enriched with trans, polyunsaturated, or saturated FAs. These dietary effects on the composition and ability of HDL(2), HDL(3), and total plasma to efflux cholesterol from mouse peritoneal macrophages that previously were loaded with LDL-acetylated 14C-cholesteryl ester were evaluated by using ultracentrifugally isolated lipoproteins.

DESIGN

After a 2-wk run-in period, 30 healthy persons (9 M, 21 F), were randomly distributed among 3 groups (n = 10/group) and fed for 4 wk with either an 8.3% trans FA, a 14.6% polyunsaturated FA, or a 13.2% saturated FA diet. The 3 diets had similar proportions of monounsaturated FAs.

RESULTS

The percentage of radioactive cell cholesterol removal did not vary among these diets, possibly because of the small difference in the composition of the HDL fraction elicited by the different diets. However, the percentage was consistently higher for HDL(3) than for HDL(2).

CONCLUSION

Differences in the cell cholesterol efflux with these diets were not observed, probably because the changes in the HDL composition were quite modest as a result of the limitation of the fat intake to 30% of total calories and because of the rigorous control of the proportions of FAs in the experimental diets used in this investigation.

Effects of dietary maritime pine (Pinus pinaster)-seed oil on high-density lipoprotein levels and in vitro cholesterol efflux in mice expressing human apolipoprotein A-I

Maritime pine (Pinus pinaster)-seed oil contains two Δ5 unsaturated polymethylene interrupted fatty acids (all cis-5,9,12–18:3 and all cis-5,11,14–20:3 acids) one of which resembles eicosapentaenoic acid. The goal of the present study was to test whether maritime pine-seed oil consumption affects HDL and apolipoprotein (Apo) A-I levels as well as the ability of serum to promote efflux of cholesterol from cultured cells. To this end, wild type (WT) non-transgenic mice and transgenic mice expressing human ApoA-I (HuA-ITg) were fed on isoenergetic diet containing either 200 g maritime pine-seed oil/kg or 200 g lard/kg for 2 weeks. WT and HuA-ITg mice fed maritime pine-seed oil had lower cholesterol, HDL-cholesterol, LDL-cholesterol and HuA-ITg mice had lower human ApoA-I than those fed lard. The differences in cholesterol (P < 0·0001) and HDL-cholesterol (P < 0·003) levels between mice fed on the two diets were more pronounced in the HuA-ITg than in the WT mice. The ability of HuA-ITg serum to promote cholesterol efflux in cultured cells was greater (P < 0·008) than that of WT animals. However, the maritime pine-seed oil diet was associated with lower (P < 0·005) in vitro cholesterol efflux ability than the lard diet in both mice genotypes. This suggests a negative effect of the maritime pine-seed oil on reverse cholesterol transport. Cholesterol efflux was correlated with serum free or esterified cholesterol and phospholipid levels. The slope of the regression line was smaller in the HuA-ITg than in the WT mice indicating that overexpression of human ApoA-I reduces the negative impact of maritime pine-seed oil on cholesterol efflux. In conclusion, maritime pine-seed oil diet lowers HDL-cholesterol and diminishes in vitro cholesterol efflux. This potentially detrimental effect is attenuated by overexpression of human ApoA-I in mice.

Reverse cholesterol transport is regulated by varying fatty acyl chain saturation and sphingomyelin content in reconstituted high-density lipoproteins

Because phospholipid composition of high-density lipoprotein (HDL) plays a vital role in its reverse cholesterol transport (RCT) function, we studied RCT in vitro (uptake and efflux) with reconstituted HDLs (rHDLs) containing phosphatidylcholine (PC) with fatty acids of increasing saturation levels (stearic, oleic, linoleic, linolenic) and without or with sphingomyelin (SM). Uptake significantly increased from basal value when the PC component included up to 50 mol % of oleic or linolenic acid, but did not change with linoleic acid. Increasing oleic and linoleic acids to 100 mol % significantly decreased uptake, but increasing linolenic acid to the same value did not affect it. Sphingomyelin in rHDL significantly decreased uptake, but only with PC-containing unsaturated fatty acids, and not with saturated fatty acid. Efflux was not affected in a dose-dependent manner when oleic or linoleic acid content was increased, but was significantly increased with levels of linolenic acid up to 25 mol % in PC, and was dramatically lowered with higher levels. Sphingomyelin in rHDL (PC/SM, 20:80, mol/mol) significantly increased efflux only with oleic or linoleic acid-containing rHDLs, compared with efflux without SM. In conclusion, enrichment of PC component up to 25 mol % as linolenic acid has a beneficial effect on RCT, whereas a higher percentage of it or other unsaturated fatty acids seems to be detrimental. In addition, high SM content decreases uptake with rHDL-containing unsaturated fatty acids, whereas it increases efflux for rHDL-containing oleic or linoleic acid. These results show for the first time the importance of SM in RCT in a well-defined in vitro system.

Sunflower oil does not protect against LDL oxidation as virgin olive oil does in patients with peripheral vascular disease

BACKGROUND & AIMS

The aim of this study was to compare the in vivo effects of a diet rich in virgin olive oil or sunflower oil on the lipid profile and on LDL susceptibility to oxidative modification in free-living Spanish male patients with peripheral vascular disease.

METHODS

A total of 20 Spanish male subjects diagnosed with peripheral vascular disease were randomly divided into two groups (n = 10) receiving different supplements, virgin olive oil and sunflower oil for 4 months.

RESULTS

The adaptation of patients to the experimental supplements was demonstrated since plasma and LDL fatty acids composition reflected dietary fatty acids. No differences in triglycerides, total cholesterol, LDL-cholesterol or HDL-cholesterol concentrations were found between the groups of patients. A significantly higher LDL susceptibility to oxidation was observed after sunflower oil intake in comparison with virgin olive oil, in spite of an increase in LDL alpha-tocopherol concentration in sunflower oil group.

CONCLUSIONS

The results of the present study provide further evidence that sunflower-oil-enriched diets does not protect LDL against oxidation as virgin olive oil does in patients with peripheral vascular disease.

Dietary Hydrogenated Fat Increases High-Density Lipoprotein apoA-I Catabolism and Decreases Low-Density Lipoprotein apoB-100 Catabolism in Hypercholesterolemic Women

OBJECTIVE

To determine mechanisms contributing to decreased high-density lipoprotein cholesterol (HDL-C) and increased low-density lipoprotein cholesterol (LDL-C) concentrations associated with hydrogenated fat intake, kinetic studies of apoA-I, apoB-100, and apoB-48 were conducted using stable isotopes.

METHODS AND RESULTS

Eight postmenopausal hypercholesterolemic women were provided in random order with 3 diets for 5-week periods. Two-thirds of the fat was soybean oil (unsaturated fat), stick margarine (hydrogenated fat), or butter (saturated fat). Total and LDL-C levels were highest after the saturated diet (P<0.05; saturated versus unsaturated) whereas HDL-C levels were lowest after the hydrogenated diet (P<0.05; hydrogenated versus saturated). Plasma apoA-I levels and pool size (PS) were lower, whereas apoA-I fractional catabolic rate (FCR) was higher after the hydrogenated relative to the saturated diet (P<0.05). LDL apoB-100 levels and PS were significantly higher, whereas LDL apoB-100 FCR was lower with the saturated and hydrogenated relative to the unsaturated diet. There was no significant difference among diets in apoA-I or B-100 production rates or apoB-48 kinetic parameters. HDL-C concentrations were negatively associated with apoA-I FCR (r=-0.56, P=0.03) and LDL-C concentrations were negatively correlated with LDL apoB-100 FCR (r=-0.48, P=0.05).

CONCLUSIONS

The mechanism for the adverse lipoprotein profile observed with hydrogenated fat intake is determined in part by increased apoA-I and decreased LDL apoB-100 catabolism.

Reduction of dietary saturated fatty acids correlates with increased plasma lecithin cholesterol acyltransferase activity in humans

OBJECTIVE

Increased HDL-cholesterol (HDL-C) concentrations have been associated with lower coronary heart disease risk. On the other hand, dietary fats are known to influence the fatty acid profile of plasma lipids, including phospholipids that are substrates of lecithin cholesterol acyltransferase (LCAT), an important enzyme in HDL metabolism. The purpose of this study was to examine the association between the saturated fatty acid (SFA) intake and LCAT activity.

DESIGN

An interventional study was performed in a monk community of 25 men.

SETTING

A French monk community, South West of France.

SUBJECTS AND INTERVENTIONS

The basal diet of the study cohort contained SFA in a proportion of 13.5% of their total energy intake (TEI). They were submitted to two experimental isocaloric diets containing either 8.4% of the TEI in SFA (diet A) or 11% (diet B), each lasting 5 weeks.

RESULTS

The elevation of SFA in diet B was mainly obtained by decreasing carbohydrates. The only significant difference among total fats between diets A and B was the myristic acid content (0.6 and 1.2% of TEI, respectively). The elevation in SFA in diet B resulted in a significant increase of HDL-C (P<0.04), while plasma apo A-I concentration and LCAT activity both decreased (P<0.02).

CONCLUSION

Altogether, these results are consistent with a negative effect of SFA on reverse cholesterol transport.

Targeted deletion of the ileal bile acid transporter eliminates enterohepatic cycling of bile acids in mice

The ileal apical sodium bile acid cotransporter participates in the enterohepatic circulation of bile acids. In patients with primary bile acid malabsorption, mutations in the ileal bile acid transporter gene (Slc10a2) lead to congenital diarrhea, steatorrhea, and reduced plasma cholesterol levels. To elucidate the quantitative role of Slc10a2 in intestinal bile acid absorption, the Slc10a2 gene was disrupted by homologous recombination in mice. Animals heterozygous (Slc10a2+/-) and homozygous (Slc10a2-/-) for this mutation were physically indistinguishable from wild type mice. In the Slc10a2-/- mice, fecal bile acid excretion was elevated 10- to 20-fold and was not further increased by feeding a bile acid binding resin. Despite increased bile acid synthesis, the bile acid pool size was decreased by 80% and selectively enriched in cholic acid in the Slc10a2-/- mice. On a low fat diet, the Slc10a2-/- mice did not have steatorrhea. Fecal neutral sterol excretion was increased only 3-fold, and intestinal cholesterol absorption was reduced only 20%, indicating that the smaller cholic acid-enriched bile acid pool was sufficient to facilitate intestinal lipid absorption. Liver cholesteryl ester content was reduced by 50% in Slc10a2-/- mice, and unexpectedly plasma high density lipoprotein cholesterol levels were slightly elevated. These data indicate that Slc10a2 is essential for efficient intestinal absorption of bile acids and that alternative absorptive mechanisms are unable to compensate for loss of Slc10a2 function.

Effects of LDL enriched with different dietary fatty acids on cholesteryl ester accumulation and turnover in THP-1 macrophages

LDL enriched with either saturated, monounsaturated, n-6 polyunsaturated, or n-3 polyunsaturated fatty acids were used to study the effects of dietary fatty acids on macrophage cholesteryl ester (CE) accumulation, physical state, hydrolysis, and cholesterol efflux. Incubation of THP-1 macrophages with acetylated LDL (AcLDL) from each of the four diet groups resulted in both CE and triglyceride (TG) accumulation, in addition to alterations of cellular CE, TG, and phospholipid fatty acyl compositions reflective of the individual LDLs. Incubation with monounsaturated LDL resulted in significantly higher total and CE accumulation when compared with the other groups. After TG depletion, intracellular anisotropic lipid droplets were visible in all four groups, with 71% of the cells incubated with monounsaturated AcLDL containing anisotropic lipid droplets, compared with 30% of cells incubated with n-3 AcLDL. These physical state differences translated into higher rates of both CE hydrolysis and cholesterol efflux in the n-3 group. These data suggest that monounsaturated fatty acids may enhance atherosclerosis by increasing both cholesterol delivery to macrophage foam cells and the percentage of anisotropic lipid droplets, while n-3 PUFAs decrease atherosclerosis by creating more fluid cellular CE droplets that accelerate the rate of CE hydrolysis and the efflux of cholesterol from the cell.

Transgenic overexpression of human lecithin: cholesterol acyltransferase (LCAT) in mice does not increase aortic cholesterol deposition

Results from several atherosclerosis studies using morphometric procedures have proven controversial with regard to whether over-expression of human LCAT in transgenic (Tg) mice is atherogenic. The purpose of the present study was to determine the effect of 10-fold over-expression of human LCAT on aortic free and esterified cholesterol (EC) deposition as well as plasma lipoprotein cholesteryl ester (CE) fatty acid composition in mice fed an atherogenic diet containing cholic acid. C57Bl/6 (control) and human LCAT-Tg mice were fed chow or an atherogenic diet (15% of calories from palm oil, 1.0% cholesterol and 0.5% cholic acid) for 24 weeks before measurement of aortic cholesterol content. Compared with the chow diet, control and LCAT-Tg mice fed the atherogenic diet had a 2-fold increase in plasma total, free and EC, a 7-fold increase in plasma apoB lipoprotein cholesterol, and a 40-50-fold increase in hepatic cholesterol content. The aortic EC content was increased in control (0.7 vs. 1.2 mg/g protein) and LCAT-Tg (0.3 vs. 1.5 mg/g protein) mice fed the atherogenic diet compared with those consuming the chow diet; however, there was no difference in aortic free (14.4+/-6.8 vs. 18.5+/-7.7 mg/g protein) or esterified (1.2+/-1.0 vs. 1.5+/-1.2 mg/g protein) cholesterol content between atherogenic diet-fed control and LCAT-Tg mice, respectively. LCAT-Tg mice fed the atherogenic diet had a 2-fold increase in the ratio of saturated+monounsaturated to polyunsaturated CE species in plasma apoB lipoproteins compared with control mice (9.4+/-2.4 vs. 4.9+/-0.7). We conclude that over-expression of human LCAT in Tg mice fed an atherogenic diet containing cholic acid does not result in increased aortic cholesterol deposition compared with control mice, even though the CE fatty acid saturation index of plasma apoB lipoproteins was doubled.

n-3 FA increase liver uptake of HDL-cholesterol in mice

In humans, diets rich in fish oil (containing n-3 FA) decrease the incidence of coronary artery diseases. This is thought to be caused by the induction in liver and skeletal muscle of genes involved in lipid oxidation, and to the repression in liver and adipose tissue of genes responsible for lipogenesis. n-3 FA are known to reduce the synthesis of FA and TG in the liver, resulting in a decrease of plasma concentrations of TG-rich lipoproteins. On the other hand, little is known of a possible effect of n-3 FA on HDL metabolism. To investigate this question, female C57Bl/6J mice were fed an n-3 FA-enriched diet for 16 wk. As expected from previous studies, we found that total cholesterol, TG, and phospholipids were reduced in the plasma of treated mice. We also found that HDL-cholesterol decreased after this treatment and that the in vivo fractional catabolic rate of HDL-cholesteryl ester was significantly higher in treated mice than in control mice fed a standard diet. Consistent with these results, treated mice exhibited increased uptake of HDL-cholesteryl ester in the liver. Moreover, quantitative reverse transcriptase-PCR analysis showed a two- to threefold increase in scavenger receptor B-1 gene expression. Taken together, these results suggest that an n-3 FA-enriched diet stimulates one step in the reverse cholesterol transport in mice, probably by increasing the amount of the scavenger receptor class B-1. These effects of n-3 FA on HDL metabolism may contribute to their beneficial effects on the vasculature.

Trans fatty acids affect lipoprotein metabolism in rats

This study was designed to investigate the effects of oleic (CIS), palmitic (SAT) and trans fatty acids (TRANS) on cholesterol metabolism. Rats fed the TRANS diet had lower plasma total cholesterol (P < 0.005) and non-HDL-cholesterol (non HDL-C) concentrations (P < 0.005) compared with their CIS-fed counterparts. Plasma HDL-C was highest in rats fed the SAT diet (P = 0.01). An in vivo assay of reverse cholesterol transport (RCT) was performed whereby radiolabeled cholesterol was delivered to the liver as acetylated LDL and the reappearance of label into plasma and HDL was determined. Plasma radioactivity in TRANS-fed rats was lower than in their SAT-fed counterparts (P = 0.01), and consistent with the cholesterol distribution in plasma, the difference was due to lower [(3)H]-cholesterol in lower density lipoproteins. Despite diet-induced differences in the cholesterol and phospholipid concentrations and fatty acid composition of HDL, the amount of label in HDL did not differ among groups, suggesting that consumption of these diets resulted in HDL populations with similar capacity to participate in RCT. The present findings suggest that dietary trans fatty acids regulate the metabolism of apolipoprotein B-containing lipoproteins in rats and that the effect may be masked in species possessing high plasma cholesteryl ester transfer protein (CETP) activity. These results reinforce the important role of CETP activity in determining the distribution of plasma cholesterol in response to dietary trans fatty acids.

Fatty acid saturation of the diet and plasma lipid concentrations, lipoprotein particle concentrations, and cholesterol efflux capacity

BACKGROUND

The fatty acid content and saturation degree of the diet can modulate HDL composition and cholesterol efflux.

OBJECTIVE

We studied the modifications in plasma lipoprotein particles and serum capacity to stimulate cholesterol efflux induced by different fatty acids.

DESIGN

Seventeen women and 24 men followed in the same sequence 4 diets containing 35% of total energy as fat. The saturated fat diet contained 17% palm oil; the monounsaturated fat diet, 20.9% olive oil; the n-6 polyunsaturated fat diet, 12.5% sunflower oil; and the n-3 polyunsaturated fat diet, sunflower oil supplemented with 4-4.5 g fish oil/d. Each phase lasted 4-5 wk.

RESULTS

In both sexes, apolipoprotein (apo) A-I concentrations were significantly lower with unsaturated fat diets than with the saturated fat diet, but concentrations of lipoproteins containing only apo A-I (Lp A-I) were lower only in the men. Concentrations of lipoproteins containing both apo A-I and apo A-II (Lp A-I:A-II) were lower with both polyunsaturated fat diets in the women but significantly higher in the men. Lp E concentrations were significantly higher with the 2 polyunsaturated fat diets. Lp E non-B particle concentrations were not modified in the men but were significantly higher in the women in both polyunsaturated fat phases. Lp C-III concentrations were higher with the saturated fat diet only in the men. The serum samples taken after the n-3 polyunsaturated fat phase were the most efficient for extracting cellular cholesterol in both sexes.

CONCLUSIONS

The monounsaturated and polyunsaturated fat diets were healthier, producing a better lipid profile. The n-3 polyunsaturated fat diet increased the capacity of serum to promote the efflux of cholesterol from cells in culture.

Cholesterol efflux capacity in vitro predicts the severity and extent of coronary artery disease in patients with and without type 2 diabetes

OBJECTIVE

To investigate the relation between severity and extent of coronary artery disease (CAD) and in vitro cholesterol efflux capacity.

DESIGN

This study consisted of 46 type 2 diabetic, and 42 nondiabetic men undergoing coronary angiography. Quantitative coronary angiography was used to estimate the severity, extent, and overall "atheroma burden" of CAD. The capacity of patient plasma to induce cholesterol efflux from cultured Fu5AH rat hepatoma cells was measured in vitro.

RESULTS

In the combined study population (n = 88), there was a significant inverse correlation between efflux and global atheroma burden (r = -0.23, p < 0.05). In the diabetic group, the global atheroma burden index was independently associated both with cholesterol efflux and with LpA-I levels. However, in the nondiabetic CAD group this association was lost when efflux and LpA-I levels were included in the same model.

CONCLUSION

The present study demonstrated that efflux capacity was inversely associated with the severity and extent of CAD. In the diabetic group this association was independent of LpA-I levels, suggesting impaired antiatherogenic potential of these particles in type 2 diabetic patients.