Associations of atherosclerotic risk factors with oxidized low-density lipoprotein evaluated by LOX-1 ligand activity in healthy men

Inhibition of circ_0000231 suppresses oxidized low density lipoprotein-induced apoptosis, autophagy and inflammation in human umbilical vein endothelial cells by regulating miR-590-5p/PDCD4 axis

BACKGROUND

Circular RNAs (circRNAs) are the emerging informative RNAs, involved in cardiovascular diseases including atherosclerosis (AS). Endothelial injury is the initial qualitative change of AS. Thus, the objective of this study was to confirm the dysregulation and mechanism of circ_0000231 in cell model of AS at early stage in human umbilical vein endothelial cells (HUVECs) induced by oxidized low-density lipoprotein (ox-LDL).

METHODS

The expression of circ_0000231, miR-590-5p and programmed cell death 4 (PDCD4) was detected using real-time quantitative PCR and western blot. Cell injury was measured with MTT, flow cytometry, caspase-3 activity assay and enzyme-linked immunosorbent assay (ELISA). The interaction among circ_0000231, miR-590-5p and PDCD4 was validated by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) and pull-down assays.

RESULTS

Stress ox-LDL decreased cell viability, and increased apoptosis rate and caspase-3 activity in HUVECs in a dose- and time-dependent manner in concomitant with promotions of interleukin-6, interleukin-1β, tumor necrosis factor-α, LC3-II/I and Beclin-1 levels. Besides, circ_0000231 and PDCD4 expressions were upregulated, and miR-590-5p was downregulated in ox-LDL-stimulated HUVECs. Functionally, knockdown of circ_0000231 and overexpression of miR-590-5p could suppress ox-LDL-elicited above effects on apoptosis, autophagy and inflammatory response, accompanied with PDCD4 downregulation. Physically, miR-590-5p could directly interact with circ_0000231 and PDCD4.

CONCLUSION

Downregulation of circ_0000231 suppresses HUVECs from ox-LDL-induced injury partially through regulating miR-590-5p/PDCD4 axis via competing endogenous RNA mechanism, showing a novel potential target for the pathology and treatment of endothelial injury in AS.

Endothelin-1 and LOX-1 as Markers of Endothelial Dysfunction in Obstructive Sleep Apnea Patients

INTRODUCTION

The search of biochemical markers of endothelial dysfunction: lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1)-involved in atherosclerotic plaques formation-and endothelin-1 (ET-1)-potent vasoconstrictor-might help in detecting obstructive sleep apnea (OSA) patients at high risk of cardiovascular diseases.

MATERIAL AND METHODS

In 71 OSA patients (apnoea/hypopnoea index, AHI 28.2 ± 17.9/hour) and in 21 healthy controls the serum levels of LOX-1 and ET-1 were measured.

RESULTS

There were increased levels of ET-1 (1.58 ± 0.65 vs. 1.09 ± 0.38 pg/mL; p < 0.001) but not of LOX-1 in OSA patients as compared with healthy controls. In the patients' group ET-1 levels negatively correlated with serum LDL levels. LOX-1 levels positively correlated with fasting glucose levels and were higher in the patients with than without diabetes. Neither ET-1 nor LOX-1 correlated with OSA severity. In mild OSA patients, there was a negative correlation between LOX-1 and mean arterial oxygen saturation during sleep. In severe OSA patients, there was a positive correlation between LOX-1 levels and uric acid.

CONCLUSION

There is endothelial dysfunction in OSA patients as indicated by increased serum levels of ET-1 and possibly endothelial dysfunction in diabetic OSA patients as indicated by increased serum levels of LOX-1 and its correlation with fasting glucose levels.

Association of circulating soluble lectin-like oxidized low-density lipoprotein receptor-1 with inflammatory markers and urinary albumin excretion in patients with type 2 diabetes

OBJECTIVES

The main purpose of the study was to study the association between circulating soluble lectin-like oxidized low-density lipoprotein receptor-1 levels and various markers, including inflammatory markers such as high-sensitivity C-reactive protein and fibrinogen, serum lipids, and renal function, in patients with poorly controlled type 2 diabetes.

METHODS

The subjects were 70 patients (men 45, women 25) who were hospitalized for treatment of poor glycemic control. Plasma soluble lectin-like oxidized low-density lipoprotein receptor-1 levels were assayed using a sandwich chemiluminescence enzyme immunoassay.

RESULTS

Circulating soluble lectin-like oxidized low-density lipoprotein receptor-1 was significantly positively correlated with lectin-like oxidized low-density lipoprotein-1 ligands containing apolipoprotein B, reflecting modified low-density lipoprotein, and with inflammatory markers such as high-sensitivity C-reactive protein and fibrinogen. In addition, there was a significant positive correlation between soluble lectin-like oxidized low-density lipoprotein receptor-1 and urinary albumin excretion.

CONCLUSIONS

Soluble lectin-like oxidized low-density lipoprotein receptor-1 may serve as a marker reflecting the degrees of inflammation and albuminuria in patients with poorly controlled type 2 diabetes.

"Benifuuki" Extract Reduces Serum Levels of Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1 Ligands Containing Apolipoprotein B: A Double-Blind Placebo-Controlled Randomized Trial

(1) Background: Arteriosclerosis is associated with high levels of low-density lipoprotein (LDL) cholesterol. O-methylated catechins in “Benifuuki” green tea are expected to reduce cholesterol levels, although there is limited research regarding this topic; (2) Methods: This trial evaluated 159 healthy volunteers who were randomized to receive ice cream containing a high-dose of “Benifuuki” extract including 676 mg of catechins (group H), a low-dose of “Benifuuki” extract including 322 mg of catechins (group L), or no “Benifuuki” extract (group C). Each group consumed ice cream (with or without extract) daily for 12 weeks, and their lipid-related parameters were compared; (3) Results: A significant reduction in the level of lectin-like oxidized LDL receptor-1 ligand containing ApoB (LAB) was detected in group H, compared to groups L and C. No significant differences between the three groups were detected in their levels of total cholesterol, triglycerides, and LDL cholesterol; (4) Conclusions: “Benifuuki” extract containing O-methylated catechins may help prevent arteriosclerosis.

Smoking cessation reduces the lectin-like low-density lipoprotein receptor index, an independent cardiovascular risk marker of vascular inflammation

Vessel wall inflammation promotes the destabilization of atherosclerotic plaques. The lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (LOX-1) expressed by vascular cells and monocytes. LOX index is calculated by multiplying LOX-1 ligand containing apolipoprotein B level with the soluble LOX-1. A high LOX index reflects an increased risk for stroke and myocardial infarction. However, the change in LOX index after smoking cessation and the relationship between smoking-related variables and LOX index are unknown. Relation of the clinical parameters to the LOX index was examined on 180 subjects (135 males and 45 females) at the first visit to our outpatient clinic for smoking cessation. The impact of smoking cessation on the LOX index was also determined in the 94 subjects (62 males and 32 females) who successfully stopped smoking. Sex-adjusted regression analysis and multivariate analysis identified three independent determinants of the LOX index, namely, low-density lipoprotein-cholesterol (LDL-C; β = 0.311, p < 0.001), high-sensitivity C-reactive protein (β = 0.358, p < 0.001), and expired carbon monoxide concentration reflecting smoking heaviness (β = 0.264, p = 0.003). Body mass index (BMI) significantly increased 3 months after the onset of smoking cessation (p < 0.001). However, the LOX index significantly decreased (p < 0.001), regardless of the rate of increase in BMI post-cessation. The LOX index is closely associated with smoking heaviness as well as dyslipidemia and an inflammation marker. Smoking cessation may induce a decrease in this cardiovascular risk marker, independently of weight gain.

Attenuation of spontaneous thrombolytic activity measured by the global thrombosis test in male habitual smokers

Smoking is known as one of the major risk factors for atherothrombotic cardiovascular diseases. We investigated the susceptibility to thrombosis in habitual smokers by using the global thrombosis test (GTT), by which both clot formation and clot lysis activities can be evaluated simultaneously in native blood samples in vitro. Subjects were 139 men participating in a periodic health checkup examination, and an informed consent for the subjects was obtained as a document. Using GTT, occlusion time (OT: the time taken for clot formation in the blood sample) and lysis time (LT: the time taken for lysis of the clot that had been formed) were measured. LT was significantly (p = 0.029) longer in smokers [median with range, 1,794 (1,080-6,000) s (n = 76)] than in nonsmokers [median with range, 1,530 (792-3,800) s (n = 63)], while there was no significant difference in OT between smokers and nonsmokers. In smokers, LT was significantly correlated with daily cigarette consumption but not with Brinkman index. LT measured in nine smokers at 3 months after quitting their habitual smoking was significantly shorter than LT measured before the cessation of smoking. Since prolongation of LT implies existence of thrombogenic tendency, smokers are thought to be more susceptible to thrombosis due to decreased fibrinolytic activity, and no smoking for even a short term may be effective for improving fibrinolytic activity in smokers.

Elevation of circulating LOX-1 ligand levels in Zucker obese and diabetic rats

LOX-1 ligands containing apolipoprotein B (LAB) reflect ligand activity of LOX-1, which is a key molecule for initiation of atherosclerosis. The Zucker rat is a well-known model used for research on obesity and diabetes. Blood levels of LAB were compared among Zucker fatty (ZF), Zucker diabetic fatty (ZDF) and Zucker lean (ZL) rats. Log-transformed LAB was significantly higher in ZF and ZDF rats than in control ZL rats, while no significant difference was found in log-transformed LAB of ZF and ZDF rats. This study for the first time demonstrated that circulating LOX-1 ligands were elevated in obesity and diabetes model rats.

LOX-1 and ROS, inseparable factors in the process of endothelial damage

Lectin-like oxidized low-density lipoprotein (LOX-1) has been identified in endothelial cells as the main receptor of oxidized low-density lipoprotein (OxLDL). LOX-1 is upregulated in the presence of pathological conditions including atherosclerosis, hypertension, and diabetes because it acts as a mediator of "endothelial dysfunction". It promotes the generation of superoxide anion (O2(-)), the inhibition of nitric oxide (NO) production and the increment of endothelial adhesiveness to monocytes. Recently, it was reported that OxLDL, binding to LOX-1, determined a significant increase in the generation of reactive oxygen species (ROS), suggesting the involvement of signaling pathways such as mitogen-activated protein kinases (MAPKs). It is now generally accepted that ROS act indirectly on the modulation of LOX-1 expression because ROS oxidize native LDL. Moreover, LOX-1 activation per se may stimulate ROS generation. Accordingly, our findings showed that high levels of ROS can directly increase LOX-1 production in microvascular endothelial cells (HMEC-1). It has been reported that OxLDL, usually > 20 μg protein/ml, induced apoptosis in a variety of cell types. At low concentrations (< 5 μg protein/ml) OxLDL appears to be associated with cell proliferation and low levels of ROS-induced capillary tube formation in endothelial cells. Our data and those of the literature indicate the existence of a direct control of LOX-1 by ROS. Although ROS in large amounts clearly have detrimental effects on cell biology, small amounts of ROS could have a beneficial effect, suggesting its therapeutic potential for reducing ischemic tissue.

Docosahexaenoic acid decreases TNF-α-induced lectin-like oxidized low-density lipoprotein receptor-1 expression in THP-1 cells

Docosahexaenoic acid (DHA) prevents atherosclerosis and may decrease monocyte/macrophage activation by tumor necrosis factor (TNF)-α. Here, we sought to determine the protective effects of DHA against TNF-α-induced stimulation of lectin-like oxidized low-density lipoprotein (LDL) receptor-1 (LOX-1) expression, which is associated with atherosclerosis. Using reverse transcription polymerase chain reaction, we found that TNF-α induced the expression of LOX-1 (OLR1), NADPH oxidase 2 (Nox2), p47phox (NCF1), very late antigen-4 (ITGA4), and lymphocyte function-associated antigen (ITGAL) genes. Additionally, DHA attenuated TNF-α-induced acetylated (Ac)-LDL uptake and reactive oxygen species (ROS) production, as measured using fluorescently labeled LDL and H2DCFDA, respectively, and reduced the expression levels of these genes. Moreover, the PI3 kinase inhibitor LY294002 blocked these effects of DHA. These results indicated that DHA inhibited several events associated with redox regulation in a PI3K-dependent manner, thereby mediating the expression of LOX-1 in monocytes/macrophages.

Lectin-like oxidized low-density lipoprotein receptor 1 pathways

BACKGROUND

The role of lectin-like oxidized low-density lipoprotein receptor (LOX)-1 has been implicated in the pathogenesis of different diseases, including atherosclerosis, hypertension, obesity, diabetes mellitus and metabolic syndrome. To date, several studies aimed at partially investigating the mechanistic role of LOX-1 in these various pathologies. Still, so far, the precise signal transduction pathways involving LOX-1 have not yet been elucidated.

MATERIALS AND METHODS

The most recent data published by the authors as well as others concerning different pathways involving LOX-1 are collected to formulate the presented updated review.

RESULTS

One of the most prominent pathways highlighted in the present review is the relationship of LOX-1 to NADPH oxidase that acts as a major source of harmful free radicals causing oxidative stress in blood vessels. Other pathways involve lipid and glucose metabolism-mediated signal transduction.

DISCUSSION

The modulatory role of LOX-1 on nitric oxide and renin/angiotensin systems as well as on fibrosis, apoptosis and inflammatory pathways is discussed.

CONCLUSION

The current review revisits LOX-1 and its related pathways, implicating LOX-1 as a target for ameliorating various pathological conditions.

Cutaneous microvascular dysfunction correlates with serum LDL and sLOX-1 receptor concentrations

The human cutaneous circulation is an accessible and representative regional circulation for investigating mechanisms of microvascular dysfunction, a systemic disease process occurring early in the pathogenesis of atherosclerosis. Elevated concentrations of low-density lipoproteins ([LDL]) are highly atherogenic and independently associated with the severity of coronary atherosclerosis through their actions on the lectin-like oxidized LDL receptors (LOX-1). We hypothesized that cutaneous microvascular dysfunction, as measured by a decrement in endothelial nitric oxide- (NO-) dependent vasodilation during local heating, would be correlated with serum [LDL], oxidized [LDL], and soluble LOX-1 receptors [sLOX-1]. Intradermal microdialysis fibers were placed in the skin of 53 otherwise healthy men and women (aged 52±8 years) whose serum [LDL] ranged from 72 to 233 mg/dL. Skin blood flow was measured by laser Doppler flowmetry over a local forearm skin site as it was heated (42°C) to induce sustained local vasodilation. After flux plateaued, L-NAME was infused to block endothelial NO synthase in order to determine the NO-dependent portion of the vasodilatory response. Data were normalized to maximal cutaneous vascular conductance (CVC). NO-dependent vasodilation was reduced as a linear function of [LDL] (R(2)=0.303, p<0.001), oxidized [LDL] (R(2)=0.214, p<0.001), and [sLOX-1] (R(2)=0.259, p=0.026) but was unrelated to high-density lipoprotein (HDL) concentration (R(2)=0.003, p=0.68). Hypercholesterolemia-induced microvascular dysfunction is related to various LDL markers and involves a reduction in NO-dependent vasodilation that appears to be a progressive process measurable in the skin microcirculation.

LOX-1 in atherosclerosis: biological functions and pharmacological modifiers

Lectin-like oxidized LDL (oxLDL) receptor-1 (LOX-1, also known as OLR-1), is a class E scavenger receptor that mediates the uptake of oxLDL by vascular cells. LOX-1 is involved in endothelial dysfunction, monocyte adhesion, the proliferation, migration, and apoptosis of smooth muscle cells, foam cell formation, platelet activation, as well as plaque instability; all of these events are critical in the pathogenesis of atherosclerosis. These LOX-1-dependent biological processes contribute to plaque instability and the ultimate clinical sequelae of plaque rupture and life-threatening tissue ischemia. Administration of anti-LOX-1 antibodies inhibits atherosclerosis by decreasing these cellular events. Over the past decade, multiple drugs including naturally occurring antioxidants, statins, antiinflammatory agents, antihypertensive and antihyperglycemic drugs have been demonstrated to inhibit vascular LOX-1 expression and activity. Therefore, LOX-1 represents an attractive therapeutic target for the treatment of human atherosclerotic diseases. This review aims to integrate the current understanding of LOX-1 signaling, regulation of LOX-1 by vasculoprotective drugs, and the importance of LOX-1 in the pathogenesis of atherosclerosis.