High-density lipoprotein antagonizes oxidized low-density lipoprotein by suppressing oxygen free-radical formation and preserving nitric oxide bioactivity (original) (raw)
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2001
Oxidized low density lipoprotein (ox-LDL) has been suggested to affect endothelium-dependent vascular tone through a decreased biological activity of endothelium-derived nitric oxide (NO). Oxidative inactivation of NO is regarded as an important cause of its decreased biological activity, and in this context superoxide (O 2 .) is known to inactivate NO in a chemical reaction during which peroxynitrite is formed. In this study we examined the effect of ox-LDL on the intracellular NO concentration in bovine aortic endothelial cells and whether this effect is influenced by ox-LDL binding to the endothelial receptor lectin-like ox-LDL receptor-1 (LOX-1) through the formation of reactive oxygen species and in particular of O 2. . ox-LDL induced a significant dose-dependent decrease in intracellular NO concentration both in basal and stimulated conditions after less than 1 min of incubation with bovine aortic endothelial cells (p < 0.01). In the same experimental conditions ox-LDL also induced O 2. generation (p < 0.001). In the presence of radical scavengers and anti-LOX-1 monoclonal antibody, O 2. formation induced by ox-LDL was reduced (p < 0.001) with a contemporary rise in intracellular NO concentration (p < 0.001). ox-LDL did not significantly modify the ability of endothelial nitric oxide synthase to metabolize L-arginine to L-citrulline. The results of this study show that one of the pathophysiological consequences of ox-LDL binding to LOX-1 may be the inactivation of NO through an increased cellular production of O 2. . Endothelium-dependent relaxation is impaired in animals with atherosclerosis (1-3), which has been linked to a decreased production and/or biological activity of endotheliumderived nitric oxide (NO) 1 (4, 5). Oxidative inactivation of NO is
International Journal of Molecular Sciences, 2019
The maintenance of physiological levels of nitric oxide (NO) produced by eNOS represents a key element for vascular endothelial homeostasis. On the other hand, NO overproduction, due to the activation of iNOS under different stress conditions, leads to endothelial dysfunction and, in the late stages, to the development of atherosclerosis. Oxidized LDLs (oxLDLs) represent the major candidates to trigger biomolecular processes accompanying endothelial dysfunction and vascular inflammation leading to atherosclerosis, though the pathophysiological mechanism still remains to be elucidated. Here, we summarize recent evidence suggesting that oxLDLs produce significant impairment in the modulation of the eNOS/iNOS machinery, downregulating eNOS via the HMGB1-TLR4-Caveolin-1 pathway. On the other hand, increased oxLDLs lead to sustained activation of the scavenger receptor LOX-1 and, subsequently, to NFkB activation, which, in turn, increases iNOS, leading to EC oxidative stress. Finally, th...
HDL and endothelial protection
British Journal of Pharmacology, 2013
High-density lipoproteins (HDLs) represent a family of particles characterized by the presence of apolipoprotein A-I (apoA-I) and by their ability to transport cholesterol from peripheral tissues back to the liver. In addition to this function, HDLs display pleiotropic effects including antioxidant, anti-apoptotic, anti-inflammatory, anti-thrombotic or anti-proteolytic properties that account for their protective action on endothelial cells. Vasodilatation via production of nitric oxide is also a hallmark of HDL action on endothelial cells. Endothelial cells express receptors for apoA-I and HDLs that mediate intracellular signalling and potentially participate in the internalization of these particles. In this review, we will detail the different effects of HDLs on the endothelium in normal and pathological conditions with a particular focus on the potential use of HDL therapy to restore endothelial function and integrity.
2000
Background-Native and oxidized LDLs (n-LDL and ox-LDL) are involved in the atherogenic process and affect endothelium-dependent vascular tone through their interaction with nitric oxide (NO). Methods and Results-In this study we evaluated directly, by using a porphyrinic microsensor, the effect of increasing lipoprotein concentrations on endothelial NO and superoxide (O 2 Ϫ ) production. We investigated where lipoproteins may affect the L-arginine-NO pathway by pretreating cells with L-arginine, L-N-arginine methyl ester (L-NAME), and superoxide dismutase. Bovine aortic endothelial cells were exposed for 1 hour to increasing concentrations of n-LDL (from 0 to 240 mg cholesterol/dL) and ox-LDL (from 0 to 140 mg cholesterol/dL). A stimulated (calcium ionophore) NO concentration decreased to 29% of the control at n-LDL concentration of 80 mg cholesterol/dL and to 15% of the control at 20 mg cholesterol/dL of ox-LDL. L-Arginine partially neutralized the inhibitory effect of n-LDL and ox-LDL on the NO generation. Superoxide dismutase pretreatment did not modify NO production, whereas L-NAME blunted NO generation at all LDL concentrations. O 2 Ϫ production was increased at low n-LDL and very low ox-LDL concentrations; this was reversed by L-arginine. Conclusions-These findings confirm the inhibitory role of n-LDL and ox-LDL on NO generation and suggest that lipoproteins may induce a decreased uptake of L-arginine. The local depletion of the L-arginine substrate may derange the NO synthase, leading to overproduction of O 2 Ϫ from oxygen, the other substrate of NO synthase. (Circulation.
Journal of Biological Chemistry, 2003
High density lipoprotein (HDL) activates endothelial nitric oxide synthase (eNOS), leading to increased production of the antiatherogenic molecule NO. A variety of stimuli regulate eNOS activity through signaling pathways involving Akt kinase and/or MAP kinase. In the present study we investigated the role of kinase cascades in HDL-induced eNOS stimulation in cultured endothelial cells and COS M6 cells transfected with eNOS and the HDL receptor, scavenger receptor B-I (SR-BI). HDL (10-50 µg/ml, 20 min) caused eNOS phosphorylation at Ser-1179, and dominant negative Akt inhibited both HDL-mediated phosphorylation and activation of the enzyme. PI3 kinase inhibition or dominant negative PI3 kinase also blocked the phosphorylation and activation of eNOS by HDL. Studies with genistein and PP2 showed that the non-receptor tyrosine kinase, src, is an upstream stimulator of the PI3 kinase-Akt pathway in this paradigm. In addition, HDL activated MAP kinase through PI3 kinase, and MEK inhibition fully attenuated eNOS stimulation by HDL without affecting Akt or eNOS Ser-1179 phosphorylation. Conversely, dominant negative Akt did not alter HDL-induced MAP kinase activation. These results indicate that HDL stimulates eNOS through common upstream, src-mediated signaling which leads to parallel activation of Akt and MAP kinases and their resultant independent modulation of the enzyme. by guest on June 4, 2016 http://www.jbc.org/ Downloaded from Recently Li and colleagues also reported that HDL binding to SR-BI activates eNOS (5). The HDL-induced increase in NO production may be critical to the atheroprotective features of HDL since diminished bioavailablity of endotheliumderived NO has a key role in the early pathogenesis of hypercholesterolemiainduced vascular disease and atherosclerosis (6-8). However, the mechanisms by which HDL activates eNOS are yet to be clarified. eNOS is one of three isoenzymes which convert L-arginine to L-citrulline plus NO. The activity of eNOS is regulated by complex signal transduction pathways that involve various phosphorylation events and protein-protein interactions. Many stimuli modulate eNOS activity by activating kinases which alter the phosphorylation of the enzyme (9-15). Akt kinase (also known as PKB) by guest on June 4, 2016 http://www.jbc.org/ Downloaded from activates eNOS by directly phosphorylating the enzyme at serine-1179 (Ser-1179) (19). Akt itself is phosphorylated and activated by phosphoinositide 3kinase (PI3 kinase), which in turn is activated by a tyrosine kinase (TK). Both receptor TK and non-receptor TK are involved in PI3 kinase-Akt mediated eNOS activation by various agonists . In contrast to Ser-1179, phosphorylation of threonine-497 (Thr-497) of eNOS attenuates enzyme activity . eNOS is also modulated by MAP kinases (23,24) and unlike Akt, the effect of MAP kinases on eNOS activity can be either positive or negative (9,25-27). The role of kinase cascades in signaling by HDL from SR-BI to eNOS is entirely unknown.
2018
The release of nanomolar concentrations of nitric oxide (NO) by endothelial cells (EC), via activation of constitutive NO synthase (eNOS), represents the pre-requisite for the vaso-protective role of vascular endothelium. On the other hand, exaggerated release of NO as a consequence of activation of inducible NO synthase (iNOS), leads to endothelial dysfunction and, at the late stages, to the development of atherothrombosis. Oxidyzed LDLs (OxyLDL) represent the major candidate to trigger biomolecular processes accompanying endothelial dysfunction and vascular inflammation leading to atherosclerosis development though the pathophysiological mechanism still remains to be elucidated. Here, we summarize recent evidence suggesting that oxyLDL produce significant impairment in the balance in the eNOS/iNOS machinery, downregulating eNOS via HMGB1-TLR4-Caveolin-1 pathway. On the other hand, a sustained activation of the scavenger receptor LOX-1 leads to NFkB activation which, in turn, incre...
15-Lipoxygenase-Mediated Modification of HDL3 Impairs eNOS Activation in Human Endothelial Cells
Lipids, 2014
Caveolae are cholesterol and glycosphingolipidsenriched microdomains of plasma membranes. Caveolin-1 represents the major structural protein of caveolae, that also contain receptors and molecules involved in signal transduction pathways. Caveolae are particularly abundant in endothelial cells, where they play important physiological and pathological roles in regulating endothelial cell functions. Several molecules with relevant functions in endothelial cells are localized in caveolae, including endothelial nitric oxide synthase (eNOS), which regulates the production of nitric oxide, and scavenger receptor class B type I (SR-BI), which plays a key role in the induction of eNOS activity mediated by high density lipoproteins (HDL). HDL have several atheroprotective functions, including a positive effect on endothelial cells, as it is a potent agonist of eNOS through the interaction with SR-BI. However, the oxidative modification of HDL may impair their protective role. In the present study we evaluated the effect of 15-lipoxygenasemediated modification of HDL 3 on the expression and/or activity of some proteins localized in endothelial caveolae and involved in the nitric oxide generation pathway. We found that after modification, HDL 3 failed to activate eNOS and to induce NO production, due to both a reduced ability to interact with its own receptor SR-BI and to a reduced expression of SR-BI in cells exposed to modified HDL. These findings suggest that modification of HDL may reduce its endothelial-protective role also by interfering with vasodilatory function of HDL. Keywords High density lipoprotein Á Endothelial cells Á 15-Lipoxygenase Á Caveolae Á Nitric oxide Abbreviations 15LO 15-Lipoxygenase ABCG1 ATP binding cassette transporter G1 CAV-1 Caveolin-1 eNOS Endothelial nitric oxide synthase HDL High density lipoprotein HUVEC Human umbilical vein endothelial cell(s) LOX-1 Lectin-like oxidized low-density lipoprotein receptor-1 MAPK Mitogen-activated protein kinase NO Nitric oxide S1P3
Vascular Health and Risk Management, 2005
In addition to their role in reverse cholesterol transport, high-density lipoproteins (HDL) exert several beneficial effects, including the prevention and correction of endothelial dysfunction. HDL promote endothelium proliferation and diminish endothelial apoptosis; they play a key role in vasorelaxation by increasing the release of nitric oxide and prostacyclin through the induction of the expression and the activity of endothelial nitric oxide synthase and the coupling of cyclooxygenase 2 and prostacyclin synthase. In addition, HDL affect coagulation, fibrynolisis, platelet adhesion, adhesion molecules, and protease expression, and they exert antioxidant activity. These effects are achieved at the gene expression level and are dependent on the activation of several intracellular signaling pathways, including PI3K/Akt, ERK1/2, PKC, and p38MAPK. The complexity of the signaling pathways modulated by HDL reflects the different effects of the components of this class of lipoproteins such as apolipoproteins or lipids on endothelial cell gene expression and the subsequent modulation of endothelial function observed. The in vivo relevance of these findings to endothelial recovery during physiological or pathological conditions remains to be addressed; nevertheless, the results of clinical studies with synthetic HDL, ApoA-I mimetics, and drugs that are becoming available that selectively affect HDL plasma levels and biological functions support the importance of the correction of endothelial function by HDL.
British Journal of Pharmacology, 1992
The mechanism by which Cu2f-oxidized low-density lipoproteins (oxLDL) inhibit acetylcholine (ACh)-evoked relaxations mediated by endothelium-derived nitric oxide (EDRF) in rabbit aortic rings was investigated. The proposed role of lysophosphatidylcholine (LPC) in the inhibition was also studied. 2 The kinetics of lipid peroxidation of native low-density lipoproteins (LDL) from individual donors, as measured by changes in conjugated diene concentration, were related to the inhibitory effects of the resultant oxLDL. It was found that the more susceptible LDL was to oxidation, the greater the inhibition. 3 No correlation was found between the inhibitory effects of oxLDL and LPC content. 4 Synthetic 1-palmitoyl LPC produced an inhibition of ACh-induced relaxations and when added to precontracted rings evoked nitric oxide-mediated endothelium-dependent relaxation. This latter effect was not elicited by oxLDL. 5 Synthetic 1-palmitoyl (10 uM) had no effect on relaxations evoked by glyceryl trinitrate in endothelium-denuded aortic rings in contrast to the inhibition found previously for oxLDL. 6 Concentrations of oxLDL and phospholipase A2-treated LDL which inhibited relaxation contained very different LPC concentrations. Unlike oxLDL, the inhibitory effects of phospholipase A2-treated LDL preparations were independent of the donors and showed no lag period. 7 We sugggest that there are differences in the mechanisms by which oxLDL and 1-palmitoyl LPC exert their inhibitory effects on relaxation. 8 The inhibition of relaxation by oxLDL (1-2 mg protein ml-1) was prevented by the presence of high-density lipoproteins (HDL; 1-2 mg protein ml-1). 9 It is proposed that prevention of the inhibition of relaxation by HDL is consistent with the inhibitory factor(s) being lipophilic constituents of oxLDL. However, variations in the inhibitory effects of oxLDL preparations are not due to differences in their LPC content and factors other than LPC must contribute to the inhibition.