Critical role of the nitric oxide/reactive oxygen species balance in endothelial progenitor dysfunction

Interactions between inflammatory activation and endothelial dysfunction selectively modulate valve disease progression in patients with bicuspid aortic valve

OBJECTIVES

Bicuspid aortic valve (BAV) is associated with increased risk of valvular degeneration and ascending aortic aneurysm formation and rupture. We sought to evaluate the roles of endothelial dysfunction and inflammatory activation in modulating these processes.

METHODS

We performed a case-control study of patients with BAV together with a multivariate analysis within the BAV group to identify factors associated with: development of significant valvular disease; dilatation of the ascending aorta; differential valve relative to aortic disease. Endothelial function of patients and controls was evaluated via flow-mediated dilatation (FMD) and plasma concentrations of asymmetric dimethylarginine (ADMA). Correlations with inflammatory markers and endothelial progenitor cell counts were also examined. Morphological and physiological assessment of the valve and ascending aorta was performed with transthoracic echocardiography and MRI.

RESULTS

Patients with BAV (n=43) and controls (n=25) were matched for age and gender. FMD was significantly lower in patients than controls (7.85±3.48% vs 11.58±3.98%, p=0.001), and these differences were age-independent. Within the BAV cohort, multivariate correlates of peak aortic valve velocity were plasma concentrations of ADMA and myeloperoxidase (MPO) (both p<0.01), while increasing age was an independent correlate of ascending aortic diameter (p<0.05). Furthermore, both low FMD and inflammatory activation were multivariate correlates of selectivity for valvular disease.

CONCLUSIONS

BAV is associated with endothelial dysfunction. The extent of inflammatory activation (specifically MPO release) and that of endothelial dysfunction impact primarily on integrity of the valve rather than aortic structure.

Targeting inflammation and oxidative stress in atrial fibrillation: role of 3-hydroxy-3-methylglutaryl-coenzyme a reductase inhibition with statins

SIGNIFICANCE

Atrial fibrillation (AF) is a burgeoning health-care problem, and the currently available therapeutic armamentarium is barely efficient. Experimental and clinical evidence implicates inflammation and myocardial oxidative stress in the pathogenesis of AF.

RECENT ADVANCES

Local and systemic inflammation has been found to both precede and follow the new onset of AF, and NOX2-dependent generation of reactive oxygen species in human right atrial samples has been independently associated with the occurrence of AF in the postoperative period in patients undergoing cardiac surgery. Anti-inflammatory and antioxidant agents can prevent atrial electrical remodeling in animal models of atrial tachypacing and the new onset of AF after cardiac surgery, suggesting a causal relationship between inflammation/oxidative stress and the atrial substrate that supports AF.

CRITICAL ISSUES

Statin therapy, by redressing the myocardial nitroso-redox balance and reducing inflammation, has emerged as a potentially effective strategy for the prevention of AF. Evidence indicates that statins prevent AF-induced electrical remodeling in animal models of atrial tachypacing and may reduce the new onset of AF after cardiac surgery. However, whether statins have antiarrhythmic properties in humans has yet to be conclusively demonstrated, as data from randomized controlled trials specifically addressing the relevance of statin therapy for the primary and secondary prevention of AF remain scanty.

FUTURE DIRECTIONS

A better understanding of the mechanisms underpinning the putative antiarrhythmic effects of statins may afford tailoring AF treatment to specific clinical settings and patient's subgroups. Large-scale randomized clinical trials are needed to support the indication of statin therapy solely on the basis of AF prevention.

Ischemic preconditioning for cell-based therapy and tissue engineering

Cell- and tissue-based therapies are innovative strategies to repair and regenerate injured hearts. Despite major advances achieved in optimizing these strategies in terms of cell source and delivery method, the clinical outcome of cell-based therapy remains unsatisfactory. The non-genetic approach of ischemic/hypoxic preconditioning to enhance cell- and tissue-based therapies has received much attention in recent years due to its non-invasive drug-free application. Here we discuss the current development of hypoxic/ischemic preconditioning to enhance stem cell-based cardiac repair and regeneration.

Reduced circulating endothelial progenitor cells in thromboangiitis obliterans (Buerger’s disease)

To determine the role of endothelial progenitor cells (EPCs) in the pathogenesis of thromboangiitis obliterans (TAO), EPC numbers and colony-forming units, migratory function and tubular structure formation in vitro were compared between 13 young male TAO patients and two age-matched healthy control groups: 11 smokers and 12 non-smokers. TAO patients had significantly lower numbers of EPCs and EPC colonies compared to both non-smokers [190 (97.0–229) vs 528 (380–556), p < 0.001 for EPCs and 0.80 (0.53–1.00) vs 2.80 (2.08–4.00) per mm2, p = 0.001 for EPC colonies] and smokers [190 (97.0–229) vs 272 (229–326), p = 0.012 for EPCs and 0.80 (0.53–1.00) vs 2.80 (1.80–3.93) per mm2, p = 0.001 for EPC colonies]. However, there were no significant differences in migratory function or tube formation between the three groups. These results suggest that TAO patients have an intrinsic decrease in EPCs not entirely associated with smoking, which may be the cause of endothelial dysfunction seen in TAO patients leading to the development of this disease at early ages.

Microparticles and microRNAs of endothelial progenitor cells ameliorate acute kidney injury

Horizontal information transfer between cells via microparticles is a newly identified communication system. MicroRNAs regulate gene expression and are detected in microparticles. The article by Cantaluppi et al. suggests that microparticles derived from circulating angiogenic cells (“endothelial progenitor cells”, EPC) harbor endothelial-protective miRNAs such as miR-126 and that delivery of EPC-derived microparticles during acute kidney ischemia-reperfusion in rats ameliorates kidney dysfunction and damage. We highlight the importance, future impact and limitations of this study.

Chlamydia pneumoniae infection in atherosclerotic lesion development through oxidative stress: a brief overview

Chlamydia pneumoniae, an obligate intracellular pathogen, is known as a leading cause of respiratory tract infections and, in the last two decades, has been widely associated with atherosclerosis by seroepidemiological studies, and direct detection of the microorganism within atheroma. C. pneumoniae is presumed to play a role in atherosclerosis for its ability to disseminate via peripheral blood mononuclear cells, to replicate and persist within vascular cells, and for its pro-inflammatory and angiogenic effects. Once inside the vascular tissue, C. pneumoniae infection has been shown to induce the production of reactive oxygen species in all the cells involved in atherosclerotic process such as macrophages, platelets, endothelial cells, and vascular smooth muscle cells, leading to oxidative stress. The aim of this review is to summarize the data linking C. pneumoniae-induced oxidative stress to atherosclerotic lesion development.

Oxidative stress-mediated thrombospondin-2 upregulation impairs bone marrow-derived angiogenic cell function in diabetes mellitus

OBJECTIVE

Circulating angiogenic cells play an essential role in angiogenesis but are dysfunctional in diabetes mellitus characterized by excessive oxidative stress. We hypothesize that oxidative stress-mediated upregulation of thrombospondin-2 (TSP-2), a potent antiangiogenic protein, contributes to diabetic bone marrow-derived angiogenic cell (BMAC) dysfunction.

APPROACH AND RESULTS

BMACs were isolated from adult male type 2 diabetic db/db mice and control db/+ (C57BLKS/J) mice. In Matrigel tube formation assay, angiogenic function was impaired in diabetic BMACs, accompanied by increased oxidative stress and nicotinamide adenine dinucleotide phosphate oxidase activity. BMAC angiogenic function was restored by overexpression of dominant negative Rac1 or by overexpression of manganese superoxide dismutase. TSP-2 mRNA and protein were both significantly upregulated in diabetic BMACs, mediated by increased oxidative stress as shown by a decrease in TSP-2 level after overexpression of dominant negative Rac1 or manganese superoxide dismutase. Silencing TSP-2 by its small interfering RNA in diabetic BMACs improved BMAC function in tube formation, adhesion, and migration assays. Notably, the upregulation of TSP-2 was also found in BMACs from streptozotocin-induced type 1 diabetic mice, and normal BMACs with high glucose treatment. let-7f, a microRNA which has been related to endothelial angiogenic function, is found to play key role in TSP-2 increase, but let-7f did not directly interact with TSP-2 mRNA.

CONCLUSIONS

The upregulation of TSP-2 mediated by increased oxidative stress contributes to angiogenesis dysfunction in diabetic BMACs.

Low clonogenic potential of circulating angiogenic cells is associated with lower density of capillaries in skeletal muscle in patients with impaired glucose tolerance

BACKGROUND

Reduced density of capillaries in skeletal muscle can limit insulin, glucose, and oxygen supply to the muscle, thereby contributing to worsening metabolism in older adults. The lower skeletal muscle capillarization in impaired glucose tolerance (IGT) may partially be due to circulating angiogenic cell dysfunction. Circulating angiogenic cells maintain the vasculature and promote angiogenesis, but circulating angiogenic cell number and function may be reduced in IGT. The goal of this study was to determine whether the clonogenic potential of circulating angiogenic cells is lower in IGT compared with normal-glucose-tolerant (NGT) controls and is associated with skeletal muscle capillarization.

METHODS

Glucose tolerance, endothelial cell colony-forming unit (CFU-EC) number, and vastus lateralis capillary density were measured in sedentary, older (62 ± 1 years, mean ± SEM) men and women with NGT (n = 16) and IGT (n = 12).

RESULTS

Adults with IGT had 43% lower CFU-EC number (11.4 ± 2.3 versus 20.1 ± 2.0 colonies, p < 0.01) and 12% lower capillary density (291 ± 11 versus 330 ± 9 capillaries/mm², p < 0.01) compared with those with NGT. In regression analyses, CFU-EC number inversely correlated with 120-min postprandial glucose in all subjects (r = -0.47, p < 0.05), and capillary density was directly associated with CFU-EC number (r = 0.53, p < 0.05).

CONCLUSIONS

We conclude that the clonogenic potential of circulating angiogenic cells is lower in sedentary older adults with IGT and is associated with lower skeletal muscle capillarization. Low circulating angiogenic cell clonogenic potential in IGT suggests a state of impaired angiogenesis occurring prior to overt type 2 diabetes that may mediate early microvascular changes in the development and progression of IGT to type 2 diabetes.

Endothelial progenitor cell dysfunction in cardiovascular diseases: role of reactive oxygen species and inflammation

Endothelial progenitor cells (EPCs) move towards injured endothelium or inflamed tissues and incorporate into foci of neovascularisation, thereby improving blood flow and tissue repair. Patients with cardiovascular diseases have been shown to exhibit reduced EPC number and function. It has become increasingly apparent that these changes may be effected in response to enhanced oxidative stress, possibly as a result of systemic and localised inflammatory responses. The interplay between inflammation and oxidative stress affects the initiation, progression, and complications of cardiovascular diseases. Recent studies suggest that inflammation and oxidative stress modulate EPC bioactivity. Clinical medications with anti-inflammatory and antioxidant properties, such as statins, thiazolidinediones, angiotensin II receptor 1 blockers, and angiotensin-converting enzyme inhibitors, are currently administered to patients with cardiovascular diseases. These medications appear to exert beneficial effects on EPC biology. This review focuses on EPC biology and explores the links between oxidative stress, inflammation, and development of cardiovascular diseases.

The potential of flavanol and procyanidin intake to influence age-related vascular disease

Advancing age is an independent major risk factor for cardiovascular disease (CVD). Age-associated impairments in the control of inflammation, excessive oxidative stress, and reduced cellular repair can all contribute to the development and progression of CVD. Current recommendations for both the primary and secondary prevention of CVD promote lifestyle modifications that include the adoption of healthy dietary patterns, such as the consumption of diets rich in plant foods, as these have been associated with a lower lifetime risk for the development of CVD. The potential for a diet rich in plant foods to be cardiovascular protective is also supported by prospective studies that suggest the intake of foods providing high amounts of certain phytochemicals, in particular flavanols and procyanidins, reduce the risk for CVD. These observations are further supported by a number of dietary intervention trials that show improvements in vascular function and reduced platelet reactivity following the consumption of high flavanol foods. In the current article we review a selection of these studies, and comment on some of the potential mechanisms that have been postulated to underlie the health effects of flavanol and procyanidin-rich foods.

Pathologic endothelial response and impaired function of circulating angiogenic cells in patients with Fabry disease

Fabry disease is an X-chromosomal recessive deficiency of the lysosomal hydrolase alpha-galactosidase A (alpha-Gal). This results in an accumulation of globotriaosylceramide (GL-3) in a variety of cells often with subsequent functional impairment. Here, the impact of Fabry disease on the biology of circulating angiogenic cells (CACs) and the endothelial response to transient ischemia was investigated. Untreated patients with Fabry disease (n = 26), patients after initiation of alpha-Gal enzyme replacement therapy (ERT) (n = 16) and healthy controls (n = 26) were investigated. Endothelial function was assessed by the EndoPAT2000 device. CAC numbers were assessed by flow-cytometry, CAC function by a modified Boyden chamber assay. Fabry patients showed a pathologic endothelial response, which normalized after ERT. CACs were increased in number, but functionally impaired. Immunofluorescence and electron microscopy identified an accumulation of GL-3 in Fabry CACs. ERT attenuated CAC dysfunction and improved markers of oxidative stress response in Fabry patients via a reduction in GL-3 accumulation in vitro and in vivo. Silencing of alpha-Gal in healthy CACs impaired their migratory capacity underlining a key role of this enzyme for CAC function. CAC supernatant as well as CACs from Fabry patients impaired angiogenesis and migratory capacity of HUVECs providing a mechanistic link between CAC and endothelial dysfunction. CAC adhesion to TNF-α pre-stimulated HUVECs and tube formation was impaired by alpha-Gal knockdown. Fabry patients show a dysfunction of CAC and a pathologic endothelial response. ERT improves CAC and endothelial function and thus may attenuate development of cardiovascular disease in the long term in this patient population.

Tackling endothelial dysfunction by modulating NOS uncoupling: new insights into its pathogenesis and therapeutic possibilities

Endothelial nitric oxide synthase (eNOS) serves as a critical enzyme in maintaining vascular pressure by producing nitric oxide (NO); hence, it has a crucial role in the regulation of endothelial function. The bioavailability of eNOS-derived NO is crucial for this function and might be affected at multiple levels. Uncoupling of eNOS, with subsequently less NO and more superoxide generation, is one of the major underlying causes of endothelial dysfunction found in atherosclerosis, diabetes, hypertension, cigarette smoking, hyperhomocysteinemia, and ischemia/reperfusion injury. Therefore, modulating eNOS uncoupling by stabilizing eNOS activity, enhancing its substrate, cofactors, and transcription, and reversing uncoupled eNOS are attractive therapeutic approaches to improve endothelial function. This review provides an extensive overview of the important role of eNOS uncoupling in the pathogenesis of endothelial dysfunction and the potential therapeutic interventions to modulate eNOS for tackling endothelial dysfunction.

Fast reduction of peripheral blood endothelial progenitor cells in healthy humans exposed to acute systemic hypoxia

There are hints that hypoxia exposure may affect the number of circulating endothelial progenitor cells (EPCs) in humans. To test this hypothesis, the concentration of EPCs was determined by flow cytometry in the peripheral blood of 10 young healthy adults before (0 h), at different times (0.5 h, 1 h, 2 h and 4 h) during a 4 h normobaric hypoxic breathing simulating 4100 m altitude, and in the following recovery breathing room air. Results were interpreted mainly on the basis of the changes in surface expression of CXC chemokine receptor-4 (CXCR-4, a chemokine receptor essential for EPC migration and homing) and the percentage of apoptotic cells, the plasmatic levels of markers of oxidative stress induced by hypoxic breathing. Compared to 0 h, the concentration of EPCs, identified as either CD45(dim)/CD34(+)/KDR(+) or CD45(dim)/CD34(+)/KDR(+)/CD133(+) cells, decreased from 337 ± 83 ml(-1) (mean ± SEM) to 223 ± 52 ml(-1) (0.5 h; P < 0.005) and 100 ± 37 ml(-1) (4 h; P < 0.005), and from 216 ± 91 to 161 ± 50 ml(-1) (0.5 h; P < 0.05) and 45 ± 23 ml(-1) (4 h; P < 0.005), respectively. Upon return to normoxia, their concentration increased slowly, and after 4 h was still lower than at 0 h (P < 0.05). During hypoxia, CXCR-4 expression and plasmatic stromal derived cell factor-1 (SDF-1) increased abruptly (0.5 h: +126% and +13%, respectively; P < 0.05), suggesting cell marginalization as a possible cause of the rapid hypoxia-induced EPC reduction. Moreover, hypoxia exposure induced an increase in EPC apoptosis and markers of oxidative stress, which was significantly evident only starting from 2 h and 4 h after hypoxia offset, respectively, suggesting that EPC apoptosis may contribute to the later phase of hypoxia-induced EPC reduction. Overall, these observations may provide new insights into the understanding of the mechanisms operated by EPCs to maintain endothelial homeostasis.

Endothelial progenitor cells=EPC=elemental pernicious complexity

Endothelial progenitor cells (EPCs) represent a heterogeneous population of cells with a pro-angiogenic potential that are derived not only from bone marrow but also from other tissues. Depending on the model and cell type used, the pro-angiogenic effect is a consequence of direct vascular integration, the paracrine release of growth factors and cytokines, or complex interactions with other cellular components like monocytes or platelets. The pro-angiogenic potential of EPCs is dependent on the particular type of EPC studied and modulated by the risk and life style factors of the patient as well as by local factors determining the homing to diseased tissue and the EPC proteome. In this Forum on EPCs these aspects will be covered in individual review articles, which are accompanied by two original research studies on the role of NADPH oxidases for EPC mobilization and the impact of organic nitrates on EPCs.

Effects of acute and chronic endurance exercise on intracellular nitric oxide and superoxide in circulating CD34⁺ and CD34⁻ cells

We investigated the influence of acute and chronic endurance exercise on levels of intracellular nitric oxide (NO), superoxide (O₂·⁻), and expression of genes regulating the balance between these free radicals in CD34⁺ and CD34⁻ peripheral blood mononuclear cells (PBMCs; isolated by immunomagnetic cell separation). Blood samples were obtained from age- and body mass index (BMI)-matched endurance-trained (n = 10) and sedentary (n = 10) men before and after 30 min of exercise at 75% maximal oxygen uptake (·VO(₂max)). Baseline levels of intracellular NO (measured by DAF-FM diacetate) and O₂·⁻ (measured by dihydroethidium) were 26% (P < 0.05) and 10% (P < 0.05) higher, respectively, in CD34⁺ PBMCs from the sedentary group compared with the endurance-trained group. CD34⁺ PBMCs from the sedentary group at baseline had twofold greater inducible nitric oxide synthase (iNOS) mRNA and 50% lower endothelial NOS (eNOS) mRNA levels compared with the trained group (P < 0.05). The baseline group difference in O₂·⁻ was eliminated by acute exercise. Experiments with apocynin indicated that the training-related difference in O₂·⁻ levels was explained by increased NADPH oxidase activity in the sedentary state. mRNA levels of additional angiogenic and antioxidant genes were consistent with a more angiogenic profile in CD34⁺ cells of trained subjects. CD34⁻ PBMCs, examined for exploratory purposes, also displayed a more angiogenic mRNA profile in trained subjects, with vascular endothelial growth factor (VEGF) and eNOS being more highly expressed in trained subjects. Overall, our data suggest an association between the sedentary state and increased nitro-oxidative stress in CD34⁺ cells.

Smoke exposure and circulating progenitor cells: evidence for modulation of antioxidant enzymes and cell count

BACKGROUND

Cigarette smoking is involved in vascular inflammation and impairment of circulating progenitor cells (CPCs), including endothelial progenitor cells (EPCs). The study aim was to evaluate the redox balance of these cells in relation to smoking exposure.

METHODS

Circulating cells from 36 healthy smokers and 26 controls were isolated and identified by flow cytometry. ROS generation, mRNA and protein cell expression, and enzymatic activity of MnSOD, catalase, and GPx-1 were evaluated.

RESULTS

Smokers showed higher levels of CRP and fibrinogen and lower levels of HDL-C. ROS and MnSOD were higher (p<0.001), while catalase and GPx-1 were lower (p<0.001) as was EPC number (p<0.001) in smokers. CPC and EPC correlated with HDL-C, CRP, ROS and enzyme expression and activity.

CONCLUSIONS

Our data suggest that smoking exposure involves antioxidant enzymes in CPCs and EPCs and that the inflammatory response in smokers plays an important role in impairing cells and their antioxidant functions.