oxLDL-induced Endothelial Dysfunction Research Articles

Tripeptide Leu-Ser-Trp Regulates the Vascular Endothelial Cells Phenotype Switching by Mediating the Vascular Smooth Muscle Cells-Derived Small Extracellular Vesicles Packaging of miR-145.

Tripeptide LSW, initially identified as a potent ACE inhibitory peptide from soybean protein, was recently reported to exert a protective effect against angiotensin II-induced endothelial dysfunction via extracellular vesicles (EVs). However, the molecular mechanisms, especially in lipid accumulation-induced atherosclerosis, still remain unclear. The study aimed to investigate whether the protective effects of LSW against endothelial dysfunction on vascular endothelial cells (VECs) was via vascular smooth muscle cells (VSMCs)-derived miRNA-145 packaged in EVs. The miRNA-145 was concentrated in EVs from LSW-treated VSMCs (LEVs), internalized into the HVUECs, and targeted the programmed cell death protein 4 (PDCD4) expression of HUVECs. Oxidized low-density lipoprotein (oxLDL) was applied to induce endothelial dysfunction in HUVECs; oxLDL-induced endothelial dysfunction in HUVECs was attenuated by PDCD4 knockout or LEVs incubation. The results of this study suggested a novel function of LSW as a regulator on the functional EVs from vascular cells in the oxLDL-induced atherosclerotic model.

LDL receptors, caveolae and cholesterol in endothelial dysfunction: oxLDLs accomplices or victims?

Oxidized LDLs (oxLDLs) and oxysterols play a key role in endothelial dysfunction and the development of atherosclerosis. The loss of vascular endothelium function negatively impacts vasomotion, cell growth, adhesiveness and barrier functions. While for some of these disturbances, a reasonable explanation can be provided from a mechanistic standpoint, for many others, the molecular mediators that are involved are unknown. Caveolae, specific plasma membrane domains, have recently emerged as targets and mediators of oxLDL-induced endothelial dysfunction. Caveolae and their associated protein caveolin-1 (Cav-1) are involved in oxLDLs/LDLs transcytosis, mainly through the scavenger receptor class B type 1 (SR-B1 or SCARB1). In contrast, oxLDLs endocytosis is mediated by the lectin-like oxidized LDL receptor 1 (LOX-1), whose activity depends on an intact caveolae system. In addition, LOX-1 regulates the expression of Cav-1 and vice versa. On the other hand, oxLDLs may affect cholesterol plasma membrane content/distribution thus influencing caveolae architecture, Cav-1 localization and the associated signalling. Overall, the evidence indicate that caveolae have both active and passive roles in oxLDL-induced endothelial cell dysfunction. First, as mediators of lipid uptake and transfer in the subendothelial space and, later, as targets of changes in composition/dynamics of plasma membrane lipids resulting from increased levels of circulating oxLDLs. Gaining a better understanding of how oxLDLs interact with endothelial cells and modulate caveolae-mediated signalling pathways, leading to endothelial dysfunction, is crucial to find new targets for intervention to tackle atherosclerosis and the related clinical entities. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Salvianolic acid B protects against oxLDL-induced endothelial dysfunction under high-glucose conditions by downregulating ROCK1-mediated mitophagy and apoptosis

Diabetes is related to alterations in glucose and lipid metabolism, which are linked to endothelial cell (EC) dysfunction. Salvianolic acid B (Sal B), one of the major ingredient of Danshen (Salvia miltiorrhiza), possesses many of the biological activities. However, protective effect of Sal B against oxLDL induced ECs dysfunction under high glucose condition (high Glu) is not well known. Thus, in this study, we investigated the protective effects of Sal B against EC dysfunction induced by oxLDL and high Glu and examined the associated mechanisms. Our results showed that Sal B significantly and dose-dependently decreased oxLDL- and high Glu–mediated induction of lectin-like oxLDL receptor-1 and significantly decreased oxLDL- and high Glu–induced mitochondrial ROS (mtROS) production and mitochondrial DNA (mtDNA) expression. In addition, oxLDL stimulation under high-Glu conditions activated the intrinsic apoptosis pathway in ECs. These effects were abolished by Sal B through reductions in mtROS and mtDNA. Furthermore, Sal B inhibited oxLDL- and high Glu–induced increases in fission protein (p-DRP 1 and FIS 1) levels. OxLDL and high Glu activated the ROCK1 pathway, which is involved in apoptosis and mitophagy, while Sal B significantly reduced ROCK1 protein levels. The protective effects of Sal B against oxLDL- and high Glu–induced endothelial dysfunction may be mediated by reductions in apoptosis-related proteins and fission proteins through suppression of the ROCK1-mediated pathway.

Galectin-3 aggravates ox-LDL-induced endothelial dysfunction through LOX-1 mediated signaling pathway.

Galectin-3, a biomarker linking oxidative stress and inflammation, participates in different mechanisms related to atherothrombosis, such as inflammation, proliferation, or macrophage chemotaxis. Accumulating evidence indicates that galectin-3 may also promote atherogenesis through inducing endothelial dysfunction. Lectin-like oxidized low-density lipoprotein (oxLDL) receptor-1 (LOX-1), a receptor for oxLDL uptake, contributes to oxLDL-induced endothelial dysfunction. Whether galectin-3 induces endothelial dysfunction through modulation of LOX-1-mediated signaling remains unclear. In the present study, we explored the mechanisms underlying galectin-3 enhanced cytotoxicity of oxLDL in human umbilical vein endothelial cells (HUVECs) and the role of LOX-1. Incubation of HUVECs with galectin-3 increased the expression of LOX-1 in RNA and protein levels. In addition, the expression of LOX-1 induced by oxLDL was promoted by galectin-3. However, pretreatment of LOX-1 antibody reduced LOX-1 mRNA expression level in cells with oxLDL plus galectin-3 incubation. Compared to cells treated with oxLDL alone, reactive oxygen species (ROS) generation via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and subsequent activation of p38 mitogen-activated protein kinases followed by nuclear factor kappa B (NF-κB) activation and related inflammatory responses including adhesion molecule expression, adhesiveness of monocytic cells, and IL-8 release were also aggravated in cells treated with galectin-3 combined with oxLDL. Compared to cells treated with galectin-3 plus oxLDL group. We found that LOX-1 antibody mitigated NADPH oxidase activity, p-38 up-regulation, NF-κB activation, and proinflammatory responses in cells treated with galectin-3 combined with oxLDL. We conclude that galectin-3 enhances endothelial LOX-1 expression and propose a new mechanism by which galectin-3 may promote endothelial dysfunction by inducing inflammation via LOX-1/ROS/p38/NF-κB-mediated signaling pathway.

Indicaxanthin from Opuntia ficus indica (L. Mill) Inhibits Oxidized LDL-Mediated Human Endothelial Cell Dysfunction through Inhibition of NF-κB Activation.

Oxidized low-density lipoproteins (oxLDL) play a pivotal role in the etiopathogenesis of atherosclerosis through the activation of inflammatory signaling events eventually leading to endothelial dysfunction and senescence. In the present work, we investigated the effects of indicaxanthin, a bioavailable, redox-modulating phytochemical from Opuntia ficus indica fruits, with anti-inflammatory activity, against oxLDL-induced endothelial dysfunction. Human umbilical vein cord cells (HUVEC) were stimulated with human oxLDL, and the effects of indicaxanthin were evaluated in a range between 5 and 20 μM, consistent with its plasma level after a fruit meal (7 μM). Pretreatment with indicaxanthin significantly and concentration-dependently inhibited oxLDL-induced cytotoxicity; ICAM-1, VCAM-1, and ELAM-1 increase; and ABC-A1 decrease of both protein and mRNA levels. From a mechanistic perspective, we also provided evidence that the protective effects of indicaxanthin were redox-dependent and related to the pigment efficacy to inhibit NF-κB transcriptional activity. In conclusion, here we demonstrate indicaxanthin as a novel, dietary phytochemical, able to exert significant protective vascular effects in vitro, at nutritionally relevant concentrations.

ENOS S-nitrosylation mediated OxLDL-induced endothelial dysfunction via increasing the interaction of eNOS with β‑catenin

Protein S-nitrosylation plays an important role in the progression of cardiovascular diseases. eNOS can be S-nitrosylated in endothelial cells, and this modification reversibly attenuates enzyme activity. Under physiological conditions, eNOS directly interacts with β‑catenin. However, whether and how eNOS S-nitrosylation regulates the β‑catenin signal pathway and participates in endothelial dysfunction remains unknown. Here, we show that OxLDL induces the S-nitrosylation of eNOS, which enhances the interaction between eNOS and β‑catenin, transcriptional activity of β‑catenin, cell migration and adhesion molecule expression in endothelial cells. In addition, these effects are partially abolished after eNOS is mutated at Cys94 and Cys99, but not Cys441, in endothelial cells. Furthermore, OxLDL increases iNOS expression. The specific iNOS inhibitor 1400 W decreases eNOS S-nitrosylation and the association of eNOS and β‑catenin, thereby blocking the β‑catenin signal pathway to alleviate OxLDL-induced endothelial dysfunction. Taken together, OxLDL induces eNOS S-nitrosylation at Cys94 and Cys99 via an iNOS-dependent manner, which may increase β‑catenin activation and trigger endothelial injury. This study describes a novel mechanism of endothelial dysfunction.

Pinoresinol Diglucoside Alleviates oxLDL-Induced Dysfunction in Human Umbilical Vein Endothelial Cells.

Atherosclerotic cardiovascular diseases are the leading causes of morbidity and mortality worldwide. Deposition of oxidized low-density lipoprotein (oxLDL) is one of the initiators and promoters of atherosclerosis. Eucommia lignans were shown to possess antihypertensive effects. This study aimed to investigate the effects of pinoresinol diglucoside (PD), a Eucommia lignan, on oxLDL-induced endothelial dysfunction. HUVECs were treated with oxLDL and/or PD followed by assessing radical oxygen species (ROS), apoptosis, nitrogen oxide (NO), malondialdehyde (MDA), and superoxide dismutase (SOD) activity with specific assays kits, mRNA levels with quantitative real-time polymerase chain reaction (PCR), and protein levels with western blot. PD abolished oxLDL-induced ROS and MDA production, apoptosis, upregulation of lectin-like oxidized LDL recptor-1 (LOX-1), intercellular Adhesion Molecule 1 (ICAM-1), and nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB), and activation of p38MAPK (mitogen-activated protein kinases)/NF-κB signaling. Meanwhile, PD alleviated oxLDL-caused inhibition of SOD activity, eNOS expression, and NO production. These data demonstrated that PD was effective in protecting endothelial cells from oxLDL-caused injuries, which guarantees further investigation on the clinical benefits of PD on cardiovascular diseases.

Idebenone protects against oxidized low density lipoprotein induced mitochondrial dysfunction in vascular endothelial cells via GSK3β/β-catenin signalling pathways

The early stages of the atherosclerotic process are initiated by accumulation of oxidized low-density lipoprotein (oxLDL) and damage to the structure or function of the endothelium. Antioxidant supplementation may be a plausible strategy to prevent atherosclerotic disease by quenching excessive reactive oxidative species. In the present study, we demonstrated that idebenone at suitable concentrations significantly prevented oxLDL-induced endothelial dysfunction. The underlying mechanisms of idebenone included inhibition of oxidative damage, suppression of the down-regulation of Bcl-2 and up-regulation of Bax and cleaved caspase-3 in human umbilical vein endothelial cells (HUVECs) exposed to oxLDL. Moreover, idebenone pretreatment inhibited oxLDL-mediated HUVECs damage by attenuating lipid peroxidation and promoting SOD activity. Finally, pro-incubation with idebenone inhibited mitochondrial dysfunction induced by oxLDL through the mitochondrial-dependent apoptotic pathway and GSK3β/β-catenin signalling pathways. In summary, idebenone is a promising agent in the treatment or prevention of atherosclerosis via inhibiting oxidative stress and improving mitochondrial function.

Abstract 575: NEDDylation Promotes Endothelial Dysfunction: A Role for HDAC2

Emerging evidence strongly supports a role for HDAC2 in the transcriptional regulation of endothelial genes and vascular function. We have recently demonstrated that HDAC2 reciprocally regulates the transcription of Arginase2, which is itself a critical modulator of endothelial function via eNOS. Moreover HDAC2 levels are decreased in response to the atherogenic stimulus OxLDL via a mechanism that is apparently dependent upon proteasomal degradation. NEDDylation is a post-translational protein modification that is tightly linked to ubiquitination and thereby protein degradation. We propose that changes in NEDDylation may modulate vascular endothelial function in part through alterations in the proteasomal degradation of HDAC2. In HAEC, OxLDL exposure augmented global protein NEDDylation. Pre-incubation of mouse aortic rings with the NEDDylation activating enzyme inhibitor, MLN4924, prevented OxLDL-induced endothelial dysfunction. In HAEC, MLN enhanced HDAC2 abundance, decreased expression and activity of Arg2, and blocked OxLDL-mediated reduction of HDAC2. Additionally, HDAC2 was shown to be a substrate for NEDD8 conjugation and this interaction was potentiated by OxLDL. Further, HDAC2 levels were reciprocally regulated by ectopic expression of NEDD8 and the de-NEDDylating enzyme SENP8. Our findings indicate that the observed improvement in endothelial dysfunction with inhibition of NEDDylation activating enzyme is likely due to an HDAC2-dependent decrease in Arginase2. NEDDylation activating enzyme may therefore be a novel target in endothelial dysfunction and atherogenesis.

NEDDylation promotes endothelial dysfunction: A role for HDAC2

Emerging evidence strongly supports a role for HDAC2 in the transcriptional regulation of endothelial genes and vascular function. We have recently demonstrated that HDAC2 reciprocally regulates the transcription of Arginase2, which is itself a critical modulator of endothelial function via eNOS. Moreover HDAC2 levels are decreased in response to the atherogenic stimulus OxLDL via a mechanism that is apparently dependent upon proteasomal degradation. NEDDylation is a post-translational protein modification that is tightly linked to ubiquitination and thereby protein degradation. We propose that changes in NEDDylation may modulate vascular endothelial function in part through alterations in the proteasomal degradation of HDAC2. In HAEC, OxLDL exposure augmented global protein NEDDylation. Pre-incubation of mouse aortic rings with the NEDDylation activating enzyme inhibitor, MLN4924, prevented OxLDL-induced endothelial dysfunction. In HAEC, MLN enhanced HDAC2 abundance, decreased expression and activity of Arginase2, and blocked OxLDL-mediated reduction of HDAC2. Additionally, HDAC2 was shown to be a substrate for NEDD8 conjugation and this interaction was potentiated by OxLDL. Further, HDAC2 levels were reciprocally regulated by ectopic expression of NEDD8 and the de-NEDDylating enzyme SENP8. Our findings indicate that the observed improvement in endothelial dysfunction with inhibition of NEDDylation activating enzyme is likely due to an HDAC2-dependent decrease in Arginase2. NEDDylation activating enzyme may therefore be a novel target in endothelial dysfunction and atherogenesis.

OxLDL induces endothelial dysfunction and death via TRAF3IP2: Inhibition by HDL3 and AMPK activators

Oxidized low-density lipoprotein (oxLDL) induces endothelial cell death through the activation of NF-κB and AP-1 pathways. TRAF3IP2 is a redox-sensitive cytoplasmic adapter protein and an upstream regulator of IKK/NF-κB and JNK/AP-1. Here we show that oxLDL-induced death in human primary coronary artery endothelial cells (ECs) was markedly attenuated by the knockdown of TRAF3IP2 or the lectin-like oxLDL receptor 1 (LOX-1). Further, oxLDL induced Nox2/superoxide-dependent TRAF3IP2 expression, IKK/p65 and JNK/c-Jun activation, and LOX-1 upregulation, suggesting a reinforcing mechanism. Similarly, the lysolipids present in oxLDL (16:0-LPC and 18:0-LPC) and minimally modified LDL also upregulated TRAF3IP2 expression. Notably, whereas native HDL3 reversed oxLDL-induced TRAF3IP2 expression and cell death, 15-lipoxygenase-modified HDL3 potentiated its proapoptotic effects. The activators of the AMPK/Akt pathway, adiponectin, AICAR, and metformin, attenuated superoxide generation, TRAF3IP2 expression, and oxLDL/TRAF3IP2-mediated EC death. Further, both HDL3 and adiponectin reversed oxLDL/TRAF3IP2-dependent monocyte adhesion to endothelial cells in vitro. Importantly, TRAF3IP2 gene deletion and the AMPK activators reversed oxLDL-induced impaired vasorelaxation ex vivo. These results indicate that oxLDL-induced endothelial cell death and dysfunction are mediated via TRAF3IP2 and that native HDL3 and the AMPK activators inhibit this response. Targeting TRAF3IP2 could potentially inhibit progression of atherosclerotic vascular diseases.

Tetrahydroxystilbene Glucoside Protects Against Oxidized LDL-Induced Endothelial Dysfunction via Regulating Vimentin Cytoskeleton and its Colocalization with ICAM-1 and VCAM-1

Background: Endothelial cell dysfunction triggered by oxidized low-density lipoprotein (oxLDL) is the main event occurring during the development of atherosclerosis. 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (TSG), an active component of the rhizome extract from Polygonum multiflorum, exhibits significant anti-atherosclerotic activity. However, the protective effects of TSG against oxLDL-induced endothelial dysfunction have not been clarified. We investigated the cytoprotective effects of TSG in human umbilical vein endothelial cells (HUVECs) and explored underlying mechanisms. Methods and Results: TSG pretreatment markedly attenuated oxLDL-mediated loss of cell viability, release of lactate dehydrogenase (LDH), cell apoptosis, and monocyte adhesion. OxLDL increased vimentin mRNA and protein levels, vimentin cleavage, caspase-3 activation, adhesion molecules levels and their colocalization with vimentin in HUVECs. These alterations were attenuated by pretreatment with TSG. Meanwhile, TSG inhibited both the expression of TGFβ1 and the phosphorylation of Smad2 and Smad3, and TSG suppressed the nuclear translocation of Smad4 induced by oxLDL. Using shRNA, oxLDL-induced cell apoptosis and monocyte adhesion were significantly inhibited by vimentin suppression in HUVECs. Conclusions: These results suggest that TSG protects HUVECs against oxLDL-induced endothelial dysfunction through inhibiting vimentin expression and cleavage, and the expression of adhesion molecules and their colocalization with vimentin. The interruption of TGFβ/Smad pathway and caspase-3 activation appears to be responsible for the downregulation of TSG on vimentin expression and fragmentation, respectively.

Isothiocyanates protect against oxidized LDL-induced endothelial dysfunction by upregulating Nrf2-dependent antioxidation and suppressing NFκB activation

Oxidative stress plays a pivotal role in the pathophysiology of cardiovascular diseases. Oxidized low-density lipoprotein (oxLDL) is a key contributor to atherogenesis through multiple mechanisms. In this study, we investigated the protection by three structurally related isothiocyanates, i.e., sulforaphane (SFN), benzyl isothiocyanate (BITC), and phenethyl isocyanate (PEITC), against oxLDL-induced leukocyte adhesion to vascular endothelium and the mechanism involved. The protection against oxLDL-induced endothelial dysfunction by isothiocyanates was studied in human umbilical vein endothelial cells (HUVECs). oxLDL increased reactive oxygen species (ROS) production, stimulated nuclear factor-kappaB (NFκB) activation, and enhanced intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and E-selectin expression in HUVECs, which led to promotion of monocyte adhesion to HUVECs. Treatment with SFN, BITC, and PEITC (0-10 μM) dose-dependently induced heme oxygenase (HO)-1, glutamate cysteine ligase (GCL) catalytic and modifier subunit expression, intracellular glutathione content, and antioxidant response element (ARE)-luciferase reporter activity. SFN, BITC, and PEITC pretreatment reversed oxLDL-induced ROS production, NFκB nuclear translocation, κB-reporter activity, ICAM-1, VCAM-1, and E-selectin expression, and monocyte adhesion to endothelial cells. Both heme oxygenase 1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) knockdown attenuated the isothiocyanate inhibition of oxLDL-induced ROS production, κB-reporter activity, and adhesion molecule expression. SFN, BITC, and PEITC protect against oxLDL-induced endothelial damage by upregulating Nrf2-dependent HO-1 and GCL expression, which leads to inhibition of NFκB activation and ICAM-1, VCAM-1, and E-selectin expression.

Ginkgo biloba extract attenuates oxLDL-induced endothelial dysfunction via an AMPK-dependent mechanism

Atherosclerosis is a complex inflammatory arterial disease, and oxidized low-density lipoprotein (oxLDL) is directly associated with chronic vascular inflammation. Previous studies have shown that Ginkgo biloba extract (GbE) acts as a therapeutic agent for neurological and cardiovascular disorders. However, the mechanisms mediating the actions of GbE are still largely unknown. In the present study, we tested the hypothesis that GbE protects against oxLDL-induced endothelial dysfunction via an AMP-activated protein kinase (AMPK)-dependent mechanism. Human umbilical vein endothelial cells were treated with GbE, followed by oxLDL, for indicated time periods. Results from Western blot showed that GbE inhibited the membrane translocation of the NADPH oxidase subunits p47(phox) and Rac-1 and attenuated the increase in protein expression of membrane subunits gp91 and p22(phox) caused by oxLDL-induced AMPK dephosphorylation and subsequent PKC activation. AMPK-α(1)-specific small interfering RNA-transfected cells that had been exposed to GbE followed by oxLDL revealed elevated levels of PKC and p47(phox). In addition, exposure to oxLDL resulted in reduced AMPK-mediated Akt/endothelial nitric oxide (NO) synthase signaling and the induction of phosphorylation of p38 mitogen-activated protein kinase, which, in turn, activated NF-κB-mediated inflammatory responses, such as the release of interleukin-8, the expression of the adhesion molecule, and the adherence of monocytic cells to human umbilical vein endothelial cells. Furthermore, oxLDL upregulated the expression of inducible NO synthase, thereby augmenting the formation of NO and protein nitrosylation. Pretreatment with GbE, however, exerted significant cytoprotective effects in a dose-dependent manner. Results from this study may provide insight into a possible molecular mechanism by which GbE protects against oxLDL-induced endothelial dysfunction.

Ellagic acid inhibits oxidized LDL-mediated LOX-1 expression, ROS generation, and inflammation in human endothelial cells

LOX-1, a lectin-like receptor on endothelial cells, facilitates the uptake of oxidized low-density lipoprotein (oxLDL). Expression of LOX-1 is involved in the pathobiological effects of oxLDL in endothelial cells, including reactive oxygen species (ROS) generation, suppression of endothelial nitric oxide synthase (eNOS) activity, and leukocytic adhesion. Moderate consumption of phenolic-enriched food may have a protective effect against the development of atherosclerosis via the antioxidant capacity of phenolic compounds at the endothelial level. In this study, we determined whether ellagic acid, a polyphenolic compound widely distributed in fruits and nuts, protects against oxLDL-induced endothelial dysfunction by modulating the LOX-1-mediated signaling pathway. Human umbilical vein endothelial cells (HUVECs) were pretreated with ellagic acid at doses of 5, 10, 15, and 20 μM for 2 hours and then incubated with oxLDL (150 μg/mL) for an additional 24 hours. LOX-1 protein expression was markedly lower after exposure to oxLDL in HUVECs pretreated with ellagic acid or diphenyleneiodonium, a well-known inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, than in HUVECs exposed to oxLDL alone, suggesting that ellagic acid deactivates NADPH oxidase. We also found that oxLDL activated the membrane assembly of p47phox, Rac1, gp91 and p22phox, and the subsequent induction of ROS generation; however, ROS generation was markedly suppressed in cells pretreated with ellagic acid or anti-LOX-1 monoclonal antibody. In addition, oxLDL down-regulated eNOS and up-regulated inducible NO synthase (iNOS), thereby augmenting the formation of NO and protein nitrosylation. Furthermore, oxLDL induced the phosphorylation of p38 mitogen-activated protein kinase, activated the NF-κB-mediated inflammatory signaling molecules interleukin-(IL) 6 and IL-8 and the adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin, and stimulated the adherence of THP-1 (a human acute monocytic leukemia cell line) to HUVECs. Pretreatment with ellagic acid, however, exerted significant cytoprotective effects in all events. Findings from this study may provide insight into a possible molecular mechanism by which ellagic acid inhibits LOX-1-induced endothelial dysfunction. Our data indicate that ellagic acid exerts its protective effects by inhibiting NADPH oxidase-induced overproduction of superoxide, suppressing the release of NO by down-regulating iNOS, enhancing cellular antioxidant defenses, and attenuating oxLDL-induced LOX-1 up-regulation and eNOS down-regulation.

Crude extracts of Solanum lyratum protect endothelial cells against oxidized low-density lipoprotein-induced injury by direct antioxidant action

Oxidized low-density lipoprotein (oxLDL) is a proatherogenic molecule that accumulates in the vascular wall and contributes to the pathogenesis of vascular dysfunction early in the development of atherosclerosis. The whole plant of Solanum lyratum is a traditional Chinese medicine that has been used for centuries to treat cancer, tumors, and herpes. However, the cellular and molecular mechanisms of its antioxidant effects are still largely unknown. This study tested the hypothesis that Solanum lyratum Thunberg extract (SLE) could block oxLDL-induced endothelial dysfunction in cultured human umbilical vein endothelial cells (HUVECs). Possible mechanisms were explored. Antioxidative activities of SLE were assayed by measuring the scavenging of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) free radical and the inhibition of copper-mediated or cell-mediated LDL oxidation. Production of reactive oxygen species (ROS) and the expression of adhesion molecules were evaluated in HUVECs after exposure to oxLDL and treatment with SLE. Several apoptotic signaling pathways were investigated. SLE scavenged DPPH and also delayed the kinetics of LDL oxidation in a dose-dependent manner. SLE attenuated the level of oxLDL-induced ROS generation, diminished the expression of endothelial NO synthase (eNOS), and enhanced the expression of adhesion molecules (vascular cellular adhesion molecule-1, E-selectin, and monocyte chemotactic protein-1) and the adherence of monocytic THP-1 cells to HUVECs. OxLDL increased the concentration of intracellular calcium, disturbed the balance of the Bcl-2 protein family, destabilized the mitochondrial membrane potential, increased the amount of cytochrome c released into the cytosol, and increased the activation of caspase 3. These detrimental effects were ameliorated dose-dependently by SLE (P < .05). Crude extracts of Solanum lyratum protect against oxLDL-induced injury in endothelial cells by direct antioxidant action. Atherosclerosis is a chronic inflammatory disease characterized by lipid-laden lesions within arterialblood vessel walls. Inhibiting the oxidation of low-density lipoprotein may be an effective way to prevent or delay theprogression of atherosclerosis. This study underscores the potential clinical benefits and application of Solanum lyratumextract in controlling oxidized low-density lipoprotein-associated vascular injury and cardiovascular disease.

Roads to Dysfunction

See related article, pages 951–960 Oxidized low-density lipoprotein (oxLDL) is considered to be the strongest proatherogenic lipoprotein. OxLDL is rapidly taken up by endothelial cells and macrophages and via the steps of foam cell formation and cell death, oxLDL eventually accumulates in the lipid core of atherosclerotic plaques.1 The interaction of oxLDL with cells is mediated by several receptors.2 Members of the scavenger receptor family predominate in macrophages,3 whereas endothelial cells mainly take up oxLDL by the lectin-like ox-LDL receptor-1 (LOX-1).4 On binding to LOX-1, oxLDL activates a multitude of signaling cascades involving MAP kinases,5,6 protein kinase C (PKC),7,8 and protein kinase B9 in endothelial cells. The consequence of this cellular activation, is apoptosis and superoxide anion production, the latter originating from the NADPH oxidase and uncoupling of the endothelial NO synthase (eNOS). OxLDL therefore is a strong inducer of endothelial dysfunction, a state in which the endothelium, instead of generating NO, produces superoxide anions. OxLDL also modulates the specific activity of NOS. It increases caveolin I expression and the interaction of NOS with this protein impairs NO production.10 Furthermore, oxLDL modulates PKC activity and expression and this family of kinases has been shown to acutely attenuate eNOS-dependent NO production and to promote eNOS uncoupling during prolonged exposure times.11 Several observations suggest that the supply of eNOS with the substrate l-arginine is impaired in the presence of oxLDL: In hypercholesterolemia, supplementation of l-arginine improves endothelium-dependent relaxation and NO production;12,13 l-arginine also attenuates the development of atherosclerosis,14 and normalizes leukocyte adhesion …

C-reactive protein enhances LOX-1 expression in human aortic endothelial cells: relevance of LOX-1 to C-reactive protein-induced endothelial dysfunction.

C-reactive protein (CRP), a characteristic inflammatory marker, is a powerful predictor of cardiovascular events. Recent data suggest that CRP may also promote atherogenesis through inducing endothelial dysfunction. Lectin-like oxidized low-density lipoprotein (oxLDL) receptor-1 (LOX-1) is a newly identified endothelial receptor for oxLDL that plays a pivotal role in oxLDL-induced endothelial dysfunction. Whether CRP may regulate endothelial LOX-1 and induce endothelial dysfunction through this receptor is unknown. In the present study, we studied the in vitro effect of CRP on LOX-1 expression in human aortic endothelial cells (HAECs) and the role of LOX-1 in CRP-induced human monocyte adhesion to endothelium and oxLDL uptake by endothelial cells. Incubation of HAECs with CRP enhanced, in a dose- and time-dependent manner, LOX-1 mRNA and protein levels. Induction of LOX-1 protein was already present at 5 microg/mL CRP and reached a maximum at 25 microg/mL. This effect was reduced by antibodies against CD32/CD64, endothelin-1 (ET-1) and interleukin-6 (IL-6). The extent of stimulation of LOX-1 achieved by CRP was comparable to that elicited by high glucose and IL-6 and remained unchanged in presence of these factors. Finally, CRP increased, through LOX-1, both human monocyte adhesion to endothelial cells and oxLDL uptake by these cells. We conclude that CRP enhances endothelial LOX-1 expression and propose a new mechanism by which CRP may promote endothelial dysfunction, that of inducing LOX-1.

Phytoestrogen α-Zearalanol Antagonizes Oxidized LDL-Induced Inhibition of Nitric Oxide Production and Stimulation of Endothelin-1 Release in Human Umbilical Vein Endothelial Cells

Oxidative modification of low-density lipoprotein (LDL) leads to formation of the atherogenic molecule oxidized LDL (oxLDL), which is considered to be an important mediator for vascular endothelial dysfunction and atherosclerosis. It is speculated that reduced nitric oxide (NO) release/bioavailability and enhanced release of endothelin-1 (ET-1) may contribute to oxLDL-induced endothelial dysfunction. Estrogen may improve lipid profile and inhibit oxLDL-induced endothelial damage. However, estrogen replacement therapy has been suspended due to uncertainty in benefits versus risk (such as cancer progression) in postmenopausal women. This study was designed to evaluate the effect of a novel phytoestrogen, alpha-zearalanol (alpha-ZAL), on oxLDL-induced effect on NO and ET-1 production in human umbilical vein endothelial cells (HUVEC). HUVEC were incubated with oxLDL (50 microg/mL) for 24 h in the absence or presence of alpha-ZAL (0-1000 nM), 17beta-estradiol (E2, 10 nM), or the E2 receptor antagonist ICI182780 (1 microM). Levels of NO and ET-1 were measured by spectrophotometry and enzymatic immunoassay, respectively. NOS activity was evaluated by conversion of 3H-arginine to 3H-citrulline. Protein and mRNA expression of NOS and ET-1 were measured by Western blot and RT-PCR. Our results indicated that oxLDL significantly reduced NO release and NOS activity, and enhanced ET-1 pro-duction associated with reduced NOS3 (but not NOS2) expression and enhanced ET-1 mRNA expression. All these oxLDL-induced alterations were significantly attenuated or abolished by co-incubation with alpha-ZAL or E2, both through an E2 receptor-dependent mechanism. alpha-ZAL, E2, and ICI182780 had no effect on NO/ET-1 release, NOS activity, or expression of NOS and ET-1. These data suggested that the phytoestrogen alpha-ZAL, like E2, may effectively antagonize oxLDL-induced decrease in NO and increase in ET-1, which may be protective for endothelial function.