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The objective of this study was to investigate the effect of individual PUFAs on LDL receptor (LDLr) expression in human fibroblasts and HepG2 cells, and to evaluate whether acyl CoA:cholesterol acyltransferase (ACAT) and sterol regulatory element-binding protein 1 (SREBP-1) were involved in the regulation of LDLr expression by fatty acids. When fibroblasts and HepG2 cells were cultured with serum-free defined medium for 48 h, there was a 3- to 5-fold (P < 0.05) increase in LDLr protein and mRNA levels. Incubation of fibroblasts and HepG2 cells in serum-free medium supplemented with 25-hydroxycholesterol (25OH-cholesterol, 5 mg/L) for 24 h decreased LDLr protein and mRNA levels by 50-90% (P < 0.05). Arachidonic acid [AA, 20:4(n-6)], EPA [20:5(n-3)], and DHA [22:6(n-3)] antagonized the depression of LDLr gene expression by 25OH-cholesterol and increased LDLr protein abundance 1- to 3-fold (P < 0.05), but had no significant effects on LDLr mRNA levels. Oleic (18:1), linoleic (18:2), and [alpha]-linolenic acids [18:3(n-3)] did not significantly affect LDLr expression. ACAT inhibitor (58-035, 1 mg/L) attenuated the regulatory effect of AA on LDLr protein abundance by ~40% (P < 0.05), but did not modify the regulatory effects of other unsaturated fatty acids in HepG2 cells. The present results suggest that AA, EPA, and DHA increase LDLr protein levels, and that ACAT plays a role in modulating the effects of AA on LDLr protein levels. Furthermore, the effects of the fatty acids appeared to be independent of any change in SREBP-1 protein. KEY WORDS: * fatty acids * LDL receptor protein * LDL receptor mRNA

Recent evidence suggests that individuals with high concentrations of C-reactive protein (CRP), a marker of inflammation, are less responsive to cholesterol-lowering diets. CRP concentrations are increased by oral estrogen; however, the effect of soy phytoestrogens on inflammation has not been studied comprehensively, especially in women receiving hormone replacement therapy (HRT). This study was conducted to determine whether adding soy to a low-fat, high-fiber diet affects CRP and interleukin (IL)-6, and to examine the association between CRP levels and lipid response in moderately hypercholesterolemic adults (men = 18, postmenopausal women = 14; 6 receiving HRT). After a 3-wk run-in period with consumption of a Step I diet (27% total fat, 7% saturated fat, 275 mg cholesterol), participants were randomly assigned to diets containing 25 g/d soy protein (+ 90 mg/d isoflavones) or 25 g/d milk protein for 6 wk in a crossover design. Lipids and lipoproteins, CRP, and IL-6 were measured at the end of each diet and participants were categorized into high (>3.5 mg/L) or low CRP groups based on a median split. The addition of soy or milk protein to the Step I diet did not affect lipids or inflammatory markers. Regardless of protein source, those with low CRP exhibited significant decreases in LDL cholesterol (-3.5%) and the LDL:HDL cholesterol ratio (-4.8%), whereas those with high CRP had significant increases in LDL cholesterol (+4.8%), the LDL:HDL cholesterol ratio (+5.2%), apolipoprotein B (+3.8%), and lipoprotein(a) (+13.5%) compared with the run-in diet. These results suggest that inflammation may not only attenuate lipid responses, but also aggravate dyslipidemia in hypercholesterolemic subjects consuming a cholesterol-lowering diet. KEY WORDS: * inflammation * cholesterol * diet * isoflavones * hormone replacement therapy

[alpha]-Linolenic acid (ALA) reduces cardiovascular disease (CVD) risk, possibly by favorably changing vascular inflammation and endothelial dysfunction. Inflammatory markers and lipids and lipoproteins were assessed in hypercholesterolemic subjects (n = 23) fed 2 diets low in saturated fat and cholesterol, and high in PUFA varying in ALA (ALA Diet) and linoleic acid (LA Diet) compared with an average American diet (AAD). The ALA Diet provided 17% energy from PUFA (10.5% LA; 6.5% ALA); the LA Diet provided 16.4% energy from PUFA (12.6% LA; 3.6%,ALA); and the AAD provided 8.7% energy from PUFA (7.7% LA; 0.8% ALA). The ALA Diet decreased C-reactive protein (CRP, P < 0.01), whereas the LA Diet tended to decrease CRP (P = 0.08). Although the 2 high-PUFA diets similarly decreased intercellular cell adhesion molecule-1 vs. AAD (-19.1% by the ALA Diet, P < 0.01; - 11.0% by the LA Diet, P < 0.01), the ALA Diet decreased vascular cell adhesion molecule-1 (VCAM-1, -15.6% vs. -3.1%, P < 0.01) and E-selectin (-14.6% vs. -8.1%, P < 0.01) more than the LA Diet. Changes in CRP and VCAM-1 were inversely associated with changes in serum eicosapentaenoic acid (EPA) (r = -0.496, P = 0.016; r = -0.418, P = 0.047), or EPA plus docosapentaenoic acid (r = -0.409, P = 0.053; r = -0.357, P = 0.091) after subjects consumed the ALA Diet. The 2 high-PUFA diets decreased serum total cholesterol, LDL cholesterol and triglycerides similarly (P < 0.05); the ALA Diet decreased HDL cholesterol and apolipoprotein Al compared with the AAD (P < 0.05). ALA appears to decrease CVD risk by inhibiting vascular inflammation and endothelial activation beyond its lipid-lowering effects. KEY WORDS: * [alpha]-linolenic acid * PUFA * C-reactive protein * cell adhesion molecules * lipids and lipoproteins

Elevated iron stores may or may not promote atherogenesis by increasing free radical formation and oxidative stress, but controlled diet and supplement trials are lacking. We tested the hypothesis that iron supplementation does not increase the susceptibility of LDL to undergo oxidative modification in women with low iron status. A randomized, double-blind, 2-period crossover study design (n = 26) was used to examine the effects of the following diets on measures of LDL oxidation: average American diet (AAD) [36% of energy as fat; 15% saturated fatty acids (SFA)], and a Step 2 diet (26% fat; 7% SFA). In addition, subjects received either a supplement containing 160 mg of ferrous sulfate (50 mg elemental iron) or a placebo twice daily [supplement group received a total of 320 mg ferrous sulfate (100 mg elemental iron) daily]. After supplementation, serum ferritin differed between the supplement and placebo groups (P = 0.008). Measures of LDL oxidation were not affected by supplement intake; however, they were affected by diet. Lag time was shorter after the women consumed the AAD diet than after the Step 2 diet (P < 0.0001). The diets did not affect the rate of oxidation or total dienes. Although iron status was improved by aggressive iron supplementation, LDL oxidative susceptibility was not affected. As expected, lag time was increased after the women consumed the low fat, low SFA diet. Therefore, the results of this study do not support a relationship between iron status and LDL oxidation. KEY WORDS: * LDL oxidation * lag time * iron * ferritin * dietary fat

Conjugated linoleic acid (CLA) exerts anticarcinogenic and antiatherosclerotic effects in animals. The present study was conducted to examine the effects of CLA on LDL receptor (LDLr) expression in HepG2 cells, and to evaluate whether the sterol response element binding protein 1 (SREBP-1) and acyl CoA:cholesterol acyltransferase (ACAT) were involved in the regulation of LDLr expression by CLA. When HepG2 cells were cultured with serum-free DMEM for 48 h, there was a three- to fivefold (P < 0.05) increase in LDLr protein and mRNA levels. Incubation of HepG2 cells in serum-free medium supplemented with 25-hydroxycholesterol (25OH, 5 mg/L) for 24 h decreased LDLr protein and mRNA by 50-70% (P < 0.05) and mature SREBP-1 by 20-40% (P < 0.05). CLA, but not linoleic acid, antagonized the depressive effects of 25OH and increased both LDLr protein and mRNA abundance twofold (P < 0.05). LDLr protein and mRNA abundance were not different when HepG2 cells were cultured with CLA (0.4 mmol/L) plus 25OH in the presence or absence of an ACAT inhibitor (58-035, 1 mg/L). Furthermore, CLA had no effect on SREBP-1 abundance. These results suggest that CLA upregulates LDLr expression via a mechanism that is independent of ACAT and SREBP-1. KEY WORDS: * cholesterol * conjugated linoleic acid * LDL * LDL receptor mRNA * LDL receptor protein

Compared with other saturated fatty acids, stearic acid appears to have different metabolic effects with respect to its impact on risk for cardiovascular disease. These differences may in part reflect biologically important differences in absorption. This study was designed to compare the absorption and the metabolizable energy value of stearic acid with other fatty acids from mixed diets fed to healthy humans. Healthy men (n = 11) were fed four diets with multiple fat sources that contained ~15% of energy (en%) from protein, 46 en% from carbohydrate and 39 en% from fat with 8 en% substitution across diets of the following: trans monoenes, oleic acid, saturated fatty acids (lauric + myristic + palmitic) or stearic acid fed as triacylglycerides. Fats were incorporated into mixed diets comprised of foods typically consumed in the United States. After a 14-d adaptation period, volunteers collected all feces for 7 d. Across diets, absorption of stearic acid (94.1 [+ or -] 0.2%) was lower (P < 0.0002) than that of palmitic acid (97.3 [+ or -] 0.2%) and higher than generally reported. Absorption of lauric, myristic, oleic, linoleic and trans 18:1 monoenes did not differ from each other (>99%) but was higher than that of stearic and palmitic acids (P < 0.001). Metabolizable energy values were similar for all fatty acids. Although absorption of palmitic and stearic acids was affected by diet treatment, the magnitudes of the differences were small and do not appear to be biologically important, at least in terms of lipoprotein metabolism. On the basis of these results, reduced stearic acid absorption does not appear to be responsible for the differences in plasma lipoprotein responses to stearic acid relative to other saturated or unsaturated fatty acids. KEY WORDS: * absorption * metabolizable energy * fatty acids * stearic acid * trans fatty acids

Monounsaturated fatty acids may help prevent cardiovascular disease. These fatty acids have one double bond. Diabetics especially can benefit from a diet high in these fatty acids.

Soy protein with isoflavones has been suggested for lipid lowering in men and women with high cholesterol, in part because of the beneficial effects of pharmaceutical estrogens. However, it is not known whether soy supplements with phytoestrogens enhance the effects of a low-fat diet or whether women on hormone replacement therapy (HRT+, n = 6) show the same benefits from dietary change as unmedicated postmenopausal women (HRT-, n = 12) and age-matched men (n = 15). We conducted a controlled feeding study that included a Step I diet (3 wk), a low-fat diet with 25 g soy protein and 90 mg isoflavones per day (6 wk), and a matched control diet with 25 g casein per day (6 wk). Subjects were their own control in this crossover design. As expected, HRT+ women exhibited significantly higher HDL cholesterol than did HRT- women and men (62, 54, and 48 mg/dL [1.61, 1.40, and 1.24 mmol/L, respectively]; P = 0.04) at study entry; therefore all analyses used pretreatment level as the covariate. In HRT- women and men only, the low-fat diets were associated with significant decreases in LDL cholesterol (average change = -30 [+ or -] 5 mg/dL [-0.78 [+ or -] 0.13 mmol/L]), total cholesterol (-42 [+ or -] 7 mg/dL [-1.09 [+ or -] 0.18 mmol/L]), and HDL cholesterol (-8 [+ or -] 3 mg/dL [-0.21 [+ or -] 0.08 retool/L]) relative to pretreatment values. These effects were not enhanced by soy, and there was no significant effect of protein type for any variable. In contrast, HRT+ women showed no significant changes in LDL, total, or HDL cholesterol during any of the dietary interventions. It is interesting that HRT is associated with preservation of HDL levels even in the presence of low dietary fat intake. This may illustrate a mechanism for the cardioprotective effects of HRT. However, the lack of LDL response in HRT+ subjects may be a result of selection bias by prescribers of HRT: they represent a group with particularly difficult to treat hypercholesterolemia and are good candidates for hormone therapy.