Oleic acid inhibits endothelial nitric oxide synthase by a protein kinase C-independent mechanism

Abnormal aortic fatty acid composition and small artery function in offspring of rats fed a high fat diet in pregnancy

1. Disturbances of the in utero environment are associated with an increased risk of cardiovascular disease in adulthood. In this study we have determined whether abnormal vascular function in the adult offspring of rats fed a high saturated fat diet in pregnancy is associated with altered plasma lipids or vascular fatty acid content. 2. Female Sprague-Dawley rats were fed a breeding diet (4 % fat) or a diet high in saturated fat (20 % fat) for 10 days prior to and throughout pregnancy, and during weaning. Female offspring were then fed a maintenance diet (3 % fat) until 160 days of age. 3. Endothelium-dependent relaxation induced by acetylcholine was blunted in isolated branches of the femoral artery from 160-day-old female offspring of dams fed the saturated fat diet when compared with female offspring of dams fed the breeding diet. These offspring exhibited elevated plasma triglyceride and reduced plasma high density lipoprotein cholesterol concentrations. 4. The fatty acid composition of the aortas was abnormal, with a marked reduction in the content of arachidonic and docosahexaenoic acids. 5. This study demonstrates that a high fat diet in pregnant rats produces abnormal vascular function, plasma lipid disturbances and altered vascular fatty acid content in their female offspring during adulthood.

Endothelium-dependent vasodilation is related to the fatty acid composition of serum lipids in healthy subjects

The fatty acid (FA) composition of the serum lipids has been associated with cardiovascular disease (CVD). As an attenuated endothelium-dependent vasodilation (EDV) has been suggested as an early marker of atherosclerosis, we investigated the relationships between the proportion of FA in serum lipids (cholesterol esters and phospholipids) together with the levels of serum LDL- and HDL-cholesterol and triglycerides and EDV, as well as endothelium-independent vasodilation (EIDV). Fifty-six healthy subjects (31 men and 25 women), aged between 20 and 69 years, underwent measurements of forearm blood flow (FBF) at rest and during local infusion of 2 and 4 microg/min of metacholine (Mch, evaluating EDV), 5 and 10 microg/min of sodium nitroprusside (SNP, evaluating endothelium-independent vasodilation, EIDV) using venous occlusion plethysmography. An index of endothelial function was calculated as the ratio between EDV and EIDV. The proportion of palmitic (16:0) and palmitoleic (16:1) acids were inversely related (r=-0.35 and -0.35, P<0.01 for both), while linoleic acid (18:2 n6) and the HDL-cholesterol concentration were positively related (r=0.35 and 0.36, P<0.01 for both) to the endothelial function index. In multiple regression analysis also including age and gender, palmitoleic acid and HDL-cholesterol were significant independent predictors of endothelial function. Alfa-linolenic acid (18:3 n3) was positively correlated to both EDV and EIDV (r=0.40 and 0.43, P<0.01 for both), indicating a protective effect of this essential FA on vasodilation in general. It is concluded that the FA composition of serum lipids, partly reflecting the composition of dietary fat and previously associated with the development of CVD, was associated with endothelial function in apparently healthy subjects.

An ordinary mixed meal transiently impairs endothelium-dependent vasodilation in healthy subjects

This study was designed to evaluate the effects of an ordinary mixed meal on endothelium-dependent vasodilation. Ten young healthy volunteers were given a mixed meal (minced meat sauce with rice, 900 kcal, 34% of the energy content was fat). In the fasting state, at 60 and 120 min after the start of the meal, endothelium-dependent vasodilation and endothelium-independent vasodilation were evaluated by local infusion of metacholine (4 microg min (-1)) and sodium nitroprusside (10 microg min (-1)) in the brachial artery. Blood flow in the forearm was measured using venous occlusion plethysmography. Endothelium-dependent vasodilation decreased from 15.4 +/- 3.3 (mean +/- SD) at fasting to 13.7 +/- 3.5 mL min (-1) (100 mL tissue)-1 (P < 0.01) 60 min after feeding, but had returned to the fasting level at 120 min. At 60 min, but not in the fasting state, the serum level of free fatty acids was inversely related to endothelium-dependent vasodilation (r=-0.74, P < 0.05), although no significant net changes in FFA levels were seen. Endothelium-independent vasodilation was not affected by the mixed meal. No similar attenuations in endothelium-dependent vasodilation were seen during control meals. In conclusion, an ordinary mixed meal transiently attenuated endothelium-dependent vasodilation. Free fatty acids may be involved in this effect on endothelial function.

New developments in mechanisms of obesity-induced hypertension: role of adipose tissue

Hypertension develops in almost 60% of obese individuals. Apart from the recent observation of obesity-associated structural changes in kidney structure that may lead to enhanced tubular sodium reabsorbtion, reports of paracrine and hormonal factors derived from adipose tissue have prompted speculations about the role of adipose tissue in the pathophysiology of obesity-induced hypertension. We summarize recent data on leptin's sympathoexcitatory actions, the possible influence of adipose tissue on atrial natriuretic peptide levels, and the formation of vasoactive substances, such as angiotensin II and nonesterified fatty acids, by adipocytes. The mechanisms discussed herein may contribute to the typical findings in obesity-induced hypertension, including volume expansion, sodium retention, enhanced sympathetic nervous system activity, increased activity of the systemic renin-angiotensin system, low atrial natriuretic peptide levels, and disturbed glucose and insulin metabolism. Together, these data strengthen the hypothesis that adipose tissue is potentially a major regulator of cardiovascular-renal function.

Nonesterified fatty acids in blood pressure control and cardiovascular complications

The fact that cardiovascular risk factors cluster among individuals with the insulin resistance syndrome strongly suggests a common pathogenetic denominator. For many years, abnormalities of nonesterified fatty acid metabolism have been implicated in the disturbances of carbohydrate and lipid metabolism that characterize the cluster. However, until more recently, evidence implicating fatty acids in the hemodynamic and vascular abnormalities that affect patients with this syndrome was lacking. Observations from epidemiological, clinical, and basic science suggest that fatty acids can raise blood pressure and contribute to the development of hypertension. The effects of fatty acids on blood pressure may be mediated in part by inhibition of endothelial nitric oxide synthase activity and endothelium-dependent vasodilation. Fatty acids can also increase alpha1-adrenoceptor-mediated vascular reactivity and induce vascular smooth muscle migration and proliferation. The adverse effects of fatty acids appear to be mediated in part through induction of oxidative stress. Fatty acids interact with other components of the risk factor cluster, including increased angiotensin II, to synergistically augment oxidative stress in cultured vascular smooth muscle cells. Oxidative stress is implicated in the pathogenesis of insulin resistance, hypertension, vascular remodeling, and vascular complications. A clearer definition of the specific reactive oxygen signaling pathways involved and interventions aimed at altering these pathways could lead to more rationale antioxidant therapy and improved outcomes.

The role of methyl-linoleic acid epoxide and diol metabolites in the amplified toxicity of linoleic acid and polychlorinated biphenyls to vascular endothelial cells

Selected dietary lipids may increase the atherogenic effects of environmental chemicals, such as polychlorinated biphenyls (PCBs), by cross-amplifying mechanisms leading to dysfunction of the vascular endothelium. We have shown previously that the omega-6 parent fatty acid, linoleic acid, or 3,3',4,4'-tetrachlorobiphenyl (PCB 77), an aryl hydrocarbon (Ah) receptor agonist, independently can cause disruption of endothelial barrier function. Furthermore, cellular enrichment with linoleic acid can amplify PCB-induced endothelial cell dysfunction. We hypothesize that the amplified toxicity of linoleic acid and PCBs to endothelial cells could be mediated in part by cytotoxic epoxide metabolites of linoleic acid called leukotoxins (LTX) or their diol derivatives (LTXD). Exposure to LTXD resulted in a dose-dependent increase in albumin transfer across endothelial cell monolayers, whereas this disruption of endothelial barrier function was observed only at a high concentration of LTX. Pretreatment with the cytosolic epoxide hydrolase inhibitor 1-cyclohexyl-3-dodecyl urea partially protected against the observed LTX-induced endothelial dysfunction. Endothelial cell activation mediated by LTX and/or LTXD also enhanced nuclear translocation of the transcription factor NF-kappa B and gene expression of the inflammatory cytokine IL-6. Inhibiting cytosolic epoxide hydrolase decreased the LTX-mediated induction of both NF-kappa B and the IL-6 gene, whereas the antioxidant vitamin E did not block LTX-induced endothelial cell activation. Most importantly, inhibition of cytosolic epoxide hydrolase blocked both linoleic acid-induced cytotoxicity, as well as the additive toxicity of linoleic acid plus PCB 77 to endothelial cells. Interestingly, cellular uptake and accumulation of linoleic acid was markedly enhanced in the presence of PCB 77. These data suggest that cytotoxic epoxide metabolites of linoleic acid play a critical role in linoleic acid-induced endothelial cell dysfunction. Furthermore, the severe toxicity of PCBs in the presence of linoleic acid may be due in part to the generation of epoxide and diol metabolites. These findings have implications in understanding interactive mechanisms of how dietary fats can modulate dysfunction of the vascular endothelium mediated by certain environmental contaminants.

Cellular regulation of endothelial nitric oxide synthase

Renal function is highly dependent on endothelium-derived nitric oxide (NO). Several renal disorders have been linked to impaired NO bioavailability. The enzyme that is responsible for the synthesis of NO within the renal endothelium is endothelial NO synthase (eNOS). eNOS-mediated NO generation is a highly regulated cellular event, which is induced by calcium-mobilizing agonists and fluid shear stress. eNOS activity is regulated at the transcriptional level but also by a variety of modifications, such as acylation and phosphorylation, by its cellular localization, and by protein-protein interactions. The present review focuses on the complex regulation of eNOS within the endothelial cell.

Free fatty acids/triglycerides increase ocular and subcutaneous blood flow

Elevated plasma free fatty acids (FFA) induce skeletal muscle insulin resistance and impair endothelial function. The aim of this study was to characterize the acute hemodynamic effects of FFA in the eye and skin. A triglyceride (Intralipid 20%, 1.5 ml/min)/heparin (bolus: 200 IU; constant infusion rate: 0.2 IU. kg(-1). min(-1)) emulsion or placebo was administered to 10 healthy subjects. Measurements of pulsatile choroidal blood flow with laser interferometry, retinal blood flow with the blue field entoptic technique, peak systolic and end diastolic blood velocity (PSV, EDV) in the ophthalmic artery with Doppler sonography, and subcutaneous blood flow with laser Doppler flowmetry were performed during an euglycemic somatostatin-insulin clamp over 405 min. Plasma FFA/triglyceride elevation induced a rise in pulsatile choroidal blood flow by 25 +/- 3% (P < 0.001) and in retinal blood flow by 60 +/- 23% (P = 0.0125). PSV increased by 27 +/- 8% (P = 0.001), whereas EDV was not affected. Skin blood flow increased by 149 +/- 38% (P = 0.001). Mean blood pressure and pulse rate remained unchanged, whereas pulse pressure amplitude increased by 17 +/- 5% (P = 0.019). Infusion of heparin alone had no hemodynamic effect in the eye or skin. In conclusion, FFA/triglyceride elevation increases subcutaneous and ocular blood flow with a more pronounced effect in the retina than in the choroid, which may play a role for early changes of ocular perfusion in the insulin resistance syndrome.

Ascorbic acid improves postischemic vasodilatation impaired by infusion of soybean oil into canine iliac artery

This study was conducted to (a) assess postischemic vasodilatation by changes in the vascular cross-sectional area using simultaneous intravascular two-dimensional and Doppler ultrasound before and after the infusion of Intralipid (Pharmacia & Upjohn, Peapack, NJ, U.S.A.); (b) evaluate how antioxidant ascorbic acid modifies the effects of Intralipid on postischemic vasodilatation: and (c) clarify the changes in plasma nitrite and nitrate (NOx-) levels after the infusion of Intralipid with and without ascorbic acid. Twenty-eight mongrel dogs were used to measure for vascular cross-sectional area and average instantaneous peak velocity in the iliac arteries after the 5-min occlusion of the arteries. Postischemic vasodilatation was impaired after the infusion of Intralipid (20%, 2 ml/kg) and this impaired response was reversed by the co-administration of ascorbic acid (30 mg/kg). NG-monomethyl-L-arginine completely abolished postischemic vasodilatation. Plasma NOx levels were significantly reduced after the infusion of Intralipid compared with baseline (11.6+/-0.4 vs. 12.9+/-0.3 microM, p = 0.025) and after infusion of Intralipid with ascorbic acid compared with baseline (11.8+/-0.5 vs. 13.1+/-0.4 microM, p = 0.047). We concluded that ascorbic acid reverses the endothelial dysfunction induced by Intralipid without increasing plasma NOx- levels and that deactivation of nitric oxide by oxidative stress is a primary contributor to Intralipid-induced impaired vasodilation.

Dietary fat-induced increase in blood pressure and insulin resistance in rats

OBJECTIVES

To determine whether the dietary-fat-induced increase in blood pressure is caused by excess energy intake or the fat composition of the diet, what type of fat increases the blood pressure, and whether insulin resistance is involved in the dietary-fat-induced increase in blood pressure.

METHODS

In a series of experiments, rats received: chow alone or chow supplemented with lard or sucrose to provide 33% of a total energy content increased by 50%; chow alone or chow in which 50% of the energy content was from substituted lard, safflower oil or medium-chain triglyceride oil; or chow alone or chow in which 50% of the energy content was from substituted lard, with or without troglitazone. Systolic blood pressure (SBP) was measured every week during each 8-week feeding period. A steady-state serum glucose method was used to determine the insulin sensitivity after the lard substitution with or without troglitazone.

RESULTS

Both the lard and sucrose enrichment increased SBP and body weight compared with controls. Lard substitution significantly increased SBP and immunoreactive insulin, although body weight did not differ from control. Neither a diet substituted with safflower oil nor one substituted with medium-chain triglyceride oil influenced SBP. Troglitazone completely inhibited the increase in SBP and immunoreactive insulin induced by the lard. The steady-state serum glucose concentration was significantly greater after the lard substitution than after isoenergetic chow; this effect also was reversed by troglitazone.

CONCLUSION

Chronic feeding with lard increased SBP in rats, independently of excess energy intake. Of the fats tested, lard exerted an intrinsic pressor effect. Troglitazone reversed the lard-induced increase in SBP.

Inhibition of nitric oxide synthesis increases erythrocyte membrane fluidity and unsaturated fatty acid content

Changes in the lipid composition of the membrane affect its fluidity and function. These variables are altered in various forms of hypertension. Our hypothesis was that the rapid increase in blood pressure (BP) caused by inhibition of nitric oxide production would lead to alterations in membrane fluidity similar to those observed in genetic hypertension. We used Nomega-nitro L-arginine methyl ester (L-NAME) and vehicle-treated (3 weeks) Wistar-Kyoto rats to study the effects of nitric oxide synthase (NOS) inhibition on membrane fluidity and lipid composition. Erythrocyte membrane fluidity was measured by fluorescence anisotropy. Membrane lipids were separated using Sep-Pak and thin-layer chromatography. Fatty acid methyl esters were produced and analyzed by gas chromatography-mass spectrometry. Nomega-nitro L-arginine methyl ester treatment increased BP and erythrocyte membrane fluidity. The phospholipid and unsaturated fatty acid levels in the membranes from the L-NAME-treated rats were consistent with the increase in fluidity (ie, more unsaturated fatty acid, in particular, arachidonic and docosahexaenoic acid) and a reduction in membrane sphingomyelin content. Fatty acid analysis of individual lipid groups suggested the changes in membrane fatty acid composition may be asymmetric, with the majority of the changes occurring in the outer leaflet. Inhibition of NOS results in changes in membrane composition that may explain the concurrent changes in fluidity. The increased membrane fluidity observed here contrasts with the reduced fluidity observed in genetic hypertension or unchanged fluidity in secondary hypertension. The effects could be related to NOS inhibition or may be a direct effect of L-NAME.

Linoleic acid and oleic acid increase the endothelin-1 binding and action in cultured rat aortic smooth muscle cells

An increase in circulating non-esterified fatty acids (NEFA) has been observed in patients with poorly controlled diabetes mellitus. To investigate whether fatty acids will affect the endothelin-1 (ET-1) receptor and thus contribute to the acceleration of atherosclerosis in diabetic patients, cultured rat aortic smooth muscle cells (SMC) were maintained in media containing higher (similar to those in diabetic patients) concentrations of oleic acid (OA) or linoleic acid (LA). The ET-1 binding and ET-1-stimulated thymidine uptake were then examined. We found that cells treated with OA (500 micromol/L) or LA (250 micromol/L) showed a significant increase in ET-1 receptor amount as demonstrated by Scatchard analysis (Bmax: 7.40 +/- 1.04 v 2.71 +/- 0.54 fmol/mg and 5.00 +/- 1.00 v 3.32 +/- 0.70 fmol/mg, respectively). No change in binding affinity was found. Moreover, both the basal and ET-1-stimulated thymidine uptake were enhanced by treatment with either LA (basal, 11,367 +/- 4,117 cpm/mg; LA, 13,933 +/- 4,003 cpm/mg; ET-1 (10(-8)), 16,931 +/- 4,412 cpm/mg; LA +/- ET-1 (10(-8)), 28,855 +/- 5,217 cpm/mg) or OA (basal, 4,912 +/- 1,193 cpm/mg, OA, 8,027 +/- 1,318 cpm/mg; ET-1 (10(-8)) 9,947 +/- 2,520 cpm/mg; OA + ET-1 (10(-8)), 16,761 +/- 1,740 cpm/mg). This enhancement in thymidine uptake was associated with an increase in cell number. Because ET-1 and its receptor are involved in atherogenesis, our findings suggested that increase in circulating NEFA may contribute to the acceleration of atherosclerosis in diabetic patients. Further studies to confirm its role in the vascular wall are warranted.

Natural bioactive substances in milk and colostrum: effects on the arterial blood pressure system

High blood pressure is a significant public health problem worldwide which is associated with increased risk of cardiovascular disease, stroke, and renal disease. The development of this disease is influenced by genetic and environmental factors. The results of many studies have linked increased consumption of milk and milk products with lower blood pressure and reduced risk of hypertension. The intake of several minerals found in milk has been demonstrated to have an inverse relationship with blood pressure. Peptides formed during the digestion of milk proteins have also been demonstrated to have a blood pressure lowering effect. Other components in milk that have been examined for their effects on blood pressure have been less promising. More recent data indicate that a dietary pattern that is low in fat, with fruits, vegetables, and low fat dairy products can significantly reduce blood pressure and lower risk of developing high blood pressure.

Metabolic complications of obesity. Pathophysiologic considerations

Given a specific research interest in human fatty acid metabolism, this article focuses primarily on the evidence surrounding the hypothesis that dysregulation of the fuel release function of fat cells (lipolysis) is an important contributing factor to the health hazards of obesity.

Effects of age, gender and metabolic factors on endothelium-dependent vasodilation: a population-based study

OBJECTIVES

A progressive decline in endothelium-dependent vasodilation (EDV) in the human forearm with age has previously been reported. The aim of this study was to evaluate the interplay between age, gender and metabolic factors on EDV in healthy subjects in a population-based study.

SETTING

Tertiary university hospital.

SUBJECTS AND DESIGN

Thirty-six healthy men and 30 women, aged 20-69 years, underwent measurements of forearm blood flow (FBF) at rest and during local infusions of 2 and 4 microg min-1 of metacholine (evaluating EDV) and 5 and 10 microg min-1 of sodium nitroprusside (evaluating endothelium-independent vasodilation, EIDV) and during reactive hyperaemia by venous occlusion plethysmography.

RESULTS

Age was inversely related to EDV (r = - 0.41, P < 0.05 in men; r = - 0.61, P < 0.01 in women) and maximal FBF during reactive hyperaemia in both men and women. EIDV was significantly related to age in an inverse way in women only. EDV was more pronounced in females than in males before menopause (48 +/- 3 SD years, 635 +/- 186 vs. 502 +/- 269% in males, P < 0.05), but similar in women and men thereafter (374 +/- 141 vs. 370 +/- 185% in men). The slope of the regression line for the relationship between age and EDV was flatter in premenopausal than in postmenopausal women (- 2.3 vs. - 6.4), whilst this slope was similar in younger and older men (- 5.5 vs. - 5.3). In multiple regression analysis, fasting blood glucose levels and the waist/hip ratio remained the only significant predictors of EDV in men (P < 0.01 for both), whilst age was the only significant independent predictor of EDV in women (P < 0.01).

CONCLUSION

The interplay between age and metabolic factors as determinants of endothelial function is different in healthy men and women.

Vascular effects of non-esterified fatty acids: implications for the cardiovascular risk factor cluster

Insulin resistance emerges as a central component of the risk factor cluster and is a likely contributor to vascular disease independently of traditional risk factors such as hypertension and diabetes mellitus. However, the intermediary mechanisms by which atherosclerosis is accelerated among patients with the insulin resistance syndrome remain inadequately defined. Most of the attention has centered on hyperinsulinemia and defects of insulin-mediated glucose disposal. However, we observed that obese hypertensive patients have elevated plasma concentrations of non-esterified fatty acids (NEFAs), including oleic acid, which are highly resistant to suppression by insulin. Resistance to insulin's fatty acid lowering action correlate with blood pressure in obese subjects independently of defects in glucose disposal. This observation raises the possibility that NEFAs have biologically significant effects on the cardiovascular system. In fact, oleic acid impairs nitric oxide synthase activity and endothelium-dependent vasorelaxation in vitro. Moreover, raising NEFAs in normal human volunteers to levels observed in obese hypertensive patients impairs lower extremity endothelium-dependent vasodilation and augments local and systemic vascular alpha1-adrenoceptor reactivity in normal volunteers. Thus, raising NEFAs replicates in healthy subjects important functional vascular changes implicated in the hypertension and atherosclerosis observed in patients with the risk factor cluster. At a molecular level, experiments in cultured vascular smooth muscle cells demonstrate that oleic acid activates a mitogenic signaling cascade which includes protein kinase C, reactive oxygen species and extracellular signal-regulated kinases. Each of these signaling events has been implicated in the structural and functional vascular changes which accompany the risk factor cluster. Collectively, these observations raise the possibility that fatty acids contribute to functional and structural vascular changes among insulin-resistant individuals. A better understanding of the signaling mechanisms by which NEFAs exert their vascular effects may facilitate novel and more effective therapeutic approaches to managing the cardiovascular risk factor cluster.

Effect of hyperinsulinaemia on renal function and nitrate/nitrite excretion in healthy subjects

1. In addition to its metabolic actions, insulin acts as a vasodilator in certain vascular beds, such as skeletal muscle. It has been shown that this effect is mediated by endothelium-derived nitric oxide (NO). Unlike in the skeletal muscle, insulin-NO interactions in the kidney, another major site of insulin action, have been less studied. The aim of the present study was to explore the role of NO in renal effects of hyperinsulinaemia in healthy subjects. 2. Changes in renal function and urinary nitrate/nitrite (NO2-/NO3-; Griess method) levels as a marker of renal production of NO were assessed during euglycaemic hyperinsulinaemic clamp and compared with normoinsulinaemic isovolaemic conditions (administration of the same amount of insulin/glucose-free vehicle) in 10 healthy male volunteers. 3. Hyperinsulinaemia was associated with a decrease in renal excretion of stable metabolites of NO (mean (+/- SEM) 0.56 +/- 0.12 vs 0.38 +/- 0.05 mumol/min, respectively; P < 0.05). In contrast, administration of the same volume of insulin-free vehicle resulted in elevation of urinary NO2-/NO3- (P < 0.05). The changes in renal sodium handling followed a similar pattern as changes in the renal excretion of NO2-/NO3- with a significantly different response to hyperinsulinaemia when compared with normoinsulinaemia (F = 12.2; P < 0.001). The mean arterial pressure, blood levels of low-density lipoprotein-cholesterol and free fatty acids, possible factors influencing renal and systemic NO production, remained constant throughout both experiments. 4. These results suggest that hyperinsulinaemia is associated, in healthy males, with a decrease in renal generation of NO. In contrast, mild volume expansion with insulin-free vehicle resulted in increased excretion of NO metabolites. This insulin-induced attenuation of renal NO synthesis may contribute to the anti-natriuretic actions of insulin.

Serum from preeclamptic women induces vascular cell adhesion molecule-1 expression on human endothelial cells in vitro: a possible role of increased circulating levels of free fatty acids

OBJECTIVE

The object was to determine whether serum from preeclamptic women induces expression of vascular cell adhesion molecule-1 on cultured endothelial cells.

STUDY DESIGN

Endothelial cells were incubated with medium containing 20% serum (volume/volume) either from women with preeclampsia (n = 15) or from women with normal pregnancies (n = 15) matched for maternal age, gestational age, and parity. A further matched set of samples (n = 10) was exposed to endothelial cells that had previously been incubated in the presence or absence of vitamin E (40 micromol/L final concentration). Free fatty acids were determined in each sample. A mixture of free fatty acids (linoleic, oleic, and palmitic acids, 1:1:1) was added to serum from control subjects in increasing concentrations (70-280 micromol/L final concentration) to emulate preeclamptic serum and the preparation was exposed to endothelial cells. In each experiment vascular cell adhesion molecule-1 expression was determined after 16 hours of exposure by an enzyme-linked immunosorbent assay technique performed on the cell monolayer.

RESULTS

Preeclamptic serum had higher levels of free fatty acids than did that of control subjects (0.71 mmol/L, 95% confidence level 0.5-0.93, vs 0.36 mmol/L, 95% confidence level 0.28-0.43). There was a statistically significant increase in vascular cell adhesion molecule-1 expression on the endothelial cells exposed to preeclamptic serum compared with those exposed to control serum (optical density 0.17 vs 0.11). Vitamin E reduced the vascular cell adhesion molecule-1 expression of endothelial cells exposed both to preeclamptic and to control serum samples in a nonspecific manner. Addition of free fatty acids to normal pregnancy serum to mimic the effect of preeclampsia resulted in increased expression of vascular cell adhesion molecule-1 on the cells.

CONCLUSION

Preeclamptic serum induces vascular cell adhesion molecule-1 expression on human endothelial cells in vitro, an effect also produced by fatty acids. The elevated level of free fatty acids in women with preeclampsia may contribute to increased vascular cell adhesion molecule expression in vivo.

The atherogenic lipoprotein phenotype and vascular endothelial dysfunction

There is accumulating evidence that elevated plasma triglycerides and related abnormalities constitute an independent cardiovascular risk factor. Although the pathogenetic basis for the apparent relationship between elevated triglyceride-rich lipoproteins and CAD is still uncertain, evidence is accumulating to suggest that endothelial dysfunction is involved. There is evidence to suggest that triglyceride-rich particles may be directly damaging to the endothelium; this may be principally via oxidative mechanisms. Triglyceride-rich particles can cross the endothelial barrier and enter the arterial wall, thus placing them in a position to promote direct endothelial damage. These particles stimulate endothelial expression of adhesion molecules and the prothrombotic factor PAI-1. By reducing LDL size and HDL cholesterol concentrations, thereby further increasing the endothelial oxidative burden, triglyceride-rich particles may indirectly promote endothelial dysfunction. In addition, free fatty acids, which are the major substrates for endogenous synthesis of triglyceride-rich particles, are also potentially damaging to the endothelium. This occurs via oxidative stress, by facilitating transfer of LDL across the endothelium, and by enhancing toxicity of triglyceride-rich particles. Finally, there is recent strong evidence to suggest that increased postprandial circulating concentrations of triglyceride-rich particles and remnant particles may be deleterious to the endothelium.

Expression of peroxisome proliferator-activated receptor alpha (PPAR alpha) in primary cultures of human vascular endothelial cells

The peroxisome proliferator-activated receptor (PPAR) is a member of the steroid nuclear receptor superfamily. Three types of PPARs have been described in humans: PPAR alpha, PPAR beta, and PPAR gamma. Here we investigated the levels of PPAR alpha mRNA in primary cultures of human umbilical venous endothelial cells (HUVEC), human umbilical arterial endothelial cells (HUAEC), human coronary arterial endothelial cells (HCAEC), and human aortic endothelial cells (HAEC), using the reverse transcriptase-polymerase chain reaction (RT-PCR). The HUVEC, HAEC, and HCAEC, but not the HUAEC, showed relatively low expression of PPAR alpha in comparison with liver, which was used as a positive control. Moreover, the partial sequences of the PCR-amplified products from HUVEC, HAEC, and HCAEC were similar to that of the PPAR alpha from human liver. The expression of PPAR alpha in cultured HAEC, which were induced by dexamethasone, was inhibited by insulin. In addition, PPAR alpha expression was also increased by benzafibrate or eicosapentaenoic acid with the physiological concentration. These results suggest that the PPAR alpha in endothelial cells may have the same physiological role as the expression of PPAR alpha in the liver.

Response of insulin, glucagon, lactate, and nonesterified fatty acids to glucose in visceral obesity with and without NIDDM: relationship to hypertension

Insulin, glucagon, glucose, nonesterified fatty acids (NEFA), and lactate response to oral glucose tolerance test (OGTT, 75 g glucose) and their correlation with mean blood pressure (BP), were studied in 10 normal subjects (N), 25 subjects with abdominal obesity (O), and 9 subjects with abdominal obesity and IGT or non-insulin-dependent diabetes (OD). O and OD patients, as compared to N subjects, showed increased fasting NEFA, lactate, insulin, and glucagon. NEFA area and insulin total and incremental areas were increased in O and OD (P < 0.001 in all instances). Glucagon total areas were increased only in OD (P < 0.01). Lactate total areas were increased in O (P < 0.001) and in OD (P < 0.01), while lactate incremental area was diminished in O and, even more, in OD subjects (P < 0.001 in both instances) and was inversely correlated with the basal level (P < 0.001). In all subjects as a whole, increase in NEFA area was weakly correlated with total and incremental insulinemic areas (P < 0.05) and more strongly correlated with glucagon and lactate areas (P < 0.01). Conversely, the incremental areas of lactate were negatively correlated with total insulin (P < 0.05), NEFA (P < 0.05), and glucagon (P < 0.001) areas. BP was increased in O (103.62 +/- 2.37) and, even more, in OD (109.41 +/- 5.22) compared to that seen in N (92.55 +/- 0.94 mm Hg), with P < 0.01, and was correlated with fasting insulin (P < 0.01) and glucose (P < 0.05) and, even more, with total (P < 0.001) and incremental (P < 0.01) insulin areas and NEFA areas (P < 0.001). Conversely, BP also was negatively correlated with incremental lactate area (P < 0.01) (similarly to insulin and NEFA area). Our data would suggest that in O and OD patients, insulin resistance is associated with elevated NEFA, insulin and glucagon as well as with high BP. since NEFA are inhibitors of Na,K-ATPase, they could contribute to elevate BP through the repression of this enzyme (which we have shown previously to be reduced in adipose tissue of obese subjects and correlated negatively with BP.

Fructose perfusion in rat mesenteric arteries impairs endothelium-dependent vasodilation

We demonstrated that the fructose-induced hypertensive rat, representative of the principal metabolic abnormalities found in a majority of hypertensive patients, i.e. hypertriglyceridemia, hyperinsulinemia and insulin resistance (Syndrome X), is associated with an impaired response to endothelium-dependent vasodilators and that fructose may directly contribute to this impairment. Twelve male Wistar rats were divided into two groups, one given 10% fructose (n=6); the other no fructose (n=6) for 40 days in the drinking water. Systolic blood pressure was measured via the tail cuff method. Perfusion pressure responses to acetylcholine, were measured in the isolated perfused mesenteric vascular bed. Constrictor or dilator responses were measured as increases or decreases, respectively, of the perfusion pressure at a constant flow (4 ml/min). Fructose-fed rats had significantly higher blood pressure, insulin and triglyceride levels than control animals. In phenylephrine constricted beds, the endothelium-dependent dilatation to acetylcholine (0.001 to 1 micromol) was attenuated in the fructose-fed group compared to control animals. Whether this abnormality results from the syndromes (hyperinsulinemia, hypertension and hypertriglyceridemia) associated with the fructose-fed animal model is unknown. We therefore hypothesized that fructose can impair the endothelium-dependent vasodilator response. This was evaluated by perfusing mesenteric arteries from normal rats with control mannitol (40 mM) or fructose (40 mM). Endothelium-dependent dilation to acetylcholine was impaired in fructose-perfused mesenteric arteries. Indomethacin restored the vasodilator response to acetylcholine, suggesting that a cyclooxygenase derivative mediates the impaired response. Thus, we conclude that fructose can contribute to the impaired endothelium-dependent response in the fructose-induced hypertensive rat model.

Elevated circulating free fatty acid levels impair endothelium-dependent vasodilation

We have recently shown that insulin-resistant obese subjects exhibit impaired endothelial function. Here, we test the hypothesis that elevation of circulating FFA to levels seen in insulin-resistant subjects can impair endothelial function. We studied leg blood flow responses to graded intrafemoral artery infusions of the endothelium-dependent vasodilator methacholine chloride (Mch) or the endothelium-independent vasodilator sodium nitroprusside during the infusion of saline and after raising systemic circulating FFA levels exogenously via a low- or high-dose infusion of Intralipid plus heparin or endogenously by an infusion of somatostatin (SRIF) to produce insulinopenia in groups of lean healthy humans. After 2 h of infusion of Intralipid plus heparin, FFA levels increased from 562+/-95 to 1,303+/-188 micromol, and from 350+/-35 to 3,850+/-371 micromol (P < 0.001) vs. saline for both low- and high-dose groups, respectively. Mch-induced vasodilation relative to baseline was reduced by approximately 20% in response to the raised FFA levels in both groups (P < 0.05, saline vs. FFA, ANOVA). In contrast, similar FFA elevation did not change leg blood flow responses to sodium nitroprusside. During the 2-h SRIF infusion, insulin levels fell, and FFA levels rose from 474+/-22 to 1,042+/-116 micromol (P < 0.01); Mch-induced vasodilation was reduced by approximately 20% (P < 0.02, saline vs. SRIF, ANOVA). Replacement of basal insulin levels during SRIF resulted in a fall of FFA levels from 545+/-47 to 228+/-61 micromol, and prevented the impairment of Mch-induced vasodilation seen with SRIF alone. In conclusion, (a) elevated circulating FFA levels cause endothelial dysfunction, and (b) impaired endothelial function in insulin-resistant humans may be secondary to the elevated FFA concentrations observed in these patients.

Nonesterified fatty acids in the pathogenesis of hypertension: theory and evidence

This paper approaches the hypothesis that fatty acids contribute to hypertension by examining possible interactions of nonesterified fatty acids with renal pressure-natriuresis, peripheral vascular resistance, and the central nervous barostat, three loci where long-term regulation of blood pressure is probably controlled. By inhibiting aldosterone secretion, nonesterified fatty acids may lower blood pressure by facilitating pressure-natriuresis. Oxygenated metabolites of fatty acids appear to stimulate aldosterone secretion. In different experimental situations, fatty acids either constrict or dilate arteries. There is no evidence of an effect of fatty acids on the central nervous barostat, but they do sensitize peripheral vessels to alpha-adrenergic stimuli. Obesity and diabetes are marked by increased incidence of hypertension, and elevated levels of fatty acids or their P450 oxygenated metabolites may contribute to this association. Drugs that influence plasma fatty acids, like heparin, do not have reproducible effects on blood pressure. Experimental evidence suggests but does not prove that nonesterified fatty acids can affect the long-term set-point of blood pressure.

Obesity/insulin resistance is associated with endothelial dysfunction. Implications for the syndrome of insulin resistance

To test the hypothesis that obesity/insulin resistance impairs both endothelium-dependent vasodilation and insulin-mediated augmentation of endothelium-dependent vasodilation, we studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of methacholine chloride (MCh) or sodium nitroprusside (SNP) during saline infusion and euglycemic hyperinsulinemia in lean insulin-sensitive controls (C), in obese insulin-resistant subjects (OB), and in subjects with non-insulin-dependent diabetes mellitus (NIDDM). MCh induced increments in LBF were approximately 40% and 55% lower in OB and NIDDM, respectively, as compared with C (P < 0.05). Euglycemic hyperinsulinemia augmented the LBF response to MCh by - 50% in C (P < 0.05 vs saline) but not in OB and NIDDM. SNP caused comparable increments in LBF in all groups. Regression analysis revealed a significant inverse correlation between the maximal LBF change in response to MCh and body fat content. Thus, obesity/insulin resistance is associated with (a) blunted endothelium-dependent, but normal endothelium-independent vasodilation and (b) failure of euglycemic hyperinsulinemia to augment endothelium-dependent vasodilation. Therefore, obese/insulin-resistant subjects are characterized by endothelial dysfunction and endothelial resistance to insulin's effect on enhancement of endothelium-dependent vasodilation. This endothelial dysfunction could contribute to the increased risk of atherosclerosis in obese insulin-resistant subjects.

Obesity/insulin resistance is associated with endothelial dysfunction. Implications for the syndrome of insulin resistance

To test the hypothesis that obesity/insulin resistance impairs both endothelium-dependent vasodilation and insulin-mediated augmentation of endothelium-dependent vasodilation, we studied leg blood flow (LBF) responses to graded intrafemoral artery infusions of methacholine chloride (MCh) or sodium nitroprusside (SNP) during saline infusion and euglycemic hyperinsulinemia in lean insulin-sensitive controls (C), in obese insulin-resistant subjects (OB), and in subjects with non-insulin-dependent diabetes mellitus (NIDDM). MCh induced increments in LBF were approximately 40% and 55% lower in OB and NIDDM, respectively, as compared with C (P < 0.05). Euglycemic hyperinsulinemia augmented the LBF response to MCh by - 50% in C (P < 0.05 vs saline) but not in OB and NIDDM. SNP caused comparable increments in LBF in all groups. Regression analysis revealed a significant inverse correlation between the maximal LBF change in response to MCh and body fat content. Thus, obesity/insulin resistance is associated with (a) blunted endothelium-dependent, but normal endothelium-independent vasodilation and (b) failure of euglycemic hyperinsulinemia to augment endothelium-dependent vasodilation. Therefore, obese/insulin-resistant subjects are characterized by endothelial dysfunction and endothelial resistance to insulin's effect on enhancement of endothelium-dependent vasodilation. This endothelial dysfunction could contribute to the increased risk of atherosclerosis in obese insulin-resistant subjects.