Upregulation of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) in endothelial cells by nitric oxide deficiency

ADMA: A Key Player in the Relationship between Vascular Dysfunction and Inflammation in Atherosclerosis

Atherosclerosis is a chronic cardiovascular disease which increases risk of major cardiovascular events including myocardial infarction and stroke. Elevated plasma concentrations of asymmetric dimethylarginine (ADMA) have long been recognised as a hallmark of cardiovascular disease and are associated with cardiovascular risk factors including hypertension, obesity and hypertriglyceridemia. In this review, we discuss the clinical literature that link ADMA concentrations to increased risk of the development of atherosclerosis. The formation of atherosclerotic lesions relies on the interplay between vascular dysfunction, leading to endothelial activation and the accumulation of inflammatory cells, particularly macrophages, within the vessel wall. Here, we review the mechanisms through which elevated ADMA contributes to endothelial dysfunction, activation and reactive oxygen species (ROS) production; how ADMA may affect vascular smooth muscle phenotype; and finally whether ADMA plays a regulatory role in the inflammatory processes occurring within the vessel wall.

Soluble Lectin-Like Oxidized Low-Density Lipoprotein Receptor 1 Is Inversely Correlated with the Activity of ANCA-Associated Vasculitis

Lectin-like oxidized low-density lipoprotein (LDL) receptor 1 (LOX1) binds to oxidized LDL, which is associated with inflammation in various vascular disorders. Here, we aimed to investigate the potential of soluble LOX1 (sLOX1) as an indicator of antineutrophil cytoplasmic antibody-associated vasculitis (AAV) activity. Serum levels of sLOX1 in frozen samples from patients with AAV enrolled in a prospective observational cohort study at the Severance Hospital were measured using enzyme-linked immunosorbent assay. Clinical and laboratory data were collected on the date when the blood sampling was performed. The association between sLOX1 and clinical and laboratory data was assessed using Pearson's correlation analysis. The median age of the recruited 79 patients was 62.0 years, and 27 (34.2%) patients were men. The median Birmingham vasculitis activity score (BVAS), five-factor score, vasculitis damage index, and sLOX1 level were 6, 1, 3, and 911.9 pg/mL, respectively. Correlation analysis based on BVAS revealed that sLOX1 and total cholesterol were significantly inversely correlated with BVAS (r=-0.224, p=0.047 and r=-0.424, p<0.001, respectively). No significant correlations were observed between continuous variables and sLOX1 except for BVAS, although total cholesterol tended to correlate with sLOX1 (r=0.190, p=0.093). Additionally, sLOX1 was not influenced by sex, hypertension, diabetes mellitus, or the presence of pulmonary, cardiovascular, and renal involvement of AAV. In summary, sLOX1 was inversely correlated with BVAS in AAV patients, which is different from other vascular diseases or inflammatory diseases.

Role of the eNOS Uncoupling and the Nitric Oxide Metabolic Pathway in the Pathogenesis of Autoimmune Rheumatic Diseases

Atherosclerosis and its clinical complications constitute the major healthcare problems of the world population. Due to the central role of endothelium throughout the atherosclerotic disease process, endothelial dysfunction is regarded as a common mechanism for various cardiovascular (CV) disorders. It is well established that patients with rheumatic autoimmune diseases are characterized by significantly increased prevalence of cardiovascular morbidity and mortality compared with the general population. The current European guidelines on cardiovascular disease (CVD) prevention in clinical practice recommend to use a 1,5-factor multiplier for CV risk in rheumatoid arthritis as well as in other autoimmune inflammatory diseases. However, mechanisms of accelerated atherosclerosis in these diseases, especially in the absence of traditional risk factors, still remain unclear. Oxidative stress plays the major role in the endothelial dysfunction and recently is strongly attributed to endothelial NO synthase dysfunction (eNOS uncoupling). Converted to a superoxide-producing enzyme, uncoupled eNOS not only leads to reduction of the nitric oxide (NO) generation but also potentiates the preexisting oxidative stress, which contributes significantly to atherogenesis. However, to date, there are no systemic analyses on the role of eNOS uncoupling in the excess CV mortality linked with autoimmune rheumatic diseases. The current review paper addresses this issue.

Hydrogen sulfide potentiates the favorable metabolic effects of inorganic nitrite in type 2 diabetic rats

OBJECTIVE

Decreased nitric oxide (NO) bioavailability and hydrogen sulfide (H₂S) deficiency have been linked with the pathophysiology of type 2 diabetes (T2D). Restoration of NO levels by nitrite have been associated with favorable metabolic effects in T2D. Moreover, H₂S can potentiate the effects of NO in the cardiovascular system. The aim of this study was to determine the effects of long-term co-administration of sodium nitrite and sodium hydrosulfide (NaSH) on carbohydrate metabolism in type 2 diabetic rats.

METHODS

T2D was induced using chronic high fat diet (HFD) feeding combined with low dose streptozotocin (STZ) regimen. Rats were divided into 5 groups (N = 10/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite + NaSH. Nitrite (50 mg/L in drinking water) and NaSH (0.28 mg/kg, daily i. p. injection) were administered for 9 weeks. Fasting serum glucose, insulin, lipid profile, liver function tests, and oxidative stress indices were measured. Intraperitoneal glucose tolerance test (GTT) was performed at the end of the eighth week, and three days later, intraperitoneal pyruvate tolerance test (PTT) was done. Protein levels and mRNA expression of glucose transporter type 4 (GLUT4) in soleus muscle and epididymal adipose tissue as well as mRNA expression of H₂S-producing enzymes in the liver, soleus muscle, and epididymal adipose tissue were measured at the end of the study.

RESULTS

Compared to the controls, HFD and STZ treated rats developed metabolic dysfunction. Nitrite treatment improved carbohydrate metabolism, liver function, and oxidative stress indices whereas NaSH treatment per se had no significant effects. However, co-administration of NaSH and nitrite resulted in further improvement in serum insulin level, GTT, PTT, liver function, oxidative stress, protein level and mRNA expression of GLUT4, as well as mRNA expression of H₂S-producing enzymes in diabetic rats.

CONCLUSION

Low dose of NaSH per se had no effect on carbohydrate metabolism while it potentiated the favorable metabolic effects of inorganic nitrite in type 2 diabetic rats. These favorable effects were associated with decreased oxidative stress and increased GLUT4 expression in insulin-sensitive tissues as well as improvement of liver function.

Effects of long-term oral nitrate administration on adiposity in normal adult female rats

INTRODUCTION

Nitric oxide (NO) deficiency is associated with obesity. Nitrate could act as a substrate for production of NO and is a novel therapeutic agent in obesity. This study aims at determining effects of long-term nitrate administration on obesity indices in normal adult female rats.

METHODS

Female Wistar rats were divided into four groups (n = 10/each): i.e. control group received tap water and three treatment groups received water containing 50, 100 and 150 mg/L sodium nitrate for 6 months. Body weight (g) was measured monthly; naso-anal length (cm) and obesity indices including body mass index (BMI), Lee index, abdominal and thoracic circumferences were determined every two months. Both white adipose tissue (WAT) and brown adipose tissue (BAT) were weighted and then adiposity index was calculated. In addition, level of NOx (nitrate + nitrite) in serum and adipose tissues were measured at the end of the study.

RESULTS

Compared to controls, body weights and naso-anal length were significantly (P < 0.001) lower in all nitrate-treated rats. Compared to controls, nitrate-treated rats had also lower adiposity indices, BMI, Lee index, abdominal and thoracic circumferences (13%, 17% and 22% for BMI and 5%, 6% and 8% for lee index at dose 50, 100, and 150 mg/L, respectively). In addition, nitrate administration increased NOx levels in serum and adipose tissues.

CONCLUSIONS

Long-term nitrate administration has favorable effects on adiposity. It increases brown and decreases white adipose tissues in normal female rats; these observations could potentially help in management of obesity.

Role of Uremic Toxins for Kidney, Cardiovascular, and Bone Dysfunction

With decreasing kidney function, cardiovascular disease (CVD) and mineral bone disorders frequently emerge in patients with chronic kidney disease (CKD). For these patients, in addition to the traditional risk factors, non-traditional CKD-specific risk factors are also associated with such diseases and conditions. One of these non-traditional risk factors is the accumulation of uremic toxins (UTs). In addition, the accumulation of UTs further deteriorates kidney function. Recently, a huge number of UTs have been identified. Although many experimental and clinical studies have reported associations between UTs and the progression of CKD, CVD, and bone disease, these relationships are very complex and have not been fully elucidated. Among the UTs, indoxyl sulfate, asymmetric dimethylarginine, and p-cresylsulfate have been of particular focus, up until now. In this review, we summarize the pathophysiological influences of these UTs on the kidney, cardiovascular system, and bone, and discuss the clinical data regarding the harmful effects of these UTs on diseases and conditions.

Effects of long-term nitrate supplementation on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in male obese type 2 diabetic rats

PURPOSE

Supplementation with inorganic nitrate to boost the nitrate-nitrite-nitric oxide (NO) pathway, may act as a potential therapeutic agent in diabetes. The aim of this study was to determine the effects of nitrate on carbohydrate metabolism, lipid profiles, oxidative stress, and inflammation in obese type 2 diabetic rats.

METHODS

Male Wistar rats were divided into 4 groups: Control, control + nitrate, diabetes, and diabetes + nitrate. Diabetes was induced using a high-fat diet and low-dose of streptozotocin. Sodium nitrate (100 mg/L in drinking water) was administered simultaneously for two months. Serum levels of fasting glucose, insulin, and lipid profiles were measured every 2-weeks. Glycated hemoglobin (HbA1c) was measured monthly. Serum thiobarbituric reactive substances (TBARS) level and catalase activity were measured before and after treatment. At the end of the study, glucose, pyruvate, and insulin tolerance tests were done. Glucose-stimulated insulin secretion (GSIS) and insulin content from isolated pancreatic islets were also assessed; mRNA expression of iNOS as well as mRNA expression and protein levels of GLUT4 in insulin-sensitive tissues, and serum IL-1β were determined.

RESULTS

Nitrate supplementation in diabetic rats significantly improved glucose tolerance, lipid profiles, and catalase activity as well as decreased gluconeogenesis, fasting glucose, insulin, and IL-1β; although it had no significant effect on GSIS, islet insulin content, HbA1c, and serum TBARS. Compared to the controls, in diabetic rats, mRNA expression and protein levels of GLUT4 were significantly lower in the soleus muscle (54% and 34%, respectively) and epididymal adipose tissue (67% and 41%, respectively). In diabetic rats, nitrate administration increased GLUT4 mRNA expression and protein levels in both soleus muscle (215% and 17%, respectively) and epididymal adipose tissue (344% and 22%, respectively). In diabetic rats, nitrate significantly decreased elevated iNOS mRNA expression in both the soleus muscle and epididymal adipose tissue.

CONCLUSION

Chronic nitrate supplementation in obese type 2 diabetic rats improved glucose tolerance, insulin resistance, and dyslipidemia; these favorable effects were associated with increased mRNA and protein expression of GLUT4 and decreased mRNA expression of iNOS in insulin-sensitive tissues, and with decreased gluconeogenesis, inflammation, and oxidative stress.

Nitrite increases glucose-stimulated insulin secretion and islet insulin content in obese type 2 diabetic male rats

PURPOSE

Reduced bioavailability of nitric oxide (NO) is associated with pathogenesis of type 2 diabetes. Nitrite can act as a substrate for generation of systemic NO. The aim of this study was to examine the effects of nitrite administration on glucose-stimulated insulin secretion (GSIS) and islet insulin content in obese type 2 diabetic rats.

METHODS

Male rats were divided into 4 groups: Control, control + nitrite, diabetes, and diabetes + nitrite. Sodium nitrite (50 mg/L in drinking water) was administered for 8 weeks. Diabetes was induced using high-fat diet and low-dose of streptozotocine. Serum levels of fasting glucose, insulin, and lipid profile were measured and the insulin resistance/sensitivity indices were calculated every 2 weeks. Glycated hemoglobin (HbA_1C) was measured every month. At the end of the study, tissue levels of glucose transporter 4 (GLUT4) protein and serum interleukin-1 beta (IL-1β) were measured as well as glucose and insulin tolerance test were done. GSIS from isolated pancreatic islets and islet insulin content were also determined.

RESULTS

Nitrite administration significantly increased insulin secretion in both control and diabetic rats in presence of 16.7 mM glucose. Nitrite also significantly increased islet insulin content by 27% and 39% in both control and diabetic rats, respectively. Nitrite decreased elevated serum IL-1β in diabetic rats (4.0 ± 0.2 vs. 2.9 ± 0.2 pg/mL, P = 0.001). In diabetic rats, nitrite also significantly increased tissue levels of GLUT4 by 22% and 26% in soleus muscle and epididymal adipose tissue, respectively. In addition, nitrite significantly improved glucose and insulin tolerance, insulin sensitivity, lipid profile, and decreased fasting glucose and insulin, but had no effect on HbA_1C.

CONCLUSIONS

Long-term nitrite administration increased both insulin secretion and insulin content in obese type 2 diabetic rats. In addition, nitrite therapy had favorable effects on glucose tolerance, insulin resistance, inflammation, and dyslipidemia in type 2 diabetic rats.

Pathogenesis of endothelial cell dysfunction in chronic kidney disease: a retrospective and what the future may hold

Cardiovascular complications dominate the landscape of chronic kidney diseases (CKD). Endothelial cell dysfunction (ECD) is a well-known culprit of cardiovascular morbidity and it develops in CKD with remarkable frequency. This brief overview of ECD in CKD scans two decades of studies performed in my laboratory, from genetic analyses to proteomic and metabolomics screens. I provide a detailed description of findings related to the premature senescence of endothelial cells, cell transition from the endothelial to mesenchymal phenotype, and stages of development of ECD. Clinical utility of some of these findings is illustrated with data on laser-Doppler flowmetry and imaging in patients with CKD. Some currently available and emerging therapeutic options for the management of ECD are briefly presented.

Human serum amyloid A3 (SAA3) protein, expressed as a fusion protein with SAA2, binds the oxidized low density lipoprotein receptor

Serum amyloid A3 (SAA3) possesses characteristics distinct from the other serum amyloid A isoforms, SAA1, SAA2, and SAA4. High density lipoprotein contains the latter three isoforms, but not SAA3. The expression of mouse SAA3 (mSAA3) is known to be up-regulated extrahepatically in inflammatory responses, and acts as an endogenous ligand for the toll-like receptor 4/MD-2 complex. We previously reported that mSAA3 plays an important role in facilitating tumor metastasis by attracting circulating tumor cells and enhancing hyperpermeability in the lungs. On the other hand, human SAA3 (hSAA3) has long been regarded as a pseudogene, which is in contrast to the abundant expression levels of the other isoforms. Although the nucleotide sequence of hSAA3 is very similar to that of the other SAAs, a single oligonucleotide insertion in exon 2 causes a frame-shift to generate a unique amino acid sequence. In the present study, we identified that hSAA3 was transcribed in the hSAA2-SAA3 fusion transcripts of several human cell lines. In the fusion transcript, hSAA2 exon 3 was connected to hSAA3 exon 1 or hSAA3 exon 2, located approximately 130kb downstream from hSAA2 exon 3 in the genome, which suggested that it is produced by alternative splicing. Furthermore, we succeeded in detecting and isolating hSAA3 protein for the first time by an immunoprecipitation-enzyme linked immune assay system using monoclonal and polyclonal antibodies that recognize the hSAA3 unique amino acid sequence. We also demonstrated that hSAA3 bound oxidized low density lipoprotein receptor (oxLDL receptor, LOX-1) and elevated the phosphorylation of ERK, the intracellular MAP-kinase signaling protein.

A protective role of ciglitazone in ox-LDL-induced rat microvascular endothelial cells via modulating PPARγ-dependent AMPK/eNOS pathway

Thiazolidinediones, the antidiabetic agents such as ciglitazone, has been proved to be effective in limiting atherosclerotic events. However, the underlying mechanism remains elucidative. Ox-LDL receptor-1 (LOX-1) plays a central role in ox-LDL-mediated atherosclerosis via endothelial nitric oxide synthase (eNOS) uncoupling and nitric oxide reduction. Therefore, we tested the hypothesis that ciglitazone, the PPARγ agonist, protected endothelial cells against ox-LDL through regulating eNOS activity and LOX-1 signalling. In the present study, rat microvascular endothelial cells (RMVECs) were stimulated by ox-LDL. The impact of ciglitazone on cell apoptosis and angiogenesis, eNOS expression and phosphorylation, nitric oxide synthesis and related AMPK, Akt and VEGF signalling pathway were observed. Our data showed that both eNOS and Akt phosphorylation, VEGF expression and nitric oxide production were significantly decreased, RMVECs ageing and apoptosis increased after ox-LDL induction for 24 hrs, all of which were effectively reversed by ciglitazone pre-treatment. Meanwhile, phosphorylation of AMP-activated protein kinase (AMPK) was suppressed by ox-LDL, which was also prevented by ciglitazone. Of interest, AMPK inhibition abolished ciglitazone-mediated eNOS function, nitric oxide synthesis and angiogenesis, and increased RMVECs ageing and apoptosis. Further experiments showed that inhibition of PPARγ significantly suppressed AMPK phosphorylation, eNOS expression and nitric oxide production. Ciglitazone-mediated angiogenesis and reduced cell ageing and apoptosis were reversed. Furthermore, LOX-1 protein expression in RMVECs was suppressed by ciglitazone, but re-enhanced by blocking PPARγ or AMPK. Ox-LDL-induced suppression of eNOS and nitric oxide synthesis were largely prevented by silencing LOX-1. Collectively, these data demonstrate that ciglitazone-mediated PPARγ activation suppresses LOX-1 and moderates AMPK/eNOS pathway, which contributes to endothelial cell survival and function preservation.

Puerarin protects endothelial cells from oxidized low density lipoprotein induced injuries via the suppression of LOX-1 and induction of eNOS

Oxidized low density lipoprotein (oxLDL) induced injury of endothelial cells is considered to be the first step in the pathogenesis of atherosclerosis. This study aimed to investigate some of the effects and mechanisms of puerarin on oxLDL-induced endothelial injuries. We measured cell viability, and the release of lactate dehydrogenase (LDH), nitric oxide (NO), and interleukin-8 (IL-8) to evaluate the protective effects of puerarin. Intracellular reactive oxygen species (ROS) were detected using 2',7'-dichlorofluorescein diacetate (DCFH-DA). The expression of lectin-like low-density lipoprotein receptor-1 (LOX-1), endothelial nitric oxide synthase (eNOS), cyclooxygenase 2 (COX-2), p38MAPK, and protein kinase B (PKB) phosphorylation, nuclear factor-κB (NF-κB) nuclear translocation, and inhibitor of κB (IκB) degradation were detected using quantitative real-time PCR or Western blot. The results showed that oxLDL significantly decreased cell viability, increased LDH and IL-8 release, inhibited NO production, and induced COX-2 expression. Pretreatment with puerarin led to a strong inhibition of these effects. OxLDL stimulated the expression of LOX-1, the overproduction of ROS, the phosphorylation of p38MAPK, the dephosphorylation of PKB, activation of NF-κB, and the degradation of IκB. These oxLDL-induced effects were suppressed after puerarin pretreatment. These results suggest that puerarin inhibits oxLDL-induced endothelial cell injuries, at least in part, via inhibition of the LOX-1-mediated p38MAPK-NF-κB inflammatory and the PKB-eNOS signaling pathways.

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.

High plasma concentrations of asymmetric dimethylarginine inhibit ischemic cardioprotection in hypercholesterolemic rats

A low concentration of nitric oxide associated with a high concentration of asymmetric dimethylarginine (ADMA) can explain the lack of ischemic cardioprotection observed in the presence of hypercholesterolemia. The objective of the present study was to evaluate the effect of hypercholesterolemia on ischemic pre- and postconditioning and its correlation with plasma concentrations of ADMA. Male Wistar rats (6-8 weeks old) fed a 2% cholesterol diet (n = 21) for 8 weeks were compared to controls (n = 25) and were subjected to experimental myocardial infarction and reperfusion, with ischemic pre- and postconditioning. Total cholesterol and ADMA were measured in plasma before the experimental infarct and the infarct area was quantified. Weight, total cholesterol and plasma ADMA (means ± SE; 1.20 ± 0.06, 1.27 ± 0.08 and 1.20 ± 0.08 vs 0.97 ± 0.04, 0.93 ± 0.05 and 0.97 ± 0.04 µM) were higher in animals on the hypercholesterolemic diet than in controls, respectively. Cardioprotection did not reduce infarct size in the hypercholesterolemic animals (pre: 13.55% and post: 8% compared to 7.95% observed in the group subjected only to ischemia and reperfusion), whereas infarct size was reduced in the animals on a normocholesterolemic diet (pre: 8.25% and post: 6.10% compared to 12.31%). Hypercholesterolemia elevated ADMA and eliminated the cardioprotective effects of ischemic pre- and postconditioning in rats.

LOX-1, oxidative stress and inflammation: a novel mechanism for diabetic cardiovascular complications

Diabetes mellitus is a common metabolic disease characterized by a state of oxidative stress, inflammation and endothelial dysfunction. This malady can lead to a number of complications such as ischemic heart disease, nephropathy, neuropathy, retinopathy and impaired wound healing. The etiology of diabetic complications is multifactorial, and is closely associated with oxidative stress and inflammation. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), a receptor for oxidized low density lipoprotein (ox-LDL), plays critical roles in multiple signal transduction pathways and is involved in the process of oxidative stress and inflammation. Recent studies provide important insights into the roles of LOX-1 in the development and progression of diabetic vasculopathy which is the underlying mechanism of diabetic complications. In this review, we summarize mechanistic studies, mainly related to LOX-1, on the development and progression of diabetes mellitus and its cardiovascular complications.

Increased plasma level of asymmetric dimethylarginine in hypertensive rats facilitates platelet aggregation: role of plasma tissue factor

This study was designed to explore the role of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis, in platelet aggregation in hypertension and its possible mechanisms. Spontaneously hypertensive rats (SHR) and L-NAME-induced hypertensive rats were orally administered with L-arginine (1 g/(kg·day) for 14 days. Systolic blood pressure, platelet aggregation, and plasma tissue factor (TF) level and activity were measured. The plasma concentration of ADMA in SHR was determined. In vitro, platelet-rich plasma isolated from Wistar rats was prepared in order to observe the effect of exogenous ADMA on platelet aggregation and TF level and (or) activity in platelet-rich plasma. In both types of hypertensive rats, systolic blood pressure, platelet aggregation, and the level and activity of plasma TF were elevated compared with corresponding control animals. Plasma ADMA level was also increased in SHR. Treatment with L-arginine, a competitor of ADMA, lowered blood pressure and inhibited platelet aggregation concomitantly with a decrease in plasma TF level and activity in both types of hypertensive rats. We also found that exogenous ADMA promoted platelet aggregation and increased TF level and (or) activity in platelet-rich plasma, an effect that was inhibited by pretreatment with L-arginine. Importantly, the enhanced platelet aggregation induced by exogenous ADMA was reduced by pretreatment with anti-TF antibody. The results suggest that endogenous ADMA may be involved in platelet hyperaggregation status in hypertension, and the facilitation of platelet aggregation by ADMA is related to upregulation of the level and activity of plasma TF.

Scavenger receptors of endothelial cells mediate the uptake and cellular proatherogenic effects of carbamylated LDL

OBJECTIVE

Carbamylated LDL (cLDL) has been recently shown to have robust proatherogenic effects on human endothelial cells in vitro, suggesting cLDL may have a significant role in atherosclerosis in uremia. The current study was designed to determine which receptors are used by cLDL and thus cause the proatherogenic effects.

METHODS AND RESULTS

In ex vivo or in vitro models as well as in intact animals, administration of cLDL was associated with endothelial internalization of cLDL and subendothelial translocation (transcytosis). In vitro recombinant LOX-1 and SREC-1 receptors showed the greatest cLDL binding. However, pretreatment of the endothelial cells with specific inhibiting antibodies demonstrated that cLDL binds mainly to LOX-1 and CD36 receptors. The transcytosis was dependent on SR-A1, SREC-1, and CD36 receptors whereas LOX-1 receptor was not involved. The cytotoxicity was mediated by several studied scavenger receptors, but cLDL-induced monocyte adhesion depended only on LOX-1. The cLDL-induced synthesis of LOX-1 protein significantly contributed to both cytotoxicity and accelerated monocyte adhesion to endothelial cells.

CONCLUSIONS

Our data suggest that cLDL uses a unique pattern of scavenger receptors. They show that LOX-1 receptor, and partially CD36, SREC-1, and SR-A1 receptors, are essential for the proatherogenic effects of cLDL on human endothelial cells.

All-trans retinoic acid inhibits cobalt chloride-induced apoptosis in PC12 cells: role of the dimethylarginine dimethylaminohydrolase/asymmetric dimethylarginine pathway

Previous studies have shown that the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and its specific hydrolase dimethylarginine dimethylaminohydrolase (DDAH) are involved in the regulation of apoptosis in different cell types. In the present study, we investigated the role of the DDAH/ADMA pathway in cobalt chloride (CoCl(2))-induced apoptosis and the antiapoptotic effect of all-trans retinoic acid (atRA) in undifferentiated pheochromocytoma (PC12) cells. Treatment of CoCl(2) (125 microM) for 48 hr significantly induced the apoptosis of PC12 cells, concomitantly with increased intracellular reactive oxygen species (ROS) production and caspase-3 activity. CoCl(2) treatment also decreased the activity of DDAH and the expression of DDAH2 (mRNA and protein), resulting in an increased level of ADMA. All these alterations induced by CoCl(2) were attenuated by atRA (0.1, 1, or 10 microM). Interestingly, the antiapoptotic effects of atRA were inhibited by DDAH2 small RNA interference. In contrast, DDAH2 overexpression inhibited the proapoptotic effects of CoCl(2). We also found that treatment of exogenous ADMA (3, 10, or 30 microM) induced the apoptosis of PC12 cells in a concentration- and time-dependent manner, which was inhibited by the antioxidant or the caspase-3 inhibitor. These findings suggest that the modulation of the DDAH/ADMA/ROS pathway plays an important role in CoCl(2)-induced apoptosis and the antiapoptotic effects of atRA in undifferentiated PC12 cells.

Asymmetric dimethylarginine (ADMA) and endothelial dysfunction: implications for atherogenesis

Atherosclerotic coronary heart disease is the leading cause of morbidity and mortality in industrialized countries, and endothelial dysfunction is considered a precursor phenomenon. The nitric oxide produced by the endothelium under the action of endothelial nitric oxide synthase has important antiatherogenic functions. Its reduced bioavailabilty is the beginning of the atherosclerotic process. The addition of two methyl radicals to arginine, through the action of methyltransferase nuclear proteins, produces asymmetric dimethylarginine, which competes with L-arginine and promotes a reduction in nitric oxide formation in the vascular wall. The asymmetric dimethylarginine, which is itself considered a mediator of the vascular effects of the several risk factors for atherosclerosis, can be eliminated by renal excretion or by the enzymatic action of the dimethylarginine dimethylaminohydrolases. Several basic science and clinical research studies suggest that the increase in asymmetric dimethylarginine occurs in the context of chronic renal insufficiency, dyslipidemia, high blood pressure, diabetes mellitus, and hyperhomocysteinemy, as well as with other conditions. Therapeutic measures to combat atherosclerosis may reverse these asymmetric dimethylarginine effects or at least reduce the concentration of this chemical in the blood. Such an effect can be achieved with competitor molecules or by increasing the expression or activity of its degradation enzyme. Studies are in development to establish the true role of asymmetric dimethylarginine as a marker and mediator of atherosclerosis, with possible therapeutic applications. The main aspects of the formation and degradation of asymmetric dimethylarginine and its implication in the atherogenic process will be addressed in this article.

Indolent course of tubulointerstitial disease in a mouse model of subpressor, low-dose nitric oxide synthase inhibition

Deficiency of nitric oxide (NO) represents a consistent manifestation of endothelial dysfunction (ECD), and the accumulation of asymmetric dimethylarginine occurs early in renal disease. Here, we confirmed in vitro and in vivo the previous finding that a fragment of collagen XVIII, endostatin, was upregulated by chronic inhibition of NO production and sought to support a hypothesis that primary ECD contributes to nephrosclerosis in the absence of other profibrotic factors. To emulate more closely the indolent course of ECD, the study was expanded to an in vivo model with N(G)-monomethyl-L-arginine (L-NMMA; mimics effects of asymmetric dimethylarginine) administered to mice in the drinking water at subpressor doses of 0.3 and 0.8 mg/ml for 3-6 mo. This resulted in subtle but significant morphological alterations detected in kidneys of mice chronically treated with L-NMMA: 1) consistent perivascular expansion of interstitial matrix components at the inner stripe of the outer medulla and 2) collagen XVIII/endostatin abundance. Ultrastructural abnormalities were detected in L-NMMA-treated mice: 1) increased activity of the interstitial fibroblasts; 2) occasional detachment of endothelial cells from the basement membrane; 3) splitting of the vascular basement membrane; 4) focal fibrosis; and 5) accumulation of lipofuscin by interstitial fibroblasts. Preembedding labeling of microvasculature with anti-CD31 antibodies showed infiltrating leukocytes and agglomerating platelets attaching to the visibly intact or denuded capillaries. Collectively, the data indicate that the mouse model of subpressor chronic administration of L-NMMA is not a robust one (endothelial pathology visible only ultrastructurally), and yet it closely resembles the natural progression of endothelial dysfunction, microvascular abnormalities, and associated tubulointerstitial scarring.

Serum soluble lectin-like oxidized low-density lipoprotein receptor-1 correlates with oxidative stress markers in stable coronary artery disease

BACKGROUND

Although serum soluble lectin-like oxidized low-density lipoprotein receptor-1 (sLOX-1) is reported to be associated with acute coronary syndrome (ACS), its correlation with oxidative stress markers has not been elucidated. We therefore investigated the association of serum sLOX-1 with the severity of CAD, and serum biomarkers for oxidative stress and inflammation, as well as extracellular superoxide dismutase (EC-SOD), which is protective against oxidative stress in the vascular wall.

METHODS AND RESULTS

Ninety-four patients with stable CAD were enrolled in this study. Serum sLOX-1, serum high-sensitivity C-reactive protein (hs-CRP), urinary 8-isoprostane, plasma BNP and serum lipid levels were measured. We also measured EC-SOD at baseline and post-heparin injection. Heparin-released EC-SOD (DeltaEC-SOD) was calculated as the difference between these two values. No significant correlation was found between log (sLOX-1) and log (basal EC-SOD) (p=0.096), log (hs-CRP) (p=0.108), or log (BNP) (p=0.908) levels, log (sLOX-1) had a significant correlation with DeltaEC-SOD (r=-0.325, p=0.0014) levels and urinary 8-isoprostane levels (r=0.243, p=0.020). In the multivariable analysis, DeltaEC-SOD (p=0.0177) and 8-isoprostane (p=0.0318) were independent predictors for log (sLOX-1).

CONCLUSION

Serum sLOX-1 levels were positively correlated with urinary 8-isoprostane levels and inversely correlated with EC-SOD levels. These results thus suggest that increased serum sLOX-1 levels may reflect enhanced oxidative stress in vascular walls.

Atherogenic scavenger receptor modulation in the tubulointerstitium in response to chronic renal injury

Oxidized low-density lipoproteins (oxLDL) and their scavenger receptor (SR) binding partners play a central role in atherosclerosis and by analogy may play a role in chronic kidney disease pathogenesis. The present study was designed to investigate in C57BL/6 mice the effects of hypercholesterolemia on renal injury severity and oxLDL generation after unilateral ureteral obstruction (UUO). The expression profiles of CD36, SR class AI/II (SR-A), lectin-like receptor for oxidized low-density lipoprotein-1 (Lox-1), and SR that binds phosphatidylserine and oxLDL (SR-PSOX/CXCL16) were examined. Four experimental groups were studied: sham and UUO male mice on either a high-fat Western diet or a control diet. Significantly more oxLDL accumulated in the tubulointerstitium of hypercholesterolemic mice compared with normocholesterolemic mice after 14 days of UUO (P < 0.01). Total kidney collagen was significantly higher in the obstructed kidneys of hypercholesterolemic mice compared with normocholesterolemic mice on day 14 (P < 0.01). After 14 days of obstruction, the number of interstitial F4/80+ macrophages and NF-kappaB activation increased in hypercholesterolemic mice compared with normocholesterolemic mice (P < 0.01). In normal kidneys, CD36, SR-A, Lox-1, and CXCL16 were primarily localized to renal tubular epithelia. After ureteral obstruction, CD36 increased at day 7; SR-A and Lox-1 progressively decreased in a time-dependent manner; and CXCL16 increased significantly with the onset of obstruction (P < 0.01). Strong tubular expression suggests that in addition to inflammatory interstitial cells, renal tubular scavenger receptors may help to orchestrate the inflammatory and fibrogenic pathways that are activated by oxLDL.

Lipoproteins and protection of the arterial wall against infection: the "response to the threat of infection" hypothesis

The exact reason why lipoproteins are found in the arterial intima is not understood. On the basis of recent findings presented in the literature, we are proposing a hypothesis that the accumulation of lipoprotein in the arterial intima is originally a physiological process, part of our defences against infection designed to protect susceptible segments of the arterial wall from microbial invasion. In addition to the intrinsic antimicrobial activities of the deposited lipids, the formation of fibrin-based matrices within the intima is promoted, fibrinolysis is inhibited, the lipid content exerts a vasoconstrictive influence and smooth muscle cells are mobilised into the intima, all these phenomenons being instrumental in fighting off an infectious menace. Oxidized lipids (including oxysterols and lysophosphatidylcholine) resulting from the oxidation of lipoproteins close to sites of infection and inflammation are disseminated through the circulatory system and act as alarm signals at arterial walls, promoting the penetration and retention of lipoproteins in the intimal tissue of the most susceptible segments of the arterial network. Oxidized lipids in the intima constitute part of first-line antimicrobial defences and their presence acts as a signal to immune effector cells (notably macrophages and lymphocytes) which trigger the acquired immune response when foreign antigens are encountered.

MgSO4 prevents left ventricular dysfunction in an animal model of preeclampsia

OBJECTIVE

We hypothesized that cardiac function would be reduced in a pregnant rat model of preeclampsia induced by L-NAME, a NOS inhibitor, and be reversed with magnesium sulfate prophylaxis.

STUDY DESIGN

Female Sprague-Dawley rats were bred in-house. On gestational day 17, rats were anesthetized and osmotic minipumps were implanted to continuously deliver saline, L-NAME, or L-NAME and MgSO4. On gestational day 21, hearts were isolated and perfused in the working mode using Krebs Henseleit buffer.

RESULTS

Pregnant rats treated with L-NAME displayed significant hypertension compared to the saline-treated controls (P < 0.05). Moreover, cardiac output and cardiac work were significantly reduced in the L-NAME-treated rats compared to controls (P < 0.05). In the L-NAME-treated rats given MgSO4, cardiac function remained normal.

CONCLUSION

Cardiac function is depressed in an animal model of preeclampsia induced by L-NAME infusion. MgSO4 prevented the reduction in cardiac function and is clearly beneficial in preserving normal heart function in preeclampsia.

The Clinical Significance of Asymmetric Dimethylarginine

In 1992, asymmetrical dimethylarginine (ADMA) was first described as an endogenous inhibitor of the arginine-nitric oxide (NO) pathway. From then, its role in regulating NO production has attracted increasing attention. Nowadays, ADMA is regarded as a novel cardiovascular risk factor. The role of the kidney and the liver in the metabolism of ADMA has been extensively studied and both organs have proven to play a key role in the elimination of ADMA. Although the liver removes ADMA exclusively via degradation by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), the kidney uses both metabolic degradation via DDAH and urinary excretion to eliminate ADMA. Modulating activity and/or expression of DDAH is still under research and may be a potential therapeutic approach to influence ADMA plasma levels. Interestingly, next to its association with cardiovascular disease, ADMA also seems to play a role in other clinical conditions, such as critical illness, hepatic failure, and preeclampsia. To elucidate the clinical significance of ADMA in these conditions, the field of research must be enlarged.

Oxidative stress in diabetes: A mechanistic overview of its effects on atherogenesis and myocardial dysfunction

Diabetes is a major risk factor for atherosclerosis. Atherogenesis involves endothelial dysfunction, activation and injury, inflammation, and smooth muscle cell migration and proliferation. Platelet activation in the narrowed arteries is the most proximate event in the culmination of an acute event such as acute myocardial infraction and stroke. Hyperglycemia is associated with all these adverse events in the process of genesis of atherosclerosis. The effect of diabetes (hyperglycemia) is mediated in large part by the state of enhanced oxidative stress, which is not counter-balanced by endogenous antioxidants. This paper reviews the ignition of oxidative stress in diabetes and the mediation of events leading to atherogenesis.

Oxidized low density lipoprotein impairs endothelial progenitor cells by regulation of endothelial nitric oxide synthase

Oxidized low density lipoprotein (OxLDL) is one of the most important risk factors of cardiovascular disease. Here, we study the impact of OxLDL on endothelial progenitor cells (EPCs) and determine whether OxLDL affects EPCs by an inhibitory effect on endothelial nitric oxide synthase (eNOS). It was found that OxLDL decreased EPC survival and impaired its adhesive, migratory, and tube-formation capacities in a dose-dependent manner. However, all of the detrimental effects of OxLDL were attenuated by pretreatment of EPCs with lectin-like oxidized low density lipoprotein receptor (LOX-1) monoclonal antibody or l-arginine. Western blot analysis revealed that OxLDL dose-dependently decreased Akt phosphorylation and eNOS protein expression and increased LOX-1 protein expression. Furthermore, OxLDL caused a decrease in eNOS mRNA expression and an increase in LOX-1 mRNA expression. These data indicate that OxLDL inhibits EPC survival and impairs its function, and this action is attributable to an inhibitory effect on eNOS.

Asymmetric dimethylarginine induces apoptosis via p38 MAPK/caspase-3-dependent signaling pathway in endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), is emerging as a key contributor for endothelial dysfunction and its effects on endothelium are not yet completely defined. The aim of this study was to investigate ADMA-induced apoptosis and its mechanisms in human umbilical vein endothelial cells (HUVECs). Apoptosis was evaluated by in situ terminal uridine nick end labeling (TUNEL) assay and DNA fragmentation analysis. Caspase-3 activity was measured using a colorimetric protease assay kit. Activations of mitogen-activated protein kinases (MAPKs) were characterized by Western blot and immunofluorescence. Intracellular oxidant production was measured using H(2)DCF-DA, an oxidant-sensitive fluorescent indicator. ADMA (3-30 microM) induced apoptosis of HUVECs in a dose- and time-dependent manner. Caspase-3 was activated during apoptosis and its specific inhibitor DEVD-CHO significantly attenuated ADMA-induced apoptosis. Phosphorylation of p38 MAPK was induced by ADMA, and p38 MAPK specific inhibitor SB203580 concentration-dependently prevented ADMA-induced caspase-3 activation and cell apoptosis. ADMA increased intracellular oxidant production, which was significantly suppressed by intracellular antioxidant PDTC, l-arginine or antisense endothelial NOS mRNA. They also markedly prevented ADMA-induced phosphorylation of p38 MAPK and cell apoptosis. In conclusion, our present results demonstrate that ADMA induces apoptosis of endothelial cell via elevation of intracellular oxidant production, which involves p38 MAPK/caspase-3-dependent signaling pathway.

Impact of oxidized low density lipoprotein on vascular cells

Oxidized LDL (OxLDL) is a proatherogenic lipoprotein, accumulating in the vascular wall and contributing to the pathogenesis of vascular dysfunction early in the development of atherosclerosis. Enhanced serum levels of OxLDL, as well as antibodies against its epitopes, are predictive for endothelial dysfunction and coronary heart disease. While enhanced oxidative stress is one factor triggering formation of OxLDL, OxLDL itself has been identified as a potent stimulus for vascular oxygen radical formation, causing a vicious circle. OxLDL-induced O(2)(-) formation, largely through activation of NADPH oxidase, but also through uncoupling of endothelial NO-synthase and through direct O(2)(-) release, leads to endothelial dysfunction. Furthermore, OxLDL-induced O(2)(-) formation has a strong impact on tissue remodeling, resulting in either cell growth - proliferation or hyperplasia - or apoptotic cell death. The effect of OxLDL on cell cycle regulation is mediated by activation of the small GTPase RhoA and consequent regulation of p27(KIP1), a key enzyme of the cell cycle. In addition, OxLDL-induced activation of RhoA sensitizes the contractile apparatus of the vessel wall, enhancing the contractile tonus and favoring vasospasm. Thus, through a variety of mechanisms, OxLDL importantly contributes to vascular dysfunction and remodeling.

Endothelial cell dysfunction: can't live with it, how to live without it

Endothelial cell dysfunction is emerging as an ultimate culprit for diverse cardiovascular diseases and cardiovascular complications of chronic renal diseases, yet the definition of this new syndrome, its pathophysiology, and therapy remain poorly defined. Here, I summarize some molecular mechanisms leading from hyperhomocystinemia, elevated asymmetric dimethylarginine, and advanced glycolation end product-modified protein level to the proatherogenic, prothrombogenic, and proinflammatory endothelial phenotype and offer a model of endothelial dysfunction based on the interconnectedness of diverse functions. Finally, several therapeutic strategies to prevent and correct endothelial dysfunction are discussed in the light of uncertainty of their action modulated by the endothelial dysfunction per se.

What have we learnt about microarray analyses of atherogenesis?

PURPOSE OF REVIEW

This review covers recent developments in microarray studies in the field of atherogenesis research.

RECENT FINDINGS

During the past year microarrays have been applied to the analysis of pathogenic mechanisms of several atherosclerosis risk factors, including ageing, hypertension, obesity, and cytomegalovirus infection. In addition, gene expression patterns during the development of in-stent restenosis have been examined. Several studies have also explored the pleiotropic effects of statin therapy. As a technical improvement, the combination of laser microdissection with microarrays in human samples has been reported.

SUMMARY

Microarray analyses have given important new information about atherogenesis. It is anticipated that microarray studies will significantly contribute to further discoveries in the field.

Genetics, genomics and proteomics in atherosclerosis research

Atherosclerosis and its clinical manifestations are the leading cause of death in Western countries. Atherosclerosis is a multifactorial disease characterized by endothelial dysfunction, smooth muscle cell (SMC) proliferation and migration, inflammation, lipid and matrix accumulation and thrombus formation. Multiple genetic and environmental features and interactions between these factors influence the disease process. To understand fundamental pathobiological mechanisms in atherogenesis and to develop and target new therapies, information on genetic factors (atherogenetics), gene expression patterns (atherogenomics) and protein expression patterns (atheroproteomics) are needed. This review will summarize current knowledge in these areas of atherosclerosis research with a special emphasis on microarray technology.