Oleic acid inhibits endothelial activation : A direct vascular antiatherogenic mechanism of a nutritional component in the mediterranean diet

Lipid metabolism in human endothelial cells

Although lipids are largely involved in cardiovascular physiopathology, the lipid metabolism in endothelial cells remains largely unknown. Human umbilical vein endothelial cells (HUVECs) were used to investigate the metabolism of complex lipids. The membrane phospholipid homeostasis results from both de novo synthesis and remodelling that ensures the fine tuning of the phospholipid fatty acid composition. Using [(3)H]-glycerol and phosphoderivatives we showed the efficiency of glycerolipid synthesis from glycerol (0.9 nmol h(-1) mg proteins(-1)), but not from its phosphorylated form suggesting the requirement of a functional glycerol kinase in HUVECs. Conversely, the synthesis of triacylglycerols was very low (less than 5% of phospholipid synthesis). The incorporation rate of fatty acids into phospholipids showed that there is a specific fate for each fatty acid in respect to its chain length and saturation level. Moreover in steady state condition, increasing the long chain omega3 polyunsaturated fatty acids in the medium resulted in an increased polyunsaturated/saturated ratio in phospholipids (from 0.42 to 0.63). [(14)C]O(2) was produced form either [(14)C]-glucose or [(14)C]-palmitate indicating the functionality of the oxidation pathways, although beta-oxidation was less efficient than glucose oxidation. The endothelial cell lipid metabolism involves conventional pathways, with functional rates largely slower than in hepatocytes or in cardiomyocytes.

Inflammatory effects of very low-density lipoprotein and fatty acids

High plasma triacylglycerol (triglyceride, TG) levels is a risk factor for atherosclerosis. Very large lipoproteins, such as chylomicrons, alone are not considered atherogenic, but TG-rich remnant lipoproteins can penetrate into the vascular wall. Importantly, accumulating evidence suggests that all TG-rich lipoproteins stimulate cytokine expression in circulating monocytes. Very low-density lipoprotein (VLDL) stimulates monocyte adhesion to endothelial cells and expression of inflammatory genes in macrophages. Furthermore, fatty acids released from large lipoproteins can stimulate both vascular cells and circulating monocytes. It is likely that fatty acids released from TG-rich lipoproteins contribute to atherogenesis, but the role of fatty acids in ischemic heart disease is not as direct as that of cholesterol. Fatty acids influence plasma lipoprotein levels and either stimulate or suppress numerous cellular functions relevant to atherogenesis. While certain n-3 fatty acids are good for health, most other medium- to long-chain fatty acids appear to promote inflammation in cell culture studies and need to be studied further. Nevertheless, the existing evidence supports the general conclusion that TG-rich lipoproteins and fatty acids greatly accelerate the progression of atherosclerosis. This may be because of their inflammatory effects.

Mediterranean-inspired diet lowers the ratio of serum phospholipid n-6 to n-3 fatty acids, the number of leukocytes and platelets, and vascular endothelial growth factor in healthy subjects

BACKGROUND

Reduced cardiovascular mortality and morbidity have been shown in persons adhering to Mediterranean-inspired diets (MIDs). Although the underlying mechanisms of this association are poorly understood, the importance of increasing dietary amounts of polyunsaturated fatty acids of the n-3 series has been emphasized.

OBJECTIVE

We investigated whether a MID provided to healthy subjects would affect 1) the inflammatory process and endothelial indexes such as vasoregulation and vascular endothelial growth factor (VEGF) and 2) serum phospholipid fatty acid composition.

DESIGN

A total of 22 subjects (10 women) received a MID or an ordinary Swedish diet (OSD) for 4 wk in a crossover fashion. Concentrations of lipids and fatty acids, high-sensitivity C-reactive protein, and interleukin 6, both before and after lipopolysaccharide stimulation; the number of leukocytes and platelets; and VEGF and monocyte chemoattractant protein 1 were analyzed.

RESULTS

The plasma ratio of n-6 to n-3 fatty acids was substantially lower after the MID than after the OSD (x +/- SEM: 4.72 +/- 0.19 and 2.60 +/- 0.17, respectively; P < 0.0001). Neither C-reactive protein nor interleukin 6 concentrations changed significantly after the MID compared with the OSD. The total number of leukocytes and platelets was 10% (P < 0.05) and 15% (P < 0.001) lower, respectively, after the MID than after the OSD. Serum VEGF concentrations were lower after the MID than after the OSD (237 +/- 30 and 206 +/- 25 pg/mL, respectively; P = 0.0014).

CONCLUSIONS

A MID reduces the number of platelets and leukocytes and VEGF concentrations in healthy subjects. This may be linked to higher serum concentrations of n-3 fatty acids, which promote a favorable composition of phospholipids.

Suppression of vascular cell adhesion molecule-1 expression by crocetin contributes to attenuation of atherosclerosis in hypercholesterolemic rabbits

To elucidate the molecular mechanism by which antioxidants alleviate atherosclerosis, we investigated the effect of crocetin, a naturally occurred carotinoid with potent antioxidant power, on vascular cell adhesion molecule-1 (VCAM-1) expression in atherosclerotic rabbits. Twenty-four male New Zealand White rabbits were allocated to three groups fed on standard diet (control group), high lipid diet (HLD group) or high lipid diet supplemented with crocetin (crocetin group), respectively. After 8 weeks of treatment, rabbits in HLD group developed severe hypercholesterolemia and atherosclerosis in aortas, together with a significantly up-regulated expression of both protein and mRNA for VCAM-1. In contrast, supplementation with crocetin resulted in markedly ameliorated atherosclerosis, coupled with a significantly decreased VCAM-1 expression, though plasma lipids level remained comparable to that of HLD group. Regression analysis revealed a positive correlation between VCAM-1 expression and the extent of atherosclerosis (P < 0.01). In addition, immunohistochemical analysis showed an increased activation of nuclear factor kappa B (NF-kappaB), a redox sensitive transcription factor essential for VCAM-1 expression, in aortas from rabbits fed on high lipid diet, which was evidently suppressed by crocetin supplementation. These findings suggest that the antiatherosclerotic effect of crocetin might be attributed, at least in part, to the suppressed expression of VCAM-1, which might result from reduced NF-kappaB activation. This study provides a further insight into the molecular mechanism by which antioxidants attenuate atherosclerosis and suggests a potential target for the treatment of atherosclerosis with antioxidants.

Anti-inflammatory effects of polyunsaturated fatty acids in THP-1 cells

The effects of linoleic acid (LA), alpha-linolenic acid (ALA), and docosahexaenoic acid (DHA) were compared to that of palmitic acid (PA), on inflammatory responses in human monocytic THP-1 cells. When cells were pre-incubated with fatty acids for 2-h and then stimulated with lipopolysaccharide for 24-h in the presence of fatty acids, secretion of interleukin (IL)-6, IL-1beta, and tumor necrosis factor-alpha (TNFalpha) was significantly decreased after treatment with LA, ALA, and DHA versus PA (P < 0.01 for all); ALA and DHA elicited more favorable effects. These effects were comparable to those for 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2) and were dose-dependent. In addition, LA, ALA, and DHA decreased IL-6, IL-1beta, and TNFalpha gene expression (P < 0.05 for all) and nuclear factor (NF)-kappaB DNA-binding activity, whereas peroxisome proliferator-activated receptor-gamma (PPARgamma) DNA-binding activity was increased. The results indicate that the anti-inflammatory effects of polyunsaturated fatty acids may be, in part, due to the inhibition of NF-kappaB activation via activation of PPARgamma.

Fibronectin type II (FnII)-like modules regulate gelatinase A activity

Gelatinase A, a member of the matrix metalloproteinase family, contains three fibronectin type II (FnII)-like modules that are inserted within its catalytic domain. These FnII modules, defined as exosites, play an essential role in targeting the enzyme to matrix macromolecules, a process which can down-regulate membrane-type metalloproteinase-driven progelatinase A activation. The exosite/substrate-directed gelatinase inhibitors has been proposed as an alternative approach to disappointing active site-directed inhibitors, to control gelatinase A activity. In preliminary experiments, we evidenced that long-chain unsaturated fatty acids could bind preferentially to the first FnII module of gelatinase A. This interaction inhibits the activity of this enzyme towards proteins (type I gelatin and collagen) and an octapeptide substrate, with K(i) in the micromolar range. Since gelatinase A-catalyzed matrix proteolysis might display a positive or negative influence (depending on the substrate cleaved), the design of exosite-specific compounds for noncatalytic targeting of gelatinase A would necessitate an extensive degradomic analysis.

Omega-3 Fatty Acids and the Regulation of Expression of Endothelial Pro-Atherogenic and Pro-Inflammatory Genes

By partially replacing the corresponding omega-6 analogues in membrane phospholipids, omega-3 fatty acids have been shown to decrease the transcriptional activation of genes--e.g., adhesion molecules, chemoattractants, inflammatory cytokines--involved in endothelial activation in response to inflammatory and pro-atherogenic stimuli. This regulation occurs, at least in part, through a decreased activation of the nuclear factor-kappaB system of transcription factors, secondary to decreased generation of intracellular hydrogen peroxide. Such regulation by omega-3 fatty acids is likely linked to the presence of a higher number of double bonds in the fatty acid chain in omega-3 compared with omega-6 fatty acids. By similar mechanisms, omega-3 fatty acids have been recently shown to reduce gene expression of cyclooxygenase-2, an inflammatory gene involved, through the activation of some metalloproteinases, in plaque angiogenesis and plaque rupture. The quenching of gene expression of pro-inflammatory pro-atherogenic genes by omega-3 fatty acids has consequences on the extent of leukocyte adhesion to vascular endothelium, early atherogenesis and later stages of plaque development and plaque rupture, ultimately yielding a plausible comprehensive explanation for the vasculoprotective effects of these nutrients.

Lack of proinflammatory effects of free fatty acids on human umbilical cord vein endothelial cells and leukocytes

AIM

To determine whether the free fatty acids (FFAs), oleic, linoleic, and palmitic acid, found elevated before 20 weeks of pregnancy in those women who later develop preeclampsia, induced changes in expression of the vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), or E-selectin in cultured human umbilical cord vein endothelial cells (HUVEC), and integrin subunit CD11b, L-selectin or intracellular reactive oxygen species (ROS) in leukocytes.

METHODS

The VCAM-1, ICAM-1, and E-selectin expression were measured using ELISA in HUVEC after incubation with 100 micromol of either oleic, linoleic, or palmitic acid for 6 hr and 24 hr. The co-reactivity with lipopolysaccharide (LPS), the amount of VCAM-1 mRNA in the cells, and soluble VCAM-1 in the incubation medium were measured as well. Leukocyte adhesion molecules and ROS were measured after incubation with 750 microm of either of the FFAs in a whole blood model using flow cytometry.

RESULTS

No effects of the FFAs tested were found on the HUVEC or leukocyte adhesion molecule expression or intracellular ROS. The only exception to this was palmitic acid incubation, which significantly lowered the VCAM-1 expression in HUVEC after 24-hr incubation and also slowed the decay of VCAM-1 expressed after stimulation with LPS.

CONCLUSIONS

The lack of significant proinflammatory changes of the FFAs tested might indicate that the elevated plasma levels of FFAs seen in preeclampsia most probably are products of the preeclamptic process rather than a causative factor.

Contrasting effect of fish oil supplementation on the development of atherosclerosis in murine models

OBJECTIVE

Increased fish oil intake is associated with protection against coronary heart disease and sudden death, while effects on atherosclerosis are controversial. We explored the effects of supplementing fish oil (rich in n-3 polyunsaturated fatty acids, PUFA) or corn oil (rich in n-6 PUFA) in two different models of atherosclerosis.

METHODS AND RESULTS

Sixty-three low density lipoprotein receptor-deficient (LDLR(-/-)) mice and sixty-nine apolipoprotein E-deficient (apoE(-/-)) mice were fed diets without supplementations or supplemented with either 1% fish oil or 1% corn oil. In apoE(-/-) mice, neither fish oil nor corn oil had any major impact on plasma lipids or atherosclerosis. In LDLR(-/-) mice, conversely, the fish oil and the corn oil group had lower levels of LDL-cholesterol and triglycerides and had lesser atherosclerosis in the aortic root and in the entire aorta (p < 0.01 versus unsupplemented group). Atherosclerosis was significantly less in the fish oil group compared with the corn oil group when evaluated en face in the aortic arch (area positive to lipid staining: 32% with fish oil versus 38% with corn oil; 48% with unsupplemented diet).

CONCLUSIONS

n-3 and n-6 PUFA supplementation retarded the development of atherosclerosis in LDLR(-/-) mice, with a stronger effect seen with n-3 PUFA. There was an important strain-dependence of the effect, with no protection against atherosclerosis in apoE(-/-) mice.

Palmitate-induced interleukin-6 expression in human coronary artery endothelial cells

Obesity-linked insulin resistance is associated with chronic inflammation and cardiovascular complications. Free fatty acids (FFAs) are prominent candidates for the molecular link between these disorders. In this study, we determined whether FFAs contribute to vascular inflammation via induction of interleukin (IL)-6 in coronary artery endothelial cells (CAECs) and coronary artery smooth muscle cells (CASMCs) and whether this is reflected in vivo. In contrast to our findings regarding IL-6 and gp130 (the glycoprotein of 130 kDa) expression, IL-6 receptor mRNA expression was very low in these cells. Palmitate, but not linoleate, induced a significant increase in IL-6 mRNA expression in CAECs (P < 0.001) and, to a less relevant extent, in CASMCs (P < 0.01). gp130 remained unaffected. As to potency, palmitate was comparable with the IL-6-inducer IL-1beta. To substantiate our in vitro data, we examined the plasma FFA pattern in 54 healthy human subjects and studied the relation of individual FFAs with plasma IL-6. IL-6 levels correlated with palmitate, but not with other abundant FFAs, even after adjusting for body fat (r = 0.33, P < 0.05) and total FFAs (r = 0.29, P < 0.05). We show here that the common plasma FFA palmitate induces high levels of IL-6 in CAECs. Furthermore, palmitate correlates with IL-6 in vivo. This points to a potential contribution of palmitate to vascular inflammation.

A Mediterranean dietary style influences TNF-alpha and VCAM-1 coronary blood levels in unstable angina patients

BACKGROUND

A Mediterranean dietary pattern has been associated with a reduced risk of coronary heart disease, as well as a reduction of oxidative stress, but studies indicating possible interactions between food intake and inflammatory mediators production at specific sites are lacking.

AIM OF THE STUDY

To assess the relationship between Mediterranean diet consumption and inflammatory related molecules production in coronary vessels.

METHODS

A previously reported Mediterranean-diet score was computed summing-up the quintiles of eight dietary components from a validated food frequency questionnaire in 24 patients with unstable angina. Tumor necrosis factor (TNF-alpha) and vascular cell adhesion molecule (VCAM-1) concentrations were measured in coronary sinus blood.

RESULTS

Both biomarkers showed an inverse association with the Mediterraneandiet score. The association between VCAM-1 and the Mediterranean-diet score had an adjusted beta coefficient of -35.1 ng/ml (95% coefficient interval, CI: -63.5 to -6.7). The adjusted beta coefficient using TNF-alpha as the dependent variable was -41.6 pg/ml (95 % CI: -76.2 to -7.1). The consumption of olive oil as a single item showed a significant inverse association, and a Mediterranean-diet score excluding olive oil was also inversely associated with TNF-alpha and VCAM-1 serum levels in coronary venous blood.

CONCLUSIONS

Adherence to a Mediterranean dietary pattern may protect against coronary artery wall production of inflammatory mediators. This finding could provide a novel mechanistic explanation for the recognized lower coronary risk associated with a Mediterranean diet.

Effects of omega-3 fatty acids on cytokines and adhesion molecules

The dietary intake of omega-3 (n-3) polyunsaturated fatty acids has emerged, over the past 20 years, as an important way to modify cardiovascular risk. This likely occurs through beneficial effects at all stages in the natural history of vascular disease, from the inception of atherosclerotic lesions, to their growth and acute complications (plaque rupture in most instances), up to protection of myocardium from the consequences of ensuing acute myocardial ischemia. This review specifically focuses on the modulating effects of n-3 fatty acids on biologic events involved in early atherogenesis, including important properties of these natural substances on endothelial expression of adhesion molecules and cytokines, processes collectively denoted as "endothelial activation." By decreasing the endothelial responsiveness to proinflammatory and proatherogenic stimuli, n-3 fatty acids act on molecular events not targeted by any other drugs or interventions, and thereby complementary to those of already implemented pharmacologic treatments.

Dietary alpha-linolenic acid reduces inflammatory and lipid cardiovascular risk factors in hypercholesterolemic men and women

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 AI 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.

Effect of pulmonary surfactant on TNF-α-activated endothelial cells and neutrophil adhesion in vitro

Pulmonary surfactant given to infants and adults with respiratory failure is metabolized and recycled to a large extent. A small proportion also enters the circulation in cases of increased permeability of the alveolar-capillary membrane. We therefore investigated whether exogenous surfactants such as a natural bovine (natSF) or a synthetic (synSF) preparation had an impact on inflammatory conditions involving the adhesion of neutrophils to endothelial cells. Human umbilical cord vein endothelial cells (HUVEC) were plated on coverslips until confluence, activated by tumor necrosis factor-alpha and incubated with or without surfactant in the media. Human neutrophils passed the HUVEC layer in a flow chamber and interactions were visualized using a video microscope. To test if surfactant affected the expression of cell adhesion molecules, RT-PCR analyses were performed for E-selectin, vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1). Using concentrations between 50 and 300 microg/ml of surfactant in the pre-incubation media the number of adherent neutrophils increased by 10-20% at the higher concentration of the natSF (*P < 0.05) whereas the synSF had no effect. Increased neutrophil adhesion was associated with a significant up-regulation of mRNA levels for E-selectin and VCAM-1; mRNA levels for ICAM-1, however, were not affected by the presence of surfactant. These observations indicate that natSF but not synSF might have pro-inflammatory effects when higher amounts of the exogenous dose reach the circulation. This might be explained by different fatty acid profiles, e.g. the presence of arachidonic acid in the natSF or higher concentrations of surfactant-associated protein-C in the synSF.

Decreased aortic early atherosclerosis and associated risk factors in hypercholesterolemic hamsters fed a high- or mid-oleic acid oil compared to a high-linoleic acid oil

Currently, diets higher in polyunsaturated fat are believed to lower blood cholesterol concentrations, and thus reduce atherosclerosis, greater than diets containing high amounts of saturated or possibly even monounsaturated fat. The present study was designed to investigate the effect of diets containing mid- or high-linoleic oil versus the typical high-linoleic sunflower oil on LDL oxidation and the development of early atherosclerosis in a hypercholesterolemic hamster model. Animals were fed a hypercholesterolemic diet containing 10% mid-oleic sunflower oil, high-oleic olive oil, or high-linoleic sunflower oil (wt/wt) plus 0.4% cholesterol (wt/wt) for 10 weeks. After 10 weeks of dietary treatment, only the animals fed the mid-oleic sunflower oil had significant reductions in plasma LDL-C levels (-17%) compared to the high-linoleic sunflower oil group. The high-oleic olive oil-fed hamsters had significantly higher plasma triglyceride levels (+41%) compared to the high-linoleic sunflower oil-fed hamsters. The tocopherol levels in plasma LDL were significantly higher in hamsters fed the mid-oleic sunflower oil (+77%) compared to hamsters fed either the high-linoleic sunflower or high-oleic olive oil. Measurements of LDL oxidation parameters, indicated that hamsters fed the mid-oleic sunflower oil and high-oleic olive oil diets had significantly longer lag phase (+66% and +145%, respectively) and significantly lower propagation rates (-26% and -44%, respectively) and conjugated dienes formed (-17% and -25%, respectively) compared to the hamsters fed the high-linoleic sunflower oil. Relative to the high-linoleic sunflower oil, aortic cholesterol ester was reduced by -14% and -34% in the mid-oleic sunflower oil and high-oleic olive oil groups, respectively, with the latter reaching statistical significance. Although there were no significant associations between plasma lipids and lipoprotein cholesterol with aortic total cholesterol and cholesterol esters for any of the groups, the lag phase of conjugated diene formation was inversely associated with both aortic total and esterified cholesterol in the high-oleic olive oil-fed hamsters (r = -0.69, P < 0.05). The present study suggests that mid-oleic sunflower oil reduces risk factors such as lipoprotein cholesterol and oxidative stress associated with early atherosclerosis greater than the typical high-linoleic sunflower oil in hypercholesterolemic hamsters. The high-oleic olive oil not only significantly reduced oxidative stress but also reduced aortic cholesterol ester, a hallmark of early aortic atherosclerosis greater than the typical high-linoleic sunflower oil.

Serum fatty acid composition in primary school children is associated with serum cholesterol levels and dietary fat intake

OBJECTIVE

To examine the serum fatty acid composition, serum cholesterol levels, and dietary fat intake associated with body composition in primary school children of both urban and rural regions in Taiwan.

DESIGN

Subjects were randomly stratified by region and primary school. The sample consisted of 870 children aged 10 and 11 y old. The sample was equally distributed between an urban region (Kaohsiung City) and a rural region (Yunlin County). The gender ratio of samples from each area was matched. Food record-assisted 24-h dietary recalls and serum lipid measurements were collected for each child, and associations between serum total cholesterol (TC) and fatty acids composition as well as between body mass index (BMI) and triceps skinfold (TSF) were evaluated for both urban and rural regions.

RESULTS

Compared with students in the urban region, those in the rural region had significantly lower total fat intake, BMI, TSF, TC, and LDL cholesterol (LDL-C) and higher HDL-cholesterol (HDL-C) (P<0.05). Increased total fat (P<0.05) as a proportion of total energy was associated with increased TC and LDL-C. Lauric, myristic, and oleic acid levels in the serum of urban boys were significantly higher (P=0.0001, 0.0003, and 0.0398, respectively) than those of rural boys. In girls, the different fatty acid compositions affected TC concentrations, and palmitic and stearic acids of serum in the high-TC group were significantly lower (P=0.0179 and 0.0001, respectively) than those in the low-TC group.

CONCLUSIONS

Urban children had a dietary fat intake that both quantitatively and qualitatively differed from the traditional rural Chinese diet in Taiwan as reflected in rural children. Consumption of total fat was positively associated with BMI, TSF, TC, and LDL-C levels in Taiwanese children aged 10 and 11 y.

SPONSORSHIP

This study was partly sponsored by a research grant from the Department of Health, Taiwan, ROC.

Free fatty acids trigger apoptosis and inhibit cell cycle progression in human vascular endothelial cells

Plasma free fatty acid (FFA) concentrations are increased in states of insulin resistance and impair endothelial function. Because the underlying mechanisms are largely unknown, we examined selected, purified FFAs' (100-300 micromol/l, 24-48 h) action on apoptosis, cell cycle distribution, and associated gene/protein expression in human umbilical vein endothelial cells (HUVECs). Stearic acid, but not oleic acid, time and concentration dependently increased endothelial apoptosis by fivefold (n=6, P<0.01), whereas polyunsaturated FFAs (PUFAs; linoleic, gamma-linolenic, and arachidonic acid) exerted proapoptotic activity only at 300 micromol/l (P<0.05). Proapoptotic FFA action increased with FFAs' number of double bonds and with protein expression of the apoptosis promotor bak. The G0/G1 cell cycle arrest (n=6, P<0.05) induced by stearic acid (+14%) and PUFAs (+30%) is reflected by up-regulation of p21(WAF-1/Cip1). In addition, all FFAs concentration dependently reduced (P<0.05) gene/protein expression of clusterin (-54%), NF-kappaB's inhibitor, IkappaBalpha (-50%), endothelin-1 (-44%), and endothelial NO synthase (-44%). Plasma samples obtained from individuals with elevated plasma FFAs (372+/-22 micromol/l) increased endothelial apoptosis by 4.2-fold (P<0.001, n=10) compared with intra-individually matched low plasma FFA (56+/-21 micromol/l) conditions, underlining the results obtained by defined FFA stimulation. In conclusion, FFA structure differently affects endothelial cell proliferation and apoptosis, both representing key factors in the development of micro- and macrovascular dysfunction.

Dietary cis-monounsaturated fatty acids and metabolic control in type 2 diabetes

Whether low-fat, high-carbohydrate (CHO) diets or moderately high-fat, high-monounsaturated fatty acid (MUFA) diets are preferable for the treatment and prevention of diabetes has been a matter of debate. High-fat diets based on MUFA-rich oils or whole foods have been compared with high-CHO diets for effects on several cardiovascular risk outcomes in diabetic subjects. Early studies using metabolic diets with wide differences in total fat content (15-25% of energy) generally found a beneficial effect of MUFA diets on glycemic control and serum lipids. Recent studies using prescribed diets with a difference of </= 15% of energy in total fat between low-fat and high-MUFA diets show similar effects on glycemic profiles but still favor MUFA diets for effects on triacylglycerols and HDL cholesterol. It is unclear whether postprandial fat clearance is impaired by CHO diets and improved by MUFA diets, independent of effects on fasting triacylglycerol concentrations. Unless one diet contains abundant antioxidants, the 2 dietary approaches appear to have similar effects on LDL oxidation. Low-fat diets, however, are associated with atherogenic, dense LDL particles, while normal, buoyant LDL predominate with high-fat diets irrespective of fatty acid composition. Limited experimental evidence suggests that MUFA diets favorably influence blood pressure, coagulation, endothelial activation, inflammation, and thermogenic capacity. Energy-controlled high-MUFA diets do not promote weight gain and are more acceptable than low-fat diets for weight loss in obese subjects. Thus, there is good scientific support for MUFA diets as an alternative to low-fat diets for medical nutrition therapy in diabetes.

Dietary factors in atherogenesis

Emerging evidence continues to increase our awareness of the complexity of pathologic processes involved in atherogenesis. Dietary modulation exclusively targeting cholesterol consumption is rapidly becoming an archaic mode of intervention as alternative theories of atherogenesis evolve. The interaction of nutrients that occurs with different dietary patterns has been the subject of intense research. Similarly, the effect of diet on vascular reactivity, lipid metabolic kinetics, and antioxidant potential has enormous implications for therapeutic modalities targeting atherosclerosis. Many dietary strategies aimed at inhibiting and preventing atherogenesis have resulted from ongoing research. Consensus opinions extrapolated from available data have also emerged. Regardless, the precise role of dietary modulation in atherogenesis is yet to be fully elucidated. This article reviews recent evidence relating to the interface between dietary factors and biologic models of atherogenesis. Clinical implications and practical applications are also discussed.

Lipotoxicity: when tissues overeat

PURPOSE OF REVIEW

This review will provide the reader with an update on our understanding of the adverse effects of fatty acid accumulation in non-adipose tissues, a phenomenon known as lipotoxicity. Recent studies will be reviewed. Cellular mechanisms involved in the lipotoxic response will be discussed. Physiologic responses to lipid overload and therapeutic approaches to decreasing lipid accumulation will be discussed, as they add to our understanding of important pathophysiologic mechanisms.

RECENT FINDINGS

Excess lipid accumulation in non-adipose tissues may arise in the setting of high plasma free fatty acids or triglycerides. Alternatively, lipid overload results from mismatch between free fatty acid import and utilization. Evidence from human studies and animal models suggests that lipid accumulation in the heart, skeletal muscle, pancreas, liver, and kidney play an important role in the pathogenesis of heart failure, obesity and diabetes. Excess free fatty acids may impair normal cell signaling, causing cellular dysfunction. In some circumstances, excess free fatty acids induce apoptotic cell death.

SUMMARY

Recent studies provide clues regarding the cellular mechanisms that determine whether excess lipid accumulation is well tolerated or cytotoxic. Critical in this process are physiologic mechanisms for directing excess free fatty acids to specific tissues as well as cellular mechanisms for channeling excess fatty acid to particular metabolic fates. Insight into these mechanisms may contribute to the development of more effective therapies for common human disorders in which lipotoxicity contributes to pathogenesis.

Nutrient involvement in preeclampsia

Preeclampsia is a pregnancy-specific condition that increases maternal and infant mortality and morbidity. It is diagnosed by new-onset increased blood pressure and proteinuria during gestation; for many years these markers were the sole targets for study. More recently, increased attention to the multisystemic nature of the syndrome with involvement of almost all organs, activation of coagulation and increased sensitivity to pressor agents has expanded understanding of the disorder. The epidemiology of preeclampsia, being more common in poor women, long ago suggested that nutrients might be involved in the disorder. Numerous conflicting hypotheses were advanced but the testing of these hypotheses has either been done poorly or not at all. Review of the available data indicates very few studies that provide useful insights. In many studies the syndrome is poorly defined and in most studies nutritional data (questionnaires or biomarkers) are obtained on women with the clinical syndrome. In overtly preeclamptic women it is impossible to decipher cause from effect. Nonetheless, current concepts of the genesis of preeclampsia that include endothelial dysfunction, inflammatory activation, oxidative stress and predisposing maternal factors provide targets for well-designed nutritional investigation. In this review the current concepts of the pathogenesis of preeclampsia are reviewed and available data are assessed in light of these concepts. Targets for nutritional investigation based on the current knowledge of pathophysiology are suggested.

Effects of omega-3 polyunsaturated fatty acids on cardiac sarcolemmal Na(+)/H(+) exchange

Myocardial ischemia-reperfusion activates the Na(+)/H(+) exchanger, which induces arrhythmias, cell damage, and eventually cell death. Inhibition of the exchanger reduces cell damage and lowers the incidence of arrhythmias after ischemia-reperfusion. The omega-3 polyunsaturated fatty acids (PUFAs) are also known to be cardioprotective and antiarrhythmic during ischemia-reperfusion challenge. Some of the action of PUFAs may occur via inhibition of the Na(+)/H(+) exchanger. The purpose of our study was to determine the capacity for selected PUFAs to alter cardiac sarcolemmal (SL) Na(+)/H(+) exchange. Cardiac membranes highly enriched in SL vesicles were exposed to 10-100 microM eicosapentanoic acid (EPA) or docosahexanoic acid (DHA). H(+)-dependent (22)Na(+) uptake was inhibited by 30-50% after treatment with > or =50 microM EPA or > or =25 microM DHA. This was a specific effect of these PUFAs, because 50 microM linoleic acid or linolenic acid had no significant effect on Na(+)/H(+) exchange. The SL vesicles did not exhibit an increase in passive Na(+) efflux after PUFA treatment. In conclusion, EPA and DHA can potently inhibit cardiac SL Na(+)/H(+) exchange at physiologically relevant concentrations. This may explain, in part, their known cardioprotective effects and antiarrhythmic actions during ischemia-reperfusion.

Unsaturated fatty acids and their oxidation products stimulate CD36 gene expression in human macrophages

Fatty acids (FA) have been implicated in the control of expression of several atherosclerosis-related genes. Similarly, the CD36 receptor has recently been shown to play an important role in atherosclerosis and other pathologies. The aim of the present study was to evaluate the direct effect of FA and their oxidation products (aldehydes), on the expression of CD36 in both THP-1 macrophages and human monocyte-derived macrophages (HMDM). The FA tested included the saturated FA (SFA) lauric, myristic, palmitic and stearic acid; the monounsaturated FA oleic acid; and the unsaturated FA (UFA) linoleic, arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Aldehydes used were malondialdehyde (MDA), hexanal, 2,4-decadienal (DDE) and 4-hydroxynonenal (HNE). CD36 expression was measured by RT-PCR, Western blot and immunofluorescence. Incubation of THP-1 macrophages for 24 h with non-cytotoxic concentrations of UFA significantly increased CD36 mRNA expression. By contrast, exposure of THP-1 macrophages to SFA did not affect the levels of CD36 mRNA. Among all UFAs tested, EPA and DHA were the strongest inducers of CD36 mRNA levels, followed by oleic and linoleic acid. Incubation of HMDM with either oleic or linoleic acid significantly increased steady-state CD36 mRNA in a dose-dependent manner. Consistent with the increase of CD36 mRNA expression, incubation of THP-1 macrophages with oleic and linoleic acid for 24 h markedly increased CD36 protein expression. Treatment of THP-1 macrophages with MDA or hexanal for 24 h significantly increased CD36 mRNA expression in a dose dependent manner. In contrast, DDE and HNE significantly decreased this parameter. The data provide evidence for a direct regulatory effect of UFA on CD36 gene expression and support a role for aldehydes in the regulation of CD36 expression by FA.

Different sources of dietary n-6 polyunsaturated fatty acids and their effects on antibody responses in chickens

1. Effects of linoleic and linolenic acid provided via different oil sources on total antibody (Ab) titres, Ab isotypes after primary and secondary immunisation, and cutaneous hypersensitivity (CH) responses to bovine serum albumin (BSA) and maleyl-BSA, respectively, were studied in pullets fed on one of 4 diets. The diets were the basal control diet enriched with either sunflower oil or safflower oil as sources of linoleic acid, and linseed oil as a source of linolenic acid, tested against a control diet supplemented with animal fat. 2. Total Ab and immunoglobulin (Ig) isotype responses to BSA were affected by diet after primary, and diet x immunisation effects after secondary immunisation. Higher total Ab and IgG titres to BSA were found especially after primary immunisation in birds given the sunflower oil enriched diet, whereas birds given sunflower oil mounted significantly lower IgM titres to BSA after primary and secondary immunisation. The antibody responses to maleyl-BSA were affected by diet after primary, and immunisation x diet interactions after secondary immunisation. Sunflower oil enhanced total and IgG Ab titres to maleyl-BSA after primary immunisation, but decreased IgM titres to maleyl-BSA after primary and secondary immunisation. Cutaneous hypersensitivity responses to BSA and maleyl-BSA were not affected by the diet. 3. It is concluded that modulation of the magnitude and isotype of Ab responses of poultry to T cell-dependent antigens is affected not only by type of essential fatty acids, but also by their source. In the present study the n-6 source, sunflower oil, showed strong enhancement of primary Ab responses, directed to both Th2 and Th1 antigens. On the other hand, the different effects of safflower oil imply that constituents other than n-6 acids within dietary plant oils may affect immune responsiveness. 4. The relationship between magnitude and isotype of Ab responsiveness, type of antigen, and essential fatty acids is discussed.

Protective effect of dietary monounsaturated fat on arteriosclerosis: beyond cholesterol

The consumption of diets enriched in monounsaturated fat has been related to a lower rate of coronary heart disease. It is well known that this dietary model decreases LDL-cholesterol plasma levels when replacing a saturated fat enriched diet. For this reason, a high monounsaturated fat diet is now being advocated to prevent cardiovascular disease, especially in Mediterranean countries. However, some expert panels-the Joint Task Force of European and other Societies on Coronary Prevention and the International Task Force for Prevention of Coronary Heart Disease-recommend replacing dietary saturated fat by complex carbohydrates, limiting the intake of total fat to <30% of the energy and monounsaturated fat to no more than 10-15% of total calories, reaching a similar effect on LDL-cholesterol plasma levels to a high monounsaturated fat diet. The most appropriate nutritional model to prevent arteriosclerosis should be supported by research into other biological effects of both diets. Therefore, it is interesting to review the non-lipid effect of monounsaturated fat, starting with its influence on other cardiovascular risk factors, such as carbohydrate metabolism and blood pressure. Moreover, substantial evidence of the effect of dietary monounsaturated fat on a wide range of healthy benefits beyond cholesterol, which have been investigated in recent years, such as lipoprotein oxidation, coagulation, fibrinolysis and endothelium, will be discussed. Furthermore, many observational epidemiological studies suggest that a high intake of monounsaturated fat is associated with reduced coronary risk and this will be analyzed in accordance with the clinical evidence to discuss the best dietary model to prevent coronary artery disease.

Mechanisms for reduction of endothelial activation by oleate: inhibition of nuclear factor-kappaB through antioxidant effects

In a model of early atherogenesis based on cultured endothelial cells, we observed that the incorporation of oleic acid in cellular lipids decreases the stimulated expression of several endothelial adhesion molecules and soluble products typically expressed during endothelial activation and involved in monocyte recruitment. We investigated possible mechanisms for this effect assessing the stimulated induction of nuclear factor-kappaB. In parallel, we also measured glutathione (GSH) content and the activity of antioxidant enzymes after oleate treatment and cytokine stimulation. Oleate prevented the stimulated depletion of GSH without any change in the activity of antioxidant enzymes. These results suggest an antioxidant mechanism by which oleate may exert direct vascular atheroprotective effects.

n-3 fatty acids: antiatherosclerotic effects

The low incidence of cardiovascular disease associated epidemiologically with high consumption of food rich in n-3 fatty acids suggests the possibility that part of the beneficial cardiovascular effects of these natural substances may be due to a reduction of atherosclerosis. This has been recently confirmed in autoptic data and in at least one prospective trial evaluating the progression of coronary atherosclerosis in humans. This paper reviews published literature on n-3 fatty acids and atherosclerosis in animal models and in humans and in vitro experimental data yielding suport to the hypothesis of antiatherosclerotic effects of these substances.

Decreased aortic early atherosclerosis in hypercholesterolemic hamsters fed oleic acid-rich TriSun oil compared to linoleic acid-rich sunflower oil

Previous studies have demonstrated that low density lipoprotein (LDL) enriched in polyunsaturated fatty acids (PUFA) are more susceptible to oxidation (ex vivo) than those containing monounsaturated fatty acids (MUFA). To test whether this observation was associated with various parameters considered to be related with the development of early aortic atherosclerosis, hamsters were fed commercial hypercholesterolemic diets (HCD) containing either the PUFA, sunflower oil (SF) or the MUFA, TriSun oil (TS) at 10% with 0.4% cholesterol (wt/wt). LDL isolated from hamsters fed TS had significantly longer lag phase (30%, P < 0.05), a decreased propagation phase (-62%, P < 0.005), and fewer conjugated dienes formed (-37%, P < 0.007) compared to hamsters fed SF. Aortic vasomotor function, measured as degree of aortic relaxation, was significantly greater in the TS vs SF-fed hamsters whether acetylcholine or the calcium ionophore A23187 was used as the endothelium-dependent agonist. As a group, the SF-fed hamsters had significantly more early atherosclerosis than hamsters fed TS (46%, P < 0.006). When animals across the two diets were pair-matched by plasma LDL-C levels, there was an 82% greater mean difference (P < 0.002) in early atherosclerosis in the SF versus the TS-fed hamsters. While there were no significant associations with plasma lipids and lipoprotein cholesterol, early atherosclerosis was significantly correlated with lag phase (r = -0.67, p < 0.02), rate of LDL conjugated diene formation (r = 0.74, p < 0.006) and maximum dienes formed (r = 0.67, p < 0.02). Compared to TS-fed animals, aortic sections from hamsters fed the SF-containing diet revealed that the cytoplasm of numerous foam cells in the subendothelial space reacted positively with the monoclonal anti-bodies MDA-2 and NA59 antibody, epitopes found on oxidized forms of LDL. The present study suggests that compared to TS, hamsters fed the SF-diet demonstrated enhanced LDL oxidative susceptibility, reduced aortic relaxation, greater early aortic atherosclerosis and accumulation of epitopes found on oxidized forms of LDL.

Prevention of postcoronary angioplasty restenosis by omega-3 fatty acids: main results of the Esapent for Prevention of Restenosis ITalian Study (ESPRIT)

BACKGROUND AND OBJECTIVE

Previous trials of omega-3 fatty acids (omega-3 FA) for restenosis prevention after percutaneous transluminal coronary angioplasty (PTCA) have yielded conflicting results. We tested the hypothesis that long-term administration of omega-3 FA before PTCA may have significant effects on restenosis.

METHODS

We randomized 339 patients in a double-blind, placebo-controlled study of omega-3 FA (as an ethyl ester preparation given as 6 1-g capsules providing 3 g eicosapentaenoic acid and 2.1 g docosahexaenoic acid/d started 1 month before PTCA and given for 1 month thereafter, then continued at half-dose for 6 months) versus an olive oil placebo. Of these, 257 patients (125 on omega-3 FA, 132 on placebo) well matched for risk factors underwent successful balloon-only PTCA (280 total lesions) and were evaluable at 6 months with repeat angiography. Restenosis was defined at quantitative angiography as a recurrence of >50% diameter stenosis in the dilated vessel (Definition I) and as >50% loss of the short-term gain immediately after PTCA (Definition II).

RESULTS

Restenosis rates per vessel were 29.4% and 31.6% in the omega-3 FA group, and 39.6% and 35.4% in the placebo group according to Definitions I (P =.04) and II (P = not significant), respectively. Restenosis rates per patient were 31.2% and 33.6% in the omega-3 FA group, and 40.9% and 37.1% in the placebo group according to Definitions I (P =.05) and II (P = not significant), respectively.

CONCLUSIONS

With a long treatment before PTCA, omega-3 FA produced a small but significant decrease in the restenosis rate compared with placebo.

Tissue-specific expression of human lipoprotein lipase in the vascular system affects vascular reactivity in transgenic mice

1. The role of smooth muscle-derived lipoprotein lipase (LPL) that translocates to the endothelium surface on vascular dysfunction during atherogenesis is unclear. Thus, the role of vascular LPL on blood vessel reactivity was assessed in transgenic mice that specifically express human LPL in the circulatory system. 2. Aortic free fatty acids (FFAs) were increased by 69% in the transgenic mice expressing human LPL in aortic smooth muscle cells (L2LPL) compared with their non-transgenic littermates (L2). 3. Contractility to KCl was increased by 33% in aortae of L2LPL mice. Maximal contraction to phenylephrine (PE) was comparable in L2 and L2LPL animals, while the frequency of tonus oscillation to PE increased by 104% in L2LPL mice. 4. In L2LPL animals, *NO mediated relaxation to acetylcholine (ACh) and ATP was reduced by 47 and 32%, respectively. In contrast, endothelium-independent relaxation to sodium nitroprusside (SNP) was not different in both groups tested. 5. ATP-initiated Ca(2+) elevation that triggers *NO formation was increased by 41% in single aortic endothelial cells freshly isolated from L2LPL animals. 6. In aortae from L2LPL mice an increased *O(2)(-) release occurred that was normalized by removing the endothelium and by the NAD(P)H oxidase inhibitor DPI and the PKC inhibitor GF109203X. 7. The reduced ACh-induced relaxation in L2LPL animals was normalized in the presence of SOD, indicating that the reduced relaxation is due, at least in part, to enhanced *NO scavenging by *O(2)(-). 8. These data suggest that despite normal lipoprotein levels increased LPL-mediated FFAs loading initiates vascular dysfunction via PKC-mediated activation of endothelial NAD(P)H oxidase. Thus, vascular LPL activity might represent a primary risk factor for atherosclerosis independently from cholesterol/LDL levels.

Unsaturated fatty acids selectively induce an inflammatory environment in human endothelial cells

BACKGROUND

Activation of the vascular endothelium by dietary fatty acids may be among the most critical early events in the development of atherosclerosis. However, the specific effects of fatty acids on inflammatory responses in endothelial cells are not fully understood.

OBJECTIVE

The present study focused on the induction of inflammatory genes in human endothelial cells exposed to individual dietary fatty acids. Because of the significance of nuclear factor kappaB (NF-kappaB) and activator protein 1 (AP-1) in the regulation of inflammatory gene expression, we also determined the effects of fatty acids on NF-kappaB and AP-1 transcriptional activation.

DESIGN

Human umbilical vein endothelial cells were exposed to dietary mono- and polyunsaturated 18-carbon fatty acids. Transcriptional activation of NF-kappaB and AP-1 was determined in human umbilical vein endothelial cells transfected with reporter constructs regulated by these transcription factors. Induction of the inflammatory genes was studied by use of reverse transcriptase-polymerase chain reaction.

RESULTS

Of the fatty acids studied, linoleic acid stimulated NF-kappaB and AP-1 transcriptional activation the most. In addition, treatment with this fatty acid markedly enhanced messenger RNA levels of tumor necrosis factor alpha, monocyte chemoattractant protein 1, vascular cell adhesion molecule 1, and intercellular adhesion molecule 1. Treatment with linolenic acid stimulated only a moderate induction of the genes encoding for these inflammatory mediators, and exposure to oleic acid either had no effect or resulted in decreased inflammatory gene messenger RNA. In addition, exposure to both linoleic and linolenic acids strongly stimulated induction of the phospholipid hydroperoxide glutathione peroxidase gene.

CONCLUSION

Specific unsaturated dietary fatty acids, particularly linoleic acid, can selectively stimulate the development of a proinflammatory environment within the vascular endothelium.

Interaction between the Gln-Arg 192 variants of the paraoxonase gene and oleic acid intake as a determinant of high-density lipoprotein cholesterol and paraoxonase activity

Olive oil, rich in oleic acid, could play a particular beneficial role in the anti-atherogenic effects attributed to the Mediterranean diet. Paraoxonase (PON1) has emerged as the component of high-density lipoproteins (HDL) most likely to explain its ability to attenuate the oxidation of low-density lipoproteins. We hypothesised that oleic acid intake might be associated with changes in PON1-HDL associated particles, and investigated the impact, if any, on this association of the PON1-192 polymorphism, a common polymorphism that strongly modulates PON1 activity. Six hundred and fifty-four men randomly selected from the census were studied. Oleic acid intake was calculated from a 72-h recall questionnaire with specific software. Oleic acid intake groups (low vs. high) were created by stratifying the population according the median value as a cut-point. After adjusting for confounding variables, high oleic acid intake was associated with increased HDL cholesterol levels and PON1 activity only in subjects with the QR and the RR genotypes, respectively. Analyses of the variance showed a statistically significant interaction between PON1-192 genotypes and oleic acid intake for log PON1 activity (P=0.005) and a marginally significant interaction for HDL cholesterol (P=0.066). These results suggest that the beneficial effect of increasing oleic acid intake on HDL and PON1 activity at population level is especially observed in subjects carrying the R allele of the PON1-192 polymorphism.

High-Energy Diets, Fatty Acids and Endothelial Cell Function: Implications for Atherosclerosis

Diets high in fat and/or calories can lead to hypertriglyceridemia and postprandial lipemia and thus are considered a risk factor for the development of atherosclerosis. Plasma chylomicron levels are elevated in humans after consuming a high-fat meal, and hepatic synthesis of VLDL is increased when caloric intake is in excess of body needs. High lipoprotein lipase activity and subsequent hydrolysis of triglyceride-rich lipoproteins may be an important source of elevated concentrations of fatty acid anions in the proximity to the endothelium and hence a major risk factor for atherosclerosis. We have shown that selected fatty acids, as well as lipoprotein lipase-derived remnants of lipoproteins isolated from hypertriglyceridemic subjects, can activate vascular endothelial cells and disrupt endothelial integrity. Our studies suggest that omega-6 fatty acids, and especially linoleic acid, cause endothelial cell dysfunction most markedly as well as can potentiate TNF-mediated endothelial cell injury. We propose that high-energy diets, and especially diets rich in linoleic acid, are atherogenic by contributing to an imbalance in cellular oxidative stress/antioxidant status of the endothelium, which can lead to activation of oxidative stress-responsive transcription factors, inflammatory cytokine production and the expression of adhesion molecules. Our data also suggest that nutrients, which have antioxidant and/or membrane stabilizing properties, can protect endothelial cells. These findings contribute to the understanding of the interactive role of high fat/calorie diets and subsequent hypertriglyceridemia with inflammatory components and nutrients that exhibit antiatherogenic properties in the development of atherosclerosis. Moreover, results from our research further support the concept that high-fat/calorie diets and associated postprandial hypertriglyceridemia are significant risk factors for atherosclerosis.

The postprandial effect of components of the Mediterranean diet on endothelial function

OBJECTIVES

This study investigated the postprandial effect of components of the Mediterranean diet on endothelial function, which may be an atherogenic factor.

BACKGROUND

The Mediterranean diet, containing olive oil, pasta, fruits, vegetables, fish, and wine, is associated with an unexpectedly low rate of cardiovascular events. The Lyon Diet Heart Study found that a Mediterranean diet, which substituted omega-3-fatty-acid-enriched canola oil for the traditionally consumed omega-9 fatty-acid-rich olive oil, reduced cardiovascular events.

METHODS

We fed 10 healthy, normolipidemic subjects five meals containing 900 kcal and 50 g fat. Three meals contained different fat sources: olive oil, canola oil, and salmon. Two olive oil meals also contained antioxidant vitamins (C and E) or foods (balsamic vinegar and salad). We measured serum lipoproteins and glucose and brachial artery flow-mediated vasodilation (FMD), an index of endothelial function, before and 3 h after each meal.

RESULTS

All five meals significantly raised serum triglycerides, but did not change other lipoproteins or glucose 3 h postprandially. The olive oil meal reduced FMD 31% (14.3 +/- 4.2% to 9.9 +/- 4.5%, p = 0.008). An inverse correlation was observed between postprandial changes in serum triglycerides and FMD (r = -0.47, p < 0.05). The remaining four meals did not significantly reduce FMD.

CONCLUSIONS

In terms of their postprandial effect on endothelial function, the beneficial components of the Mediterranean and Lyon Diet Heart Study diets appear to be antioxidant-rich foods, including vegetables, fruits, and their derivatives such as vinegar, and omega-3-rich fish and canola oils.

Fatty acid modulation of endothelial activation

Dietary balance of long-chain fatty acids may influence processes involving leukocyte-endothelial interactions, such as atherogenesis and inflammation, that involve increased endothelial expression of leukocyte adhesion molecules, or endothelial activation. We compared the ability of various saturated, monounsaturated, and polyunsaturated fatty acids to modulate endothelial activation. Consumption of the n-3 fatty acid docosahexaenoic acid (DHA; 22:6n-3) reduced endothelial expression of vascular cell adhesion molecule 1 (VCAM-1), E-selectin, intercellular adhesion molecule 1 (ICAM-1), interleukin 6 (IL-6), and IL-8 in response to IL-1, IL-4, tumor necrosis factor, or bacterial endotoxin, with a half-maximal inhibitory concentration (IC(50)) of 1-25 micromol, ie, in the range of nutritionally achievable plasma concentrations. The magnitude of this effect paralleled its incorporation into cellular phospholipids. DHA also reduced the adhesion of human monocytes and monocytic U937 cells to cytokine-stimulated endothelial cells. These effects were accompanied by a reduction in VCAM-1 messenger RNA, indicating a pretranslational effect. To assess structural fatty acid determinants of VCAM-1 inhibitory activity, we compared various saturated, monounsaturated, and n-6 and n-3 polyunsaturated fatty acids for their VCAM-1 inhibitory activity. Saturated fatty acids did not inhibit cytokine-induced expression of adhesion molecules. However, a progressive increase in inhibitory activity was observed with dietary intake of fatty acids with the same chain length but increasing double bonds, ie, from monounsaturated to n-6 and, further, to n-3 fatty acids. Thus, the greater number of double bonds seems critical for the greater activity of n-3 compared with n-6 fatty acids in inhibiting endothelial activation. These properties are likely to be relevant to the antiatherogenic and antiinflammatory properties of n-3 fatty acids.

Effects of diet and of dietary components on endothelial leukocyte adhesion molecules

Endothelial-leukocyte adhesion molecules are involved in processes regulating the selective attachment of leukocytes to the vessel wall, which participate in tissue inflammation, atherogenesis, and immunity. There has been recent appreciation that diet or specific dietary components may modulate such processes. Highly unsaturated-- particularly omega-3 -- fatty acids and antioxidants are receiving increasing attention in this regard as potential antiatherogenic and anti-inflammatory agents. The vascular surface expression of endothelial leukocyte molecules can also be reflected by plasma levels of "soluble" adhesion molecules, thus allowing the assessment of the effects of diet and selected dietary components on these processes in vivo.

The inhibition of endothelial activation by unsaturated fatty acids

Dietary long-chain fatty acids (FA) may influence pathological processes involving endothelial activation and leukocyte-endothelial interactions, such as inflammation and atherosclerosis. We previously showed that the n-3 FA docosahexaenoate (22:6n-3, DHA) inhibits cytokine-stimulated expression of endothelial-leukocyte adhesion molecules and soluble cytokines in the range of nutritionally achievable plasma concentrations. More recently we assessed structural determinants of VCAM-1 inhibition by FA. Cultured endothelial cells were incubated first with various saturated, monounsaturated, n-6 or n-3 polyunsaturated FA alone and then together with interleukin-1 or tumor necrosis factor. Saturated FA did not inhibit cytokine-induced endothelial activation, while a progressive increase in inhibitory activity was observed, for the same chain length, with the increase in double bonds accompanying the transition from monounsaturates to n-6 and, further, to n-3 FA. Comparison of various FA indicated no role of the double-bond position or configuration; the greater number of double bonds could explain the greater inhibitory activity of n-3 vs. n-6 FA. In order to ascertain mechanisms for these effects, we demonstrated inhibition of nuclear factor-kappaB (NF-kappaB) activation by DHA in parallel with a reduction in hydrogen peroxide (a critical mediator of NF-kappaB activation) released by endothelial cells either extracellularly or intracellularly. This suggests that a property related to fatty acid peroxidability (the presence of multiple double bonds) is related to inhibitory properties of hydrogen peroxide release and, consequently, of endothelial activation.