Oxidized low density lipoprotein displaces endothelial nitric-oxide synthase (eNOS) from plasmalemmal caveolae and impairs eNOS activation

Caveolae: a regulatory platform for nutritional modulation of inflammatory diseases

Dietary intervention strategies have proven to be an effective means of decreasing several risk factors associated with the development of atherosclerosis. Endothelial cell dysfunction influences vascular inflammation and is involved in promoting the earliest stages of lesion formation. Caveolae are lipid raft microdomains abundant within the plasma membrane of endothelial cells and are responsible for modulating receptor-mediated signal transduction, thus influencing endothelial activation. Caveolae have been implicated in the regulation of enzymes associated with several key signaling pathways capable of determining intracellular redox status. Diet and plasma-derived nutrients may modulate an inflammatory outcome by interacting with and altering caveolae-associated cellular signaling. For example, omega-3 fatty acids and several polyphenolics have been shown to improve endothelial cell function by decreasing the formation of ROS and increasing NO bioavailability, events associated with altered caveolae composition. Thus, nutritional modulation of caveolae-mediated signaling events may provide an opportunity to ameliorate inflammatory signaling pathways capable of promoting the formation of vascular diseases, including atherosclerosis.

Bicuspid aortic valve disease: the role of oxidative stress in Lrp5 bone formation

The bicuspid aortic valve is a common congenital cardiac anomaly, having a prevalence of 0.9% to 1.37% in the general population and a male preponderance ratio of 2:1. The recognition of a bicuspid aortic valve is clinically relevant because of its association with aortic stenosis or regurgitation, aortic aneurysm or dissection, and infective endocarditis. Although some patients with a bicuspid aortic valve may go undetected without clinical complications for a lifetime, the vast majority will require intervention, most often surgery, at some point. In fact, the natural history of bicuspid aortic valve is that of valve calcification and progressive stenosis that typically occur at a faster rate than in tricuspid aortic valves. This pattern of presentation supports the hypothesis that shear stress in patients with congenitally abnormal aortic valves may contribute to an earlier leaflet calcification. However, there is emerging research data showing that the valve calcification process might have a similar pathophysiologic process to that of vascular atherosclerosis. This review focuses on the current knowledge of the cellular mechanisms of bicuspid aortic valve.

Impact of oxLDL on Cholesterol-Rich Membrane Rafts

Numerous studies have demonstrated that cholesterol-rich membrane rafts play critical roles in multiple cellular functions. However, the impact of the lipoproteins on the structure, integrity and cholesterol composition of these domains is not well understood. This paper focuses on oxidized low-density lipoproteins (oxLDLs) that are strongly implicated in the development of the cardiovascular disease and whose impact on membrane cholesterol and on membrane rafts has been highly controversial. More specifically, we discuss three major criteria for the impact of oxLDL on membrane rafts: distribution of different membrane raft markers, changes in membrane cholesterol composition, and changes in lipid packing of different membrane domains. We also propose a model to reconcile the controversy regarding the relationship between oxLDL, membrane cholesterol, and the integrity of cholesterol-rich membrane domains.

The relationship of oxidative stress and cholesterol with dipping status before and after aerobic exercise training

OBJECTIVE

The purpose of this study was to examine the effects of aerobic exercise training (AEXT) on dipping status in pre-hypertensive and stage-1 hypertensive individuals. A secondary purpose was to evaluate whether AEXT alters oxidative stress and endothelial biomarkers correlated to dipping status.

METHODS

Twenty-three subjects underwent 24-h ambulatory blood pressure monitoring at baseline and after 6 months of AEXT. AEXT consisted of training at 70% VO(2max) 3 days/week for 6 months. Total cholesterol, high-density lipoprotein-cholesterol, low-density lipoprotein (LDL)-cholesterol, oxidized LDL (ox-LDL), triglycerides, urinary and plasma nitric oxide end-products, superoxide dismutase and 8-iso-PGF(2alpha) were measured before and after AEXT. Statistically, ANOVA and linear regression were used.

RESULTS

Before and after AEXT, there were no significant differences between dippers and non-dippers in any of the biomarkers except for total cholesterol following AEXT. In a sub-analysis following AEXT, 14 subjects retained their original dipping status, five subjects changed from dippers to non-dippers and four subjects changed from non-dippers to dippers. Significant differences existed between these groups in changes in total and LDL-cholesterol, ox-LDL, 8-iso-PGF(2alpha) and % Dip.

CONCLUSIONS

Changes in cholesterol levels but not oxidative stress or endothelial biomarkers were related to changes in BP variables following AEXT in dippers and non-dippers.

Oxidative stress-induced endothelial cell damage in thyroidectomized rat

Patients with hypothyroidism are considered to have an increased risk of developing atherosclerosis. Uncoupling of endothelial nitric oxide synthase from tetrahyrobiopterin, an essential cofactor, leads to the decrease of nitric oxide production and increase in reactive oxygen species. Both mechanisms contribute to atherosclerotic vascular disease. The aim of this study was to investigate whether hypothyroidism influences the systemic redox-state and the structure of aortic vascular endothelium in thyroidectomized rats. Twenty-eight Sprague-Dawley rats were randomly assigned to two groups; sham thyroidectomy and near-total thyroidectomy. Three weeks after surgery, nitric oxide in plasma, homocysteine, cysteine, glutathione levels and superoxide dismutase activity were measured in serum, and biopterine and creatinine were measured in urine. Aortic endothelium samples were processed for light and transmission electron microscopy. Although superoxide dismutase activity remained constant, urine biopterin levels and serum nitric oxide levels decreased in hypothyroid rats compared to their euthyroid controls. Aortic endothelium showed early features of atherosclerosis, and transmission electron microscopy revealed budding of caveolae in endothelial cells. It is concluded that hypothyroidism might lead to systemic oxidative stress with resultant endothelial dysfunction, and subsequent occurrence of atherosclerosis.

Upregulation of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) by 15-lipoxygenase-modified LDL in endothelial cells

OBJECTIVE

Lectin-like oxidized LDL receptor-1 (LOX-1), the endothelial receptor for OxLDL, is believed to be responsible for a number of OxLDL-induced effects in the endothelium.

METHODS AND RESULTS

In the present study we showed that LDL modified by 15-lipoxygenase (15LO-LDL), a form of minimally modified lipoprotein, beside its ability to induce pro-inflammatory responses such as oxidative stress and the expression of adhesion molecules, significantly increases LOX-1 expression in endothelial cells, both at transcriptional and at protein level. Such effect is likely to be mediated by p38 MAPK and NF-kB pathways. We then permanently overexpressed LOX-1 in an endothelial cell line and showed that 15LO-LDL were a ligand for LOX-1, and that the interaction LOX-1/15LO-LDL upregulated ICAM-1 surface expression.

CONCLUSION

Altogether these results indicate minimally modified LDL as a new inducer for LOX-1 expression and as a new ligand for LOX-1.

Diallyl disulfide and diallyl trisulfide protect endothelial nitric oxide synthase against damage by oxidized low-density lipoprotein

Garlic is viewed as an effective health food against atherosclerosis. In this study, we examined whether diallyl disulfide (DADS) and diallyl trisulfide (DATS) protect endothelial nitric oxide synthase (eNOS) activation against oxidized LDL (ox-LDL) insult and through what mechanism. We found that DADS and DATS reversed the suppression of eNOS Ser1177 phosphorylation by ox-LDL, and wortmannin abolished the reversal by DADS and DATS. Similarly, the inhibition of cellular cGMP and nitric oxide production by ox-LDL was reversed by DADS and DATS (p<0.05). This increase in nitric oxide bioavailability by the allyl sulfides was attenuated by wortmannin. Immunoprecipitation assay revealed that DADS and DATS preserved the interaction of eNOS with caveolin-1 in the membrane. In addition, DADS and DATS suppressed the reduction of the cellular eNOS protein content by ox-LDL. When cycloheximide was added to block protein synthesis, DADS and DATS suppressed eNOS protein degradation similarly to that noted by MG132. Ox-LDL increased chymotrypsin-like proteasome activity, and this increase was inhibited by the allyl sulfides and MG132 (p<0.05). These results suggest that DADS and DATS protect eNOS activity against ox-LDL insult. This protection can be attributed partly to their mediation of phosphatidylinositol 3-kinase/protein kinase B signaling and prevention of eNOS degradation.

Subcellular and cellular locations of nitric oxide synthase isoforms as determinants of health and disease

The effects of nitric oxide in biological systems depend on its steady-state concentration and where it is being produced. The organ where nitric oxide is produced is relevant, and within the organ, which types of cells are actually contributing to this production seem to play a major determinant of its effect. Subcellular compartmentalization of specific nitric oxide synthase enzymes has been shown to play a major role in health and disease. Pathophysiological conditions affect the cellular expression and localization of nitric oxide synthases, which in turn alter organ cross talk. In this study, we describe the compartmentalization of nitric oxide in organs, cells, and subcellular organelles and how its localization relates to several relevant clinical conditions. Understanding the complexity of the compartmentalization of nitric oxide production and the implications of this compartmentalization in terms of cellular targets and downstream effects will eventually contribute toward the development of better strategies for treating or preventing pathological events associated with the increase, inhibition, or mislocalization of nitric oxide production.

Interleukin-6 inhibits endothelial nitric oxide synthase activation and increases endothelial nitric oxide synthase binding to stabilized caveolin-1 in human vascular endothelial cells

OBJECTIVE

We hypothesized a possible mechanism for atherosclerosis in which interleukin-6 (IL-6) might affect the endothelial nitric oxide synthase (eNOS)-caveolin-1 interaction and result in decreased nitric oxide bioavailability in the setting of low-grade inflammation.

METHODS

Because eNOS and caveolin-1 are crucial for vascular tone control, we studied the effects of IL-6 on the expression and activation of eNOS and caveolin-1 in human vascular endothelial cells.

RESULTS

IL-6 inhibited the phosphorylation of eNOS at Ser1177 and the bradykinin-stimulated nitric oxide production; however, eNOS protein expression was not changed. In addition, IL-6 inhibited bradykinin-stimulated Akt phosphorylation at Ser473 and Thr 308 without affecting the Akt protein expression. IL-6 did not alter the mRNA level of caveolin-1; however, the caveolin-1 protein level was significantly increased dose-dependently. The binding of eNOS and caveolin-1 in endothelial cells, as demonstrated by coimmunoprecipitation assay, was increased by IL-6 treatment. IL-6 treatment was found to stabilize caveolin-1 protein and its half-life was estimated to prolong from 7.5 h to longer than 12 h. Furthermore, treatment with PD98059 and short interference RNA of extracellular signal-regulated kinase gene reversed the effects of IL-6 on eNOS and caveolin-1.

CONCLUSION

In addition to decreasing Akt phosphorylation, the results of this study demonstrate, for the first time, the molecular mechanism underlying the effect of IL-6 to decrease the nitric oxide bioavailability by increasing the half-life and, therefore, the protein levels of caveolin-1. The increased caveolin-1 proteins bind more eNOS and consequently decrease eNOS activation by reducing the Ser1177 phosphorylation.

TRPC1 is regulated by caveolin-1 and is involved in oxidized LDL-induced apoptosis of vascular smooth muscle cells

Oxidized low-density lipoprotein (oxLDL) induced-apoptosis of vascular cells may participate in plaque instability and rupture. We have previously shown that vascular smooth muscle cells (VSMC) stably expressing caveolin-1 were more susceptible to oxLDL-induced apoptosis than VSMC expressing lower level of caveolin-1, and this was correlated with enhanced Ca(2+) entry and pro-apoptotic events. In this study, we aimed to identify the molecular events involved in oxLDL-induced Ca(2+) influx and their regulation by the structural protein caveolin-1. In VSMC, transient receptor potential canonical-1 (TRPC1) silencing by ARN interference prevents the Ca(2+) influx and reduces the toxicity induced by oxLDL. Moreover, caveolin-1 silencing induces concomitant decrease of TRPC1 expression and reduces oxLDL-induced apoptosis of VSMC. OxLDL enhanced the cell surface expression of TRPC1, as shown by biotinylation of cell surface proteins, and induced TRPC1 translocation into caveolar compartment, as assessed by subcellular fractionation. OxLDL-induced TRPC1 translocation was dependent on actin cytoskeleton and associated with a dramatic rise of 7-ketocholesterol (a major oxysterol in oxLDL) into caveolar membranes, whereas the caveolar content of cholesterol was unchanged. Altogether, the reported results show that TRPC1 channels play a role in Ca(2+) influx and Ca(2+) homeostasis deregulation that mediate apoptosis induced by oxLDL. These data also shed new light on the role of caveolin-1 and caveolar compartment as important regulators of TRPC1 trafficking to the plasma membrane and apoptotic processes that play a major role in atherosclerosis.

A novel role for caveolin-1 in regulating endothelial nitric oxide synthase activation in response to H2O2 and shear stress

Previous studies have shown that acute increases in oxidative stress induced by the addition of hydrogen peroxide (H(2)O(2)) can increase endothelial nitric oxide synthase (eNOS) catalytic activity via an increase in the phosphorylation of eNOS at serine 1177. However, it is unclear how increased H(2)O(2) affects nitric oxide (NO) signaling when endothelial cells are exposed to biomechanical forces. Thus, the purpose of this study was to evaluate the acute effects of H(2)O(2) on NO signaling in the presence or absence of laminar shear stress. We found that acute sustained increases in cellular H(2)O(2) levels in bovine aortic endothelial cells did not alter basal NO generation but the NO produced in response to shear stress was significantly increased. This amplification in NO signaling was found to correlate with an H(2)O(2)-induced increase in eNOS localized to the plasma membrane and an increase in total caveolin-1 protein levels. We further demonstrated that overexpressing caveolin-1 increased eNOS localized to the plasma membrane again without altering total eNOS protein levels. We also found that caveolin-1 overexpression increased NO generation in response to shear stress but only in the presence of H(2)O(2). Conversely, depleting caveolin-1 with an siRNA decreased eNOS localized to the plasma membrane and abolished the enhanced NO generation. Finally, we found that expressing a caveolin-1 binding-site deletion mutant of eNOS in COS-7 cells decreased its plasma membrane localization and resulted in attenuated NO production in response to calcium activation. In conclusion, we have identified a new role for caveolin-1 in enhancing eNOS trafficking to the plasma membrane that seems to be involved in priming eNOS for flow-mediated activation under conditions of oxidative stress. To our knowledge, this is the first report that H(2)O(2) modulates eNOS activity by altering its subcellular location and that caveolin-1 can play a stimulatory role in NO signaling.

Oxidized LDL: diversity, patterns of recognition, and pathophysiology

Oxidative modification of LDL is known to elicit an array of pro-atherogenic responses, but it is generally underappreciated that oxidized LDL (OxLDL) exists in multiple forms, characterized by different degrees of oxidation and different mixtures of bioactive components. The variable effects of OxLDL reported in the literature can be attributed in large part to the heterogeneous nature of the preparations employed. In this review, we first describe the various subclasses and molecular composition of OxLDL, including the variety of minimally modified LDL preparations. We then describe multiple receptors that recognize various species of OxLDL and discuss the mechanisms responsible for the recognition by specific receptors. Furthermore, we discuss the contentious issues such as the nature of OxLDL in vivo and the physiological oxidizing agents, whether oxidation of LDL is a prerequisite for atherogenesis, whether OxLDL is the major source of lipids in foam cells, whether in some cases it actually induces cholesterol depletion, and finally the Janus-like nature of OxLDL in having both pro- and anti-inflammatory effects. Lastly, we extend our review to discuss the role of LDL oxidation in diseases other than atherosclerosis, including diabetes mellitus, and several autoimmune diseases, such as lupus erythematosus, anti-phospholipid syndrome, and rheumatoid arthritis.

oxLDL-induced decrease in lipid order of membrane domains is inversely correlated with endothelial stiffness and network formation

Oxidized low-density lipoprotein (oxLDL) is a major factor in development of atherosclerosis. Our earlier studies have shown that exposure of endothelial cells (EC) to oxLDL increases EC stiffness, facilitates the ability of the cells to generate force, and facilitates EC network formation in three-dimensional collagen gels. In this study, we show that oxLDL induces a decrease in lipid order of membrane domains and that this effect is inversely correlated with endothelial stiffness, contractility, and network formation. Local lipid packing of cell membrane domains was assessed by Laurdan two-photon imaging, endothelial stiffness was assessed by measuring cellular elastic modulus using atomic force microscopy, cell contractility was estimated by measuring the ability of the cells to contract collagen gels, and EC angiogenic potential was estimated by visualizing endothelial networks within the same gels. The impact of oxLDL on endothelial biomechanics and network formation is fully reversed by supplying the cells with a surplus of cholesterol. Furthermore, exposing the cells to 7-keto-cholesterol, a major oxysterol component of oxLDL, or to another cholesterol analog, androstenol, also results in disruption of lipid order of membrane domains and an increase in cell stiffness. On the basis of these observations, we suggest that disruption of lipid packing of cholesterol-rich membrane domains plays a key role in oxLDL-induced changes in endothelial biomechanics.

Anti-atherogenic effects of high-density lipoprotein on nitric oxide synthesis in the endothelium

1. The endothelium is critical in the control of vascular haemodynamics and haemostasis. Endothelial dysfunction, typically characterized by decreased nitric oxide bioavailability and response to endothelium-dependent agonists, is well accepted as a defining characteristic of early atherosclerosis. 2. Numerous epidemiological studies have reported that increased levels of circulating HDL are vasculoprotective and reduce the incidence of adverse cardiovascular events. Traditionally, these effects have been attributed to the ability of HDL to remove cholesterol from cells via reverse cholesterol transport. However, there is increasing evidence that the beneficial effects on the endothelium by HDL encompass its anti-inflammatory, antithrombotic and anti-oxidative properties, which include the release of nitric oxide (NO). 3. This review highlights recent findings on the importance of HDL in reducing atherosclerotic risk. We focus on the beneficial effects of HDL-induced NO release and how this relates to endothelial dysfunction and on the effect of HDL on vascular repair via endothelial progenitor cells.

A pharmacogenetics-based approach to reduce cardiovascular mortality with the prophylactic use of statins

Nitric oxide (NO) is the main endothelial-derived relaxation factor and plays a major role in cardiovascular homeostasis. This key signalling molecule is synthesised by a family of nitric oxide synthases (NOS), and the endothelial isoform (eNOS) is the most important for nitric oxide formation in the cardiovascular system. Cardiovascular drugs including statins increase eNOS expression and up-regulate NO formation, and this effect may be responsible for protective, pleiotropic effects produced by statins. However, the genetic background may also affect NO formation in the cardiovascular system, and recent studies have shown that genetic polymorphisms in the eNOS gene modify endogenous NO formation and the risk of developing cardiovascular diseases. For example, cases with the CC genotype for the T(-786)C polymorphism in the eNOS gene are at increased cardiovascular risk when compared with those with the TT genotype. Interestingly, pharmacogenetic studies have recently indicated that atorvastatin improves NO formation more clearly in these individuals. However, it is not known whether this polymorphism really increases cardiovascular morbidity and mortality, and whether atorvastatin or other statins attenuate the morbidity and mortality rates in cases with the CC genotype. If proved true, then statins-induced up-regulation of eNOS and increased NO formation could compensate for a genetic 'disadvantage' in cases with the CC genotype. This could be a significant advance in the prevention of cardiovascular events. It is necessary although to validate this hypothesis with clinical trials which will require a long follow-up to assess relevant clinical events and not only surrogate biomarkers.

Cholesterol depletion alters coronary artery myocyte Ca(2+) signalling in a stimulus-specific manner

Although there is evidence that caveolae and cholesterol play an important role in myocyte signalling processes, details of the mechanisms involved remain sparse. In this paper we have studied for the first time the clinically relevant intact coronary artery and measured in situ Ca(2+) signals in individual myocytes using confocal microscopy. We have examined the effect of the cholesterol-depleting agents, methyl-cyclodextrin (MCD) and cholesterol oxidase, on high K(+), caffeine and agonist-induced Ca(2+) signals. We find that cholesterol depletion produces a stimulus-specific alteration in Ca(2+) responses; with 5-HT (10microM) and endothelin-1 (10nM) responses being selectively decreased, the phenylephrine response (100microM) increased and the responses to high K(+) (60mM) and caffeine (10mM) unaffected. Agonist-induced Ca(2+) signals were restored when cholesterol was replenished using cholesterol-saturated MCD. In additional experiments, enzymatically isolated myocytes were patch clamped. We found that cholesterol depletion caused a selective modification of ion channel function, with whole cell inward Ca(2+) current being unaltered, whereas outward K(+) current was increased, due to BK(Ca) channel activation. There was also a significant decrease in cell capacitance. These data are discussed in terms of the involvement of caveolae in receptor localisation, Ca(2+) entry pathways and SR Ca(2+) release, and the role of these in agonist signalling.

Is exercise training an effective therapy targeting endothelial dysfunction and vascular wall inflammation?

There is an increasing evidence that endothelial dysfunction and vascular wall inflammation are present in all stages of atherosclerosis. Atherosclerosis does not have to necessarily progress to an acute clinical event. Several therapeutic strategies exist, such as exercise training, which mitigates endothelial dysfunction and inflammation. Exercise training consistently improves the nitric oxide bioavailability, and the number of endothelial progenitor cells, and also diminishes the level of inflammatory markers, namely pro-inflammatory cytokines and C-reactive protein. However, the mechanisms by which exercise improves endothelial function in coronary artery disease patients are not fully clarified. Several mechanisms have been proposed to explain the positive effect of exercise on the disease progression. They include the decrease in cytokine production by the adipose tissue, skeletal muscles, endothelial cells, and blood mononuclear cells, and also, the increase in the bioavailability of nitric oxide, antioxidant defences, and regenerative capacity of endothelium. This study aims to provide a critical review of the literature linking exercise, inflammation, and endothelial dysfunction in coronary artery patients, and to discuss the potential mechanisms behind the exercise-training improvement of endothelial function and inflammatory status.

Peptide-stimulation enhances compartmentalization and the catalytic activity of lung endothelial NOS

We reported that an 11 amino acid synthetic peptide (P1) activates lung endothelial cell nitric oxide synthase (eNOS) independent of its change in expression and/or phosphorylation. Since caveolae/eNOS dissociation is known to enhance the catalytic activity of eNOS, we examined whether P1-mediated increase of eNOS activity is associated with caveolae/cholesterol modulation, increased caveolin-1 phosphorylation, and intracellular compartmentalization of eNOS in pulmonary artery endothelial cells (PAEC). PAEC were incubated with or without (control) P1 or cholesterol modulators/caveolae disruptors, cholesterol oxidase (CHOX) and methyl-beta-cyclodextrin (CD), for 1 h at 37 degrees C. After incubation cells were used for: i) immunoprecipitation, ii) isolation of plasma membrane (PM)-, Golgi complex (GC)-, and non-Golgi complex (NGC)-enriched fractions, iii) immunofluorescence confocal imaging, and iv) electron microscopy for localization and/or eNOS activity. P1, CHOX, and CD-stimulation caused dissociation of eNOS from PM with increased localization to GC and/or NGC. P1 and CHOX significantly increased eNOS activity in PM and GC and CD-stimulation increased eNOS activity localized only in GC. P1 increased phosphorylation of caveolin-1 in intact cells and GC fraction. Immunofluorescence and/or immunogold labeled imaging/electron microscopy analysis of P1-, CHOX-, and CD-stimulated intact cells confirmed eNOS/caveolae dissociation and translocation of eNOS to GC. These results suggest that: i) P1-stimulation translocates eNOS to GC and enhances the catalytic activity of eNOS in both the PM and GC fractions of PAEC, ii) CHOX- but not CD-mediated caveolae and/or cholesterol modulation mimics the effect of P1-stimulated compartmentalization and activation of eNOS in PAEC, and iii) P1-stimulated caveolae/cholesterol modulation, phosphorylation of caveolin-1, and activation of eNOS is physiologically relevant since P1 is known to enhance NO/cGMP-dependent vasorelaxation in the pulmonary circulation.

Caveolin-1 mediates endotoxin inhibition of endothelin-1-induced endothelial nitric oxide synthase activity in liver sinusoidal endothelial cells

Endothelin-1 (ET-1) plays a key role in the regulation of endothelial nitric oxide synthase (eNOS) activation in liver sinusoidal endothelial cells (LSECs). In the presence of endotoxin, an increase in caveolin-1 (Cav-1) expression impairs ET-1/eNOS signaling; however, the molecular mechanism is unknown. The objective of this study was to investigate the molecular mechanism of Cav-1 in the regulation of LPS suppression of ET-1-mediated eNOS activation in LSECs by examining the effect of caveolae disruption using methyl-beta-cyclodextrin (CD) and filipin. Treatment with 5 mM CD for 30 min increased eNOS activity (+255%, P < 0.05). A dose (0.25 microg/ml) of filipin for 30 min produced a similar effect (+111%, P < 0.05). CD induced the perinuclear localization of Cav-1 and eNOS and stimulated NO production in the same region. Readdition of 0.5 mM cholesterol to saturate CD reversed these effects. Both the combined treatment with CD and ET-1 (CD + ET-1) and with filipin and ET-1 stimulated eNOS activity; however, pretreatment with endotoxin (LPS) abrogated these effects. Following LPS pretreatment, CD + ET-1 failed to stimulate eNOS activity (+51%, P > 0.05), which contributed to the reduced levels of eNOS-Ser1177 phosphorylation and eNOS-Thr495 dephosphorylation, the LPS/CD-induced overexpression and translocation of Cav-1 in the perinuclear region, and the increased perinuclear colocalization of eNOS with Cav-1. These results supported the hypothesis that Cav-1 mediates the action of endotoxin in suppressing ET-1-mediated eNOS activation and demonstrated that the manipulation of caveolae produces significant effects on ET-1-mediated eNOS activity in LSECs.

A high-cholesterol diet increases the association between caveolae and insulin receptors in rat liver

Caveolin-1, a component of caveolae, regulates signaling pathway compartmentalization by interacting with tyrosine (Tyr) kinase receptors and their substrates. Perturbations in caveolae lipid composition have been shown in vitro to displace proteins from lipid microdomains, thereby altering their functionality and subsequent downstream signaling. The role of caveolin-1 in insulin receptor (IR) signaling has been widely investigated in vitro mainly in 3T3-L1 adipocyte cells. However, in vivo experiments investigating this connection in liver tissue have not been carried out. The objective of the present study was to investigate the effects of a high-cholesterol diet on caveolin-1 expression and IR localization and activity in the rat liver. Compared with a standard diet, rats fed with diet rich in cholesterol significantly altered liver caveolae by increasing both caveolin-1 (66%, P < 0.05) and caveolin-2 (55%, P < 0.05) expression while caveolin-1 mRNA levels were reduced. Concomitantly, a 25% increase in localization of the caveolae-resident signaling protein IR was observed. The distribution of caveolar and noncaveolar phosphorylated IR was unaffected but insulin-induced IR activation was significantly enhanced following consumption of the high-cholesterol diet (120%, P < 0.001). However, the downstream molecules IRS-1 and Akt have shown impaired activity in cholesterol-fed rats suggesting insulin resistance condition. Insulin stimulation failed to induce Tyr phosphorylation of caveolin-1 in cholesterol-fed rats. These findings suggest a mechanism by which a high-cholesterol diet altered caveolin-1 expression in vivo accompanied by altered IR localization and activity.

Endothelial nitric oxide (NO) and its pathophysiologic regulation

Nitric oxide (NO) is a gaseous lipophilic free radical generated by three distinct isoforms of nitric oxide synthases (NOS), type 1 or neuronal (nNOS), type 2 or inducible (iNOS) and type 3 or endothelial NOS (eNOS). Expression of eNOS is altered in many types of cardiovascular disease, such as atherosclerosis, diabetes and hypertension. The ubiquitous chaperone heat shock protein 90 (hsp90) associates with NOS and is important for its proper folding and function. Current studies point toward a therapeutic potential by modulating hsp90-NOS association in various vascular diseases. Here we review the transcriptional regulation of endothelial NOS and factors affecting eNOS activity and function, as well as the important vascular pathologies associated with altered NOS function, focusing on the regulatory role of hsp90 and other factors in NO-associated pathogenesis of these diseases.

oxLDL facilitates flow-induced realignment of aortic endothelial cells

Alignment of vascular endothelial cells (ECs) in the direction of the flow is considered a key factor in maintaining endothelial integrity in an active hemodynamic environment. Our recent studies showed that exposure to oxidized LDL (oxLDL), one of the major proatherogenic lipoproteins, significantly increases the stiffness of human aortic ECs, suggesting that oxLDL may have a significant impact on the sensitivity of ECs to mechanical stimuli. In this study, we show that oxLDL strongly enhances the ability of ECs to realign in the direction of the flow and facilitates the formation of F-actin stress fibers under static and flow conditions. The impact of oxLDL on the flow-induced realignment is observed on whole cell and single-fiber levels. We also show that, similar to the effect of oxLDL on endothelial stiffness, the impact of oxLDL on flow-induced realignment can be simulated by methyl-beta-cyclodextrin-induced cholesterol depletion, supporting the hypothesis that oxLDL acts as cholesterol acceptor, rather than cholesterol donor, for ECs. Finally, we propose that oxLDL/cholesterol depletion-induced sensitization of ECs to flow may be a result of an increase in cellular stiffness and a respective increase in membrane-cytoskeleton tension.

Triglyceride-rich lipoprotein lipolysis increases aggregation of endothelial cell membrane microdomains and produces reactive oxygen species

Triglyceride-rich lipoprotein (TGRL) lipolysis may provide a proinflammatory stimulus to endothelium. Detergent-resistant plasma membrane microdomains (lipid rafts) have a number of functions in endothelial cell inflammation. The mechanisms of TGRL lipolysis-induced endothelial cell injury were investigated by examining endothelial cell lipid rafts and production of reactive oxygen species (ROS). Lipid raft microdomains in human aortic endothelial cells were visualized by confocal microscopy with fluorescein isothiocyanate-labeled cholera toxin B as a lipid raft marker. Incubation of Atto565-labeled TGRL with lipid raft-labeled endothelial cells showed that TGRL colocalized with the lipid rafts, TGRL lipolysis caused clustering and aggregation of lipid rafts, and colocalization of TGRL remnant particles on the endothelial cells aggregated lipid rafts. Furthermore, TGRL lipolysis caused translocation of low-density lipoprotein receptor-related protein, endothelial nitric oxide synthase, and caveolin-1 from raft regions to nonraft regions of the membrane 3 h after treatment with TGRL lipolysis. TGRL lipolysis significantly increased the production of ROS in endothelial cells, and both NADPH oxidase and cytochrome P-450 inhibitors reduced production of ROS. Our studies suggest that alteration of lipid raft morphology and composition and ROS production could contribute to TGRL lipolysis-mediated endothelial cell injury.

Caveolae and endothelial dysfunction: filling the caves in cardiovascular disease

Discovery in the early 1990s of caveolin-1, the structural protein responsible for maintaining the ohm shape of caveolae, greatly enhanced investigations to elucidate the role of these little caves in the plasma membrane. Perhaps one of the most important realizations concerning caveolae and caveolin is that these elements play an important functional role in the modulation of cell signal transduction pathways, including those involved in endothelial nitric oxide synthase (eNOS) function. Their role was confirmed by studies with caveolin-1 knockout mice which lack caveolae and display abnormal endothelial function responses. One limitation of these knockout models, however, is that absence of the caveolin protein not only results in the lack of caveolae as a structure but also in the lack of interaction/modulation of enzymes/molecules (e.g. eNOS) to which caveolin binds (whether in- or outside caveolae). In contrast to caveolin knockout models, recent experimental findings suggest that in certain cardiovascular diseases caveolin may dissociate from caveolae to the cytosol, hence decreasing the number of caveolae without a change in the total amount of caveolin. Therefore, as the importance of defining the role of caveolins both in caveolae and in cellular regions is being highlighted, it seems also important at the same time to further define the role of caveolae per se being present in the plasma membrane as a structural entity. The objective of this review is to make an explorative tour on the role of caveolae in vascular endothelial function based on existing literature together with some preliminary experimental findings. Evidence and arguments are put forward that alterations in endothelial caveolae do occur in cardiovascular disease and may contribute to the observed endothelial dysfunction in these conditions.

Caveolin-1 sensitizes vascular smooth muscle cells to mildly oxidized LDL-induced apoptosis

Oxidized low-density lipoprotein (oxLDL)-induced apoptosis of vascular cells may participate to plaque instability and rupture. Caveolin-1 has emerged as an important regulator of several signal transduction pathways and processes that play a role in atherosclerosis. In this study we examined the potential role of caveolin-1 in the regulation of oxLDL-induced Ca(2+) signaling and apoptosis in vascular smooth muscle cells (VSMC). Cells expressing caveolin-1 were more susceptible to oxLDL-induced apoptosis, and this was correlated with enhanced Ca(2+) entry and pro-apoptotic events. Moreover, caveolin-1 silencing by small interfering RNA decreased the level of apoptotic cells after oxLDL treatment. These findings provide new insights about the potential role of caveolin-1 in the regulation of oxLDL-induced apoptosis in vascular cells and its contribution to the instability of the plaque.

A Global Assessment of the Inflammatory Response Elicited Upon Open Abdominal Aortic Aneurysm Repair

The inflammatory response during elective open infrarenal abdominal aortic aneurysm repair and its impact on outcome is investigated. Twenty high-risk patients were enrolled, and blood samples were obtained at 8 perioperative time points. Endotoxin, cytokines (tumor necrosis factor-α and interleukin-1β, and interleukin-6), CD11b expression, and nitric oxide were measured. Peak endotoxin levels occurred within 30 minutes of reperfusion and were higher among patients developing complications. Interleukin-6 levels increased during reperfusion, reaching a peak on the first postoperative day. Interleukin-6 increase correlated with aortic clamp time and morbidity. CD11b expression increased 30 minutes after reperfusion, and this effect was greater among patients who developed complications. Endotoxin may be important in the pathogenesis of multiple organ dysfunction syndrome. Activated neutrophils may have a central role in tissue injury after reperfusion. Intraoperative CD11b upregulation may be an early marker for postoperative complications after infrarenal abdominal aortic aneurysm repair.

Endothelial arginase II: a novel target for the treatment of atherosclerosis

Oxidized low-density lipoproteins increase arginase activity and reciprocally decrease endothelial NO in human aortic endothelial cells. Here, we demonstrate that vascular endothelial arginase activity is increased in atherogenic-prone apolipoprotein E-null (ApoE(-/-)) and wild-type mice fed a high cholesterol diet. In ApoE(-/-) mice, selective arginase II inhibition or deletion of the arginase II gene (Arg II(-/-) mice) prevents high-cholesterol diet-dependent decreases in vascular NO production, decreases endothelial reactive oxygen species production, restores endothelial function, and prevents oxidized low-density lipoprotein-dependent increases in vascular stiffness. Furthermore, arginase inhibition significantly decreases plaque burden. These data indicate that arginase II plays a critical role in the pathophysiology of cholesterol-mediated endothelial dysfunction and represents a novel target for therapy in atherosclerosis.

Caveolae structure and function

Studies on the structure and function of caveolae have revealed how this versatile subcellular organelle can influence numerous signalling pathways. This brief review will discuss a few of the key features of caveolae as it relates to signalling and disease processes.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

Dynamic regulation of endothelial NOS mediated by competitive interaction with alpha-actinin-4 and calmodulin

Alpha-actinins are critical components of the actin cytoskeleton. Here we show that alpha-actinins serve another important biological function by binding to and competitively inhibiting calcium-dependent activation of endothelial NOS (eNOS). Alpha-actinin-2 was found to associate with eNOS in a yeast two-hybrid screen. In vascular endothelial cells, which only express alpha-actinin-1 and -4, alpha-actinin-4 interacted and colocalized with eNOS. Addition of alpha-actinin-4 directly inhibited eNOS recombinant protein, and overexpression of alpha-actinin-4 inhibited eNOS activity in eNOS-transfected COS-7 cells and bovine aortic endothelial cells (BAECs). In contrast, knockdown of alpha-actinin-4 by siRNA increased eNOS activity in BAECs. The alpha-actinin-4-binding site on eNOS was mapped to a central region comprising the calmodulin-binding domain, and the eNOS-binding site on alpha-actinin-4 was mapped to the fourth spectrin-like rod domain, R4. Treatment of endothelial cells with a calcium ionophore, A23187, decreased alpha-actinin-4-eNOS interaction, leading to translocation of alpha-actinin-4 from plasma membrane to cytoplasm. Indeed, addition of calmodulin displaced alpha-actinin-4 binding to eNOS and increased eNOS activity. These findings indicate that eNOS activity in vascular endothelial cells is tonically and dynamically regulated by competitive interaction with alpha-actinin-4 and calmodulin.

Diabetic HDL-associated myristic acid inhibits acetylcholine-induced nitric oxide generation by preventing the association of endothelial nitric oxide synthase with calmodulin

In the current study, we examined whether diabetes affected the ability of HDL to stimulate nitric oxide (NO) production. Using HDL isolated from both diabetic humans and diabetic mouse models, we found that female HDL no longer induced NO synthesis, despite containing equivalent amounts of estrogen as nondiabetic controls. Furthermore, HDL isolated from diabetic females and males prevented acetylcholine-induced stimulation of NO generation. Analyses of both the human and mouse diabetic HDL particles showed that the HDLs contained increased levels of myristic acid. To determine whether myristic acid associated with HDL particles was responsible for the decrease in NO generation, myristic acid was added to HDL isolated from nondiabetic humans and mice. Myristic acid-associated HDL inhibited the generation of NO in a dose-dependent manner. Importantly, diabetic HDL did not alter the levels of endothelial NO synthase or acetylcholine receptors associated with the cells. Surprisingly, diabetic HDL inhibited ionomycin-induced stimulation of NO production without affecting ionomycin-induced increases in intracellular calcium. Further analysis indicated that diabetic HDL prevented calmodulin from interacting with endothelial NO synthase (eNOS) but did not affect the activation of calmodulin kinase or calcium-independent mechanisms for stimulating eNOS. These studies are the first to show that a specific fatty acid associated with HDL inhibits the stimulation of NO generation. These findings have important implications regarding cardiovascular disease in diabetic patients.

Transport-dependent calcium signaling in spatially segregated cellular caveolar domains

We developed a two-dimensional model of transport-dependent intracellular calcium signaling in endothelial cells (ECs). Our purpose was to evaluate the effects of spatial colocalization of endothelial nitric oxide synthase (eNOS) and capacitative calcium entry (CCE) channels in caveolae on eNOS activation in response to ATP. Caveolae are specialized microdomains of the plasma membrane that contain a variety of signaling molecules to optimize their interactions and regulate their activity. In ECs, these molecules include CCE channels and eNOS. To achieve a quantitative understanding of the mechanisms of microdomain calcium signaling and the preferential sensitivity of eNOS to calcium entering the cell through CCE channels, we constructed a mathematical model incorporating the cell morphology and cellular physiological processes. The model predicts that the spatial segregation of calcium channels in ECs can create transport-dependent sharp gradients in calcium concentration within the cell. The calcium concentration gradient is affected by channel density and cell geometry. This transport-dependent calcium signaling specificity effect is enhanced in ECs by increasing the spatial segregation of the caveolar signaling domains. Our simulation significantly advances the understanding of how Ca2+, despite its many potential actions, can mediate selective activation of signaling pathways. We show that diffusion-limited calcium transport allows functional compartmentalization of signaling pathways based on the spatial arrangements of Ca2+ sources and targets.

Endothelial dysfunction and improvement of the angiotensin II-reactivity in hypercholesterolemic rabbits: role of cyclooxygenase metabolites

The aim of this paper was to study the effect of high cholesterol diet on endothelial function and vascular reactivity to angiotensin II and to test the role of vasoconstrictor cyclooxygenase metabolites in this experimental condition. Rabbits were fed with either normal chow or a diet containing 1% cholesterol for 6-7-week. Isometric contractions were measured in rubbed or unrubbed aortic rings. Arteries were contracted with noradrenaline and then exposed to one cumulative dose-response curve to acetylcholine in absence (control) or in presence of indomethacin, (N-[2-cyvlohexyloxy)-4-nitrophenyl]-methanesulfonamide) (NS 398) or 4-hydroxy-2,2,6,6-tetraethylpiperidine-N-oxyl (tempol). After washing the arteries, one cumulative dose-response curve to angiotensin II was constructed in absence or presence of indomethacin, NS 398, [1S-[1 alpha,2 beta (5Z),3 beta,4 alpha]-7-[3-[[2-[(phenylamino) carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1] hept-2-yl]-5-heptenoic acid (SQ29548) or 17-octadecynoic acid (17-ODYA). In other group, resting potential was recorded in basal and angiotensin II-stimulated conditions. Indomethacin, NS 398 or 17-ODYA were added to the bath before angiotensin II-stimulation. Rabbits fed on a diet enriched with cholesterol showed higher plasma levels of total cholesterol and LDL. Hypercholesterolemic diet impaired acetylcholine relaxation. Indomethacin normalized endothelium-dependent relaxation whereas NS 398 and tempol had no effect on this phenomenon. Angiotensin II-reactivity was increased in endothelium intact hypercholesterolemic aortic rings and indomethacin, SQ29548 or 17-ODYA blocked this effect. The resting potential of unrubbed hypercholesterolemic arteries was significantly less negative to control after angiotensin II-stimulation. 17-ODYA but not indomethacin prevented angiotensin II-depolarization. High cholesterol diet caused endothelial dysfunction and increased the angiotensin II-reactivity. Both effects were cyclooxygenase1-dependent. Deficit in the NO-production might improve 20-hydroxyeicosatrienoic acid availability, which induces depolarization and angiotensin II-sensitization. In addition, 20-hydroxyeicosatrienoic acid would be metabolized by cyclooxygenase1 to 20-endoperoxides which act through thromboxane A(2)/prostaglandin H(2) receptors contributing to angiotensin II-reactivity increase.

Endothelial function, arterial stiffness and lipid lowering drugs

The endothelium is a dynamic organ that plays a pivotal role in cardiovascular homeostasis. Alteration in endothelial function precedes the development of atherosclerosis and contributes to its initiation, perpetuation and clinical manifestations. It has been suggested that the assessment of endothelial function could represent a barometer of vascular health that could be used to gauge cardiovascular risk. This review summarises the various methods used to assess endothelium-dependent vasodilatation and their potential prognostic implications. In addition, the techniques used to evaluate arterial stiffness are discussed. The latter is to some extent controlled by the endothelium and has been the subject of considerable research in recent years. This paper also discusses the effects of lipid lowering treatment on both endothelial function and arterial stiffness.

Role of redox regulation and lipid rafts in macrophages during Ox-LDL-mediated foam cell formation

Hyperlipidemias and small dense LDLs in patients with high-triglyceride low-HDL syndromes lead to a prolonged half life of apoB-containing particles. This is associated with reactive oxygen species (ROS) activation and leads to formation of oxidized LDL (Ox-LDL). Generators of ROS in macrophages (MACs) include myeloperoxidase (MPO)-mediated respiratory burst and raft-associated NADPH-oxidase. The intracellular oxidant milieu is involved in cellular signaling pathways, like ion-transport systems, protein phosphorylation, and gene expression. Lipid oxidation through ROS can amplify foam cell formation through Ox-LDL uptake, leading to formation of ceramide (Cer)-rich lipid membrane microdomains, and is associated with expansion of the lysosomal compartment and an upregulation of ABCA1 and other genes of the AP3 secretory pathway. Ox-LDL may also affect cell-surface turnover of Cer-backbone sphingolipids and apoE-mediated uptake by LRP-family members. In contrast, HDL-mediated lipid efflux causes disruption of lipid membrane microdomains and prevents foam cell formation. Oxidation of HDL through MPO leads to a failure of lipid efflux and enhancement of MAC loading. Therefore, lipid rafts and oxidation processes are important in regulation of MAC foam cell formation and atherosclerosis, and the balance between oxidant and antioxidant intracellular systems is critically important for efficient MAC function.

Lipid rafts in membrane-cytoskeleton interactions and control of cellular biomechanics: actions of oxLDL

Membrane-cytoskeleton coupling is known to play major roles in a plethora of cellular responses, such as cell growth, differentiation, polarization, motility, and others. In this review, the authors discuss the growing amount of evidence indicating that membrane-cytoskeleton interactions are regulated by the lipid composition of the plasma membrane, suggesting that cholesterol-rich membrane domains (lipid rafts), including caveolae, are essential for membrane-cytoskeleton coupling. Several models for raft-cytoskeleton interactions are discussed. Also described is the evidence suggesting that raft-cytoskeleton interactions play key roles in several cytoskeleton-dependent processes, particularly in the regulation of cellular biomechanical properties. To address further the physiological significance of raft-cytoskeleton coupling, the authors focus on the impact of oxidized low density lipoproteins, one of the major cholesterol carriers and proatherogenic factors, on the integrity of lipid rafts/caveolae, and on the organization of the cytoskeleton. Finally, the authors review the recent studies showing that oxLDL and cholesterol depletion have similar impacts on the biomechanical properties of vascular endothelial cells, which in turn affect endothelial angiogenic potential.

Attenuated Expression of Profilin-1 Confers Protection From Atherosclerosis in the LDL Receptor–Null Mouse

Atherosclerosis-related events are a major cause of morbidity and death worldwide, but the mechanisms underlying atherogenesis are not fully understood. We showed in previous studies that the actin-binding protein profilin-1 (pfn) was upregulated in atherosclerotic plaques and in endothelial cells (ECs) treated with oxidized low-density lipoproteins (oxLDL). The present study addressed the role of pfn in atheroma formation. To this end, mice with heterozygous deficiency of pfn, Pfn +/− , were crossed with Ldlr −/− mice. After 2 months under a 1.25% cholesterol atherogenic diet, Pfn +/− Ldlr −/− (PfnHet) exhibited a significant reduction in lesion burden compared with Ldlr −/− control mice (PfnWT), whereas total cholesterol and triglyceride levels were similar in the 2 groups. Relevant atheroprotective changes were identified in PfnHet. When compared with PfnWT, aortas from PfnHet mice showed preserved endothelial nitric oxide synthase (eNOS) activation and nitric oxide (NO)-dependent signaling, and reduced vascular cell adhesion molecule (VCAM)-1 expression and macrophage accumulation at lesion-prone sites. Similarly, knockdown of pfn in cultured aortic ECs was protective against endothelial dysfunction triggered by oxLDL. Finally, bone marrow–derived macrophages from PfnHet showed blunted internalization of oxLDL and oxLDL-induced inflammation. These studies demonstrate that pfn levels modulate processes critical for early atheroma formation and suggest that pfn heterozygosity confers atheroprotection through combined endothelial- and macrophage-dependent mechanisms.

The effect of cellular cholesterol on membrane-cytoskeleton adhesion

Whereas recent studies suggest that cholesterol plays important role in the regulation of membrane proteins, its effect on the interaction of the cell membrane with the underlying cytoskeleton is not well understood. Here, we investigated this by measuring the forces needed to extract nanotubes (tethers) from the plasma membrane, using atomic force microscopy. The magnitude of these forces provided a direct measure of cell stiffness, cell membrane effective surface viscosity and association with the underlying cytoskeleton. Furthermore, we measured the lateral diffusion constant of a lipid analog DiIC12, using fluorescence recovery after photobleaching, which offers additional information on the organization of the membrane. We found that cholesterol depletion significantly increased the adhesion energy between the membrane and the cytoskeleton and decreased the membrane diffusion constant. An increase in cellular cholesterol to a level higher than that in control cells led to a decrease in the adhesion energy and the membrane surface viscosity. Disassembly of the actin network abrogated all the observed effects, suggesting that cholesterol affects the mechanical properties of a cell through the underlying cytoskeleton. The results of these quantitative studies may help to better understand the biomechanical processes accompanying the development of atherosclerosis.

Disruption of endothelial caveolae is associated with impairment of both NO- as well as EDHF in acetylcholine-induced relaxation depending on their relative contribution in different vascular beds

Caveolae represent an important structural element involved in endothelial signal-transduction. The present study was designed to investigate the role of caveolae in endothelium-dependent relaxation of different vascular beds. Caveolae were disrupted by cholesterol depletion with filipin (4x10(-6) g L(-1)) or methyl-beta-cyclodextrin (MCD; 1x10(-3) mol L(-1)) and the effect on endothelium-dependent relaxation was studied in rat aorta, small renal arteries and mesenteric arteries in the absence and presence of L-NMMA. The contribution of NO and EDHF, respectively, to total relaxation in response to acetylcholine (ACh) gradually changed from aorta (71.2+/-6.1% and 28.8+/-6.1%), to renal arteries (48.6+/-6.4% and 51.4+/-6.4%) and to mesenteric arteries (9.1+/-4.0% and 90.9+/-4.1%). Electron microscopy confirmed filipin to decrease the number of endothelial caveolae in all vessels studied. Incubation with filipin inhibited endothelium-dependent relaxation induced by cumulative doses of ACh (3x10(-9)-10(-4) mol L(-1)) in all three vascular beds. In aorta, treatment with either filipin or MCD only inhibited the NO component, whereas in renal artery both NO and EDHF formation were affected. In contrast, in mesenteric arteries, filipin treatment only reduced EDHF formation. Disruption of endothelial caveolae is associated with the impairment of both NO and EDHF in acetylcholine-induced relaxation.

Inability of HDL from abdominally obese subjects to counteract the inhibitory effect of oxidized LDL on vasorelaxation

Abdominal obesity is associated with a decreased plasma concentration of HDL cholesterol and with qualitative modifications of HDL, such as triglyceride enrichment. Our aim was to determine, in isolated aorta rings, whether HDL from obese subjects can counteract the inhibitory effect of oxidized low density lipoprotein (OxLDL) on endothelium-dependent vasodilation as efficiently as HDL from normolipidemic, lean subjects. Plasma triglycerides were 74% higher (P < 0.005) in obese subjects compared with controls, and apolipoprotein A-I (apoA-I) and HDL cholesterol concentrations were 12% and 17% lower (P < 0.05), respectively. HDL from control subjects significantly reduced the inhibitory effect of OxLDL on vasodilation [maximal relaxation (E(max)) = 82.1 +/- 8.6% vs. 54.1 +/- 8.1%; P < 0.0001], but HDL from obese subjects had no effect (E(max) = 47.2 +/- 12.5% vs. 54.1 +/- 8.1%; NS). In HDL from abdominally obese subjects compared with HDL from controls, the apoA-I content was 12% lower (P < 0.05) and the triglyceride-to-cholesteryl ester ratio was 36% higher (P = 0.08)). E(max)(OxLDL + HDL) was correlated with HDL apoA-I content and triglyceride-to-cholesteryl ester ratio (r = 0.36 and r = -0.38, respectively; P < 0.05). We conclude that in abdominally obese subjects, the ability of HDL to counteract the inhibitory effect of OxLDL on vascular relaxation is impaired. This could contribute to the increased cardiovascular risk observed in these subjects.

Mechanism of the Antithrombotic Effect of Dietary Diacylglycerol in Atherogenic Mice

INTRODUCTION

We have shown earlier that diacylglycerol (DAG) but not triacylglycerol (TAG) inhibited thrombus formation. The aim of the present study was to investigate the mechanism of this antithrombotic effect of DAG.

MATERIALS AND METHODS

Four different diets, the (1) Western-style high-fat diet (HFD) containing 20% lipid and 0.05% cholesterol (w/w), (2) TAG-rich and (3) DAG-rich HFDs containing 20% lipid and 0.05% cholesterol, but all lipid replaced by TAG or DAG oil with very similar fatty acid composition and the (4) Japanese-style low-fat diet (LFD) containing 7% oil but no cholesterol were given to apolipoprotein E and low-density lipoprotein (LDL) receptor double-deficient mice. Atherogenicity was assessed by morphology, mapping the whole aorta and measuring the total area of lipid-stained lesions. Endothelial function was measured by the flow-mediated vasodilation test. Platelet reactivity was assessed from native blood sample by a shear-induced platelet function test (hemostatometry). Serum lipoprotein profile was measured by HPLC.

RESULTS

Both the Western-style and the TAG-rich HFDs have accelerated atherosclerosis. In contrast, DAG-rich HFD inhibited the atherosclerotic process to an extent comparable with the Japanese-style LFD. There was no significant difference in platelet and coagulant activity between the studied diet groups. DAG-rich but not the TAG-rich HFD significantly suppressed serum LDL cholesterol level.

CONCLUSIONS

The present findings suggest that the mechanism of antithrombotic and anti-atherogenic effect of DAG may involve the protection of the vascular endothelium from injury and lowered serum LDL cholesterol.

Eicosapentaenoic acid modifies lipid composition in caveolae and induces translocation of endothelial nitric oxide synthase

Endothelial nitric oxide synthase (eNOS) plays a crucial role in the regulation of a variety of cardiovascular functions. Many studies have shown that dietary n-3 polyunsaturated fatty acids (PUFAs) have beneficial effects on coronary atherosclerosis. However, the mechanisms of n-3 PUFAs regulation in eNOS activation remain unknown. In the present study we investigated the effects of eicosapentaenoic acid (EPA, 20:5 n-3) on subcellular distribution of eNOS and lipid composition of caveolae. We demonstrated for the first time that EPA treatment profoundly altered lipid composition and fatty acyl substitutions of phospholipids in caveolae. We found that caveolin-1 was solely located in caveolae fractions in control cells, and EPA treatment displaced caveolin-1 from caveolae. eNOS was detected in the caveolin-enriched fractions and noncaveolae fractions in control cells. EPA treatment induced the translocation of eNOS from caveolae fractions to soluble fractions. P-eNOS was also distributed in both fractions. After EPA treatment, the level of p-eNOS in each fraction was increased but the distribution of which was unaffected. Moreover, the results of immunofluorescence confirmed that EPA could redistribute caveolin-1 and eNOS in plasma membrane. eNOS activity in HUVEC cells was increased after EPA treatment, which was in a dose dependent manner. And incubation with 50 microM EPA had the maximum effect on eNOS activity. Our results suggested that eNOS translocation was paralleled by a stimulated capacity for NO production in the cells. We found that total Akt and p-Akt were primarily presented in heavy membranes in control cells, and the relative level of p-Akt increased but the distribution did not change after EPA treatment. The distribution of CaM was slightly changed after EPA treatment. Our results indicated that n-3 PUFAs profoundly altered caveolae microenvironment, thereby modifying location and function of proteins in caveolae. EPA-induced alterations of lipid and proteins in caveolae may be an important mechanism in the pathophysiologic process of atherosclerosis.