Decrease of plasma vitamin E (alpha-tocopherol) levels in patients with abdominal aortic aneurysm

Oxidative Stress and the Pathogenesis of Aortic Aneurysms

Aortic aneurysms are responsible for significant morbidity and mortality. Despite their clinical significance, there remain critical knowledge gaps in the pathogenesis of aneurysm disease and the mechanisms involved in aortic rupture. Recent studies have drawn attention to the role of reactive oxygen species (ROS) and their down-stream effectors in chronic cardiovascular diseases and specifically in the pathogenesis of aortic aneurysm formation. This review will discuss current mechanisms of ROS in mediating aortic aneurysms, the failure of endogenous antioxidant systems in chronic vascular diseases, and their relation to the development of aortic aneurysms.

Disturbed hemodynamics and oxidative stress interaction in endothelial dysfunction and AAA progression: Focus on Nrf2 pathway

Hemodynamic shear stress is one of the major factors that are involved in the pathogenesis of many cardiovascular diseases including atherosclerosis and abdominal aortic aneurysm (AAA), through its modulatory effect on the endothelial cell's redox homeostasis and mechanosensitive gene expression. Among important mechanisms, oxidative stress, endoplasmic reticulum stress activation, and the subsequent endothelial dysfunction are attributed to disturbed blood flow and low shear stress in the vascular curvature and bifurcations which are considered atheroprone regions and aneurysm occurrence spots. Many pathways were shown to be involved in AAA progression. Of particular interest from recent findings is, the (Nrf2)/Keap-1 pathway, where Nrf2 is a transcription factor that has antioxidant properties and is strongly associated with several CVDs, yet, the exact mechanism by which Nrf2 alleviates CVDs still to be elucidated. Nrf2 expression is closely affected by shear stress and was shown to participate in AAA. In the current review paper, we discussed the link between disturbed hemodynamics and its effect on Nrf2 as a mechanosensitive gene and its role in the development of endothelial dysfunction which is linked to the progression of AAA.

Systemic oxidant/antioxidant balance in human abdominal aortic aneurysm

The aim of this study was to evaluate the oxidant-antioxidant balance in patients with abdominal aortic aneurysms (AAA). Forty-two consecutive patients with AAA and 46 control subjects were included. Total oxidant status (TOS) and total antioxidant status (TAS) levels were measured and the oxidative stress index (OSI) value determined. Serum TOS and OSI values in patients with AAA were higher than those in the controls (p<0.001, p<0.001, respectively). There was a positive correlation between abdominal aortic diameters, serum TOS levels (r=0.592, p<0.001) and OSI values (r=0.598, p<0.001). A cut-off value of 17.68 µmol H2O2 equivalent/L for TOS was associated with 86% sensitivity and 83% specificity and a cut-off value of 1.77 for OSI was associated with 86% sensitivity and 81% specificity for predicting AAA. Systemic oxidative imbalance develops in patients with AAA, particularly as a result of an increase in TOS.

Impaired high-density lipoprotein anti-oxidant capacity in human abdominal aortic aneurysm

AIMS

Abdominal aortic aneurysm (AAA) is a particular form of atherothrombotic disease characterized by the dilation of the aortic wall and the presence of an intraluminal thrombus (ILT). The objective of the present study was to evaluate the pro-oxidant properties of the ILT and to characterize the anti-oxidant capacity of high-density lipoproteins (HDLs).

METHODS AND RESULTS

Our results show that ILT, adventitia, and plasma from AAA patients contained high concentrations of lipid and protein oxidation products. Mediators produced within or released by the thrombus and the adventitia were shown to induce reactive oxygen species (ROS) production by cultured aortic smooth muscle cells (AoSMCs) and to trigger the onset of apoptosis (an increase in mitochondrial membrane potential). Iron chelation limited these effects. Both concentration and functionality of HDLs were altered in AAA patients. Plasma levels of Apo A-I were lower, and small HDL subclasses were decreased in AAA patients. Circulating HDLs in AAA patients displayed an impaired capacity to inhibit copper-induced low-density lipoprotein oxidation and AoSMC ROS production. Western blot analyses of HDLs demonstrated that myeloperoxidase is associated with HDL particles in AAA patients.

CONCLUSION

ILT and adventitia are a source of pro-oxidant products, in particular haemoglobin, which may impact on the wall stability/rupture in AAA. In addition, HDLs from AAA patients exhibit an impaired anti-oxidant activity. In this context, restoring HDL functionality may represent a new therapeutic option in AAA.

Overexpression of catalase in vascular smooth muscle cells prevents the formation of abdominal aortic aneurysms

OBJECTIVE

Elevated levels of oxidative stress have been reported in abdominal aortic aneurysms (AAA), but which reactive oxygen species promotes the development of AAA remains unclear. Here, we investigate the effect of hydrogen peroxide (H2O2)-degrading enzyme catalase on the formation of AAA.

APPROACH AND RESULTS

AAA were induced with the application of calcium chloride (CaCl2) on mouse infrarenal aortas. The administration of PEG-catalase, but not saline, attenuated the loss of tunica media and protected against AAA formation (0.91 ± 0.1 versus 0.76 ± 0.09 mm). Similarly, in a transgenic mouse model, catalase overexpression in the vascular smooth muscle cells preserved the thickness of tunica media and inhibited aortic dilatation by 50% (0.85 ± 0.14 versus 0.57 ± 0.08 mm). Further studies showed that injury with CaCl2 decreased catalase expression and activity in the aortic wall. Pharmacological administration or genetic overexpression of catalase restored catalase activity and subsequently decreased matrix metalloproteinase activity. In addition, a profound reduction in inflammatory markers and vascular smooth muscle cell apoptosis was evident in aortas of catalase-overexpressing mice. Interestingly, as opposed to infusion of PEG-catalase, chronic overexpression of catalase in vascular smooth muscle cells did not alter the total aortic H2O2 levels.

CONCLUSIONS

The data suggest that a reduction in aortic wall catalase activity can predispose to AAA formation. Restoration of catalase activity in the vascular wall enhances aortic vascular smooth muscle cell survival and prevents AAA formation primarily through modulation of matrix metalloproteinase activity.

On the potential increase of the oxidative stress status in patients with abdominal aortic aneurysm

BACKGROUND

Abdominal aortic aneurysm (AAA) is a major cause of preventable deaths in older patients. Oxidative stress has been suggested to play a key role in the pathogenesis of AAA. However, only few studies have been conducted to evaluate the blood oxidative stress status of AAA patients.

METHODS AND RESULTS

Twenty seven AAA patients (mean age of 70 years) divided into two groups according to AAA size (≤ 50 or > 50 mm) were compared with an age-matched group of 18 healthy subjects. Antioxidants (vitamins C and E, β-carotene, glutathione, thiols, and ubiquinone), trace elements (selenium, copper, zinc, and copper/zinc ratio) and markers of oxidative damage to lipids (lipid peroxides, antibodies against oxidized patients, and isoprostanes) were measured in each subject. The comparison of the three groups by ordinal logistic regression showed a significant decrease of the plasma levels of vitamin C (P = 0.011), α-tocopherol (P = 0.016) but not when corrected for cholesterol values, β-carotene (P = 0.0096), ubiquinone (P = 0.014), zinc (P = 0.0035), and of selenium (P = 0.0038), as AAA size increased. By contrast, specific markers of lipid peroxidation such as the Cu/Zn ratio (P = 0.046) and to a lesser extent isoprostanes (P = 0.052) increased.

CONCLUSION

The present study emphasizes the potential role of the oxidative stress in AAA disease and suggests that an antioxidant therapy could be of interest to delay AAA progression.

Role of uncoupled endothelial nitric oxide synthase in abdominal aortic aneurysm formation: treatment with folic acid

It has been shown that endothelial NO synthase (eNOS) uncoupling occurs in hypertension and atherosclerosis. However, its causal role in vascular pathogenesis has not been characterized previously. Here, we challenged eNOS preuncoupled hyperphenylalaninemia (hph)-1 mice (deficient in eNOS cofactor tetrahydrobiopterin biosynthetic enzyme GTPCHI) with angiotensin II (Ang II; 0.7 mg/kg per day, 14 days). Both wild-type and hph-1 groups developed hypertension similarly up to day 6 to 7. Thereafter, ≈14% of Ang II-infused (0.7 mg/kg per day) hph-1 mice (n=72) started to die suddenly of ruptured abdominal aortic aneurysm (AAA). Among the survivors, 65% developed AAA, resulting in a total morbidity rate of 79%. In contrast, none of the Ang II-infused wild-type mice died or developed AAA. Ang II progressively deteriorated eNOS uncoupling in hph-1 mice while augmenting tetrahydrobiopterin and nitric oxide (NO(·)) deficiencies. The abundance of the tetrahydrobiopterin salvage enzyme dihydrofolate reductase in the endothelium was decreased in hph-1 mice and further diminished by Ang II infusion. Intriguingly, restoration of dihydrofolate reductase expression by oral administration of folic acid or overexpression of dihydrofolate reductase completely prevented AAA formation in Ang II-infused hph-1 mice while attenuating progressive uncoupling of eNOS. Folic acid also attenuated vascular remodeling and inflammation characterized by medial elastin breakdown and augmented matrix metalloproteinase 2 activity and activation of matrix metalloproteinase 9, as well as macrophage infiltration. In conclusion, these data innovatively suggest a causal role of eNOS uncoupling/tetrahydrobiopterin deficiency in AAA formation. Therefore, oral folic acid administration, endothelium-targeted dihydrofolate reductase gene therapy, and perhaps other countermeasures directed against eNOS uncoupling could be used as new therapeutics for AAA.

Role of Oxidative Stress in the Pathogenesis of Abdominal Aortic Aneurysms

The role of inflammation in the pathogenesis of abdominal aortic aneurysms (AAA) is well established. The inflammatory process leads to protease-mediated degradation of the extracellular matrix and apoptosis of smooth muscle cells (SMC), which are the predominant matrix synthesizing cells of the vascular wall. These processes act in concert to progressively weaken the aortic wall, resulting in dilatation and aneurysm formation. Oxidative stress is invariably increased in, and contributes importantly to, the pathophysiology of inflammation. Moreover, reactive oxygen species (ROS) play a key role in regulation of matrix metalloproteinases and induction of SMC apoptosis. ROS may also contribute to the pathogenesis of hypertension, a risk factor for AAA. Emerging evidence suggests that ROS and reactive nitrogen species (RNS) are associated with AAA formation in animal models and in humans. Although experimental data are limited, several studies suggest that modulation of ROS production or activity may suppress AAA formation and improve experimental outcome in rodent models. Although a number of enzymes can produce injurious ROS in the vasculature, increasing evidence points toward a role for NADPH oxidase as a source of oxidative stress in the pathogenesis of AAA.

Vitamin E inhibits abdominal aortic aneurysm formation in angiotensin II-infused apolipoprotein E-deficient mice

BACKGROUND

Abdominal aortic aneurysms (AAAs) in humans are associated with locally increased oxidative stress and activity of NADPH oxidase. We investigated the hypothesis that vitamin E, an antioxidant with documented efficacy in mice, can attenuate AAA formation during angiotensin II (Ang II) infusion in apolipoprotein E-deficient mice.

METHODS AND RESULTS

Six-month-old male apolipoprotein E-deficient mice were infused with Ang II at 1000 ng/kg per minute for 4 weeks via osmotic minipumps while consuming either a regular diet or a diet enriched with vitamin E (2 IU/g of diet). After 4 weeks, abdominal aortic weight and maximal diameter were determined, and aortic tissues were sectioned and examined using biochemical and histological techniques. Vitamin E attenuated formation of AAA, decreasing maximal aortic diameter by 24% and abdominal aortic weight by 34% (P<0.05, respectively). Importantly, animals treated with vitamin E showed a 44% reduction in the combined end point of fatal+nonfatal aortic rupture (P<0.05). Vitamin E also decreased aortic 8-isoprostane content (a marker of oxidative stress) and reduced both aortic macrophage infiltration and osteopontin expression (P<0.05, respectively). Vitamin E treatment had no significant effect on the extent of aortic root atherosclerosis, activation of matrix metalloproteinases 2 or 9, serum lipid profile, or systolic blood pressure.

CONCLUSIONS

Vitamin E ameliorates AAAs and reduces the combined end point of fatal+nonfatal aortic rupture in this animal model. These findings are consistent with the concept that oxidative stress plays a pivotal role in Ang II-driven AAA formation in hyperlipidemic mice.

Vascular wall damage in rats induced by methidathion and ameliorating effect of vitamins E and C

We examined the effect of subacute methidathion (MD) administration on vascular wall damage and evaluated the ameliorating effects of combination of vitamins E and C against MD toxicity. The experimental groups were: rats treated with corn oil (control group), rats treated with 5 mg/kg MD (MD), and rats treated with 5 mg/kg body weight MD plus vitamin E and vitamin C (MD+Vit). The groups were given MD by gavage on 5 days a week for 4 weeks at a daily dose 5 mg/kg (MD and MD+Vit) using corn oil as the vehicle. Vitamins E and C were injected at doses of 50 mg/kg intramuscularly and 20 mg/kg intraperitoneally, respectively, after the treatment with MD in the MD+Vit group. The levels of malondialdehyde (MDA) were determined in the aortic tissue. Histopathological examination was examined in the thoracic aortic tissue. MDA levels were higher in the MD group than the control group and lower in the MD+Vit group than MD group. MD administration led to irregulation, prominent breaks, and fragmentation of the elastic fibers but decrease in the irregulation and fragmantation of the elastic fibers with the combination of vitamins E and C in MD-treated rats. In conclusion, it is likely that subacute MD administration caused vascular wall damage, and that treatment with a combination of vitamins E and C after the administration of MD can reduce vascular wall damage caused by MD.

Oxidative stress in human abdominal aortic aneurysms: a potential mediator of aneurysmal remodeling

Abdominal aortic aneurysm (AAA) is an inflammatory disorder characterized by localized connective tissue degradation and smooth muscle cell (SMC) apoptosis, leading to aortic dilatation and rupture. Reactive oxygen species are abundantly produced during inflammatory processes and can stimulate connective tissue-degrading proteases and apoptosis of SMCs. We hypothesized that reactive oxygen species are locally increased in AAA and lead to enhanced oxidative stress. In aortas from patients undergoing surgical repair, superoxide levels (measured by lucigenin-enhanced chemiluminescence) were 2.5-fold higher in the AAA segments compared with the adjacent nonaneurysmal aortic (NA) segments (6638+/-2164 versus 2675+/-1027 relative light units for 5 minutes per millimeter squared, respectively; n=7). Formation of thiobarbituric acid-reactive substances and conjugated dienes, 2 indices of lipid peroxidation, were increased 3-fold in AAA compared with NA segments. Immunostaining for nitrotyrosine was significantly greater in AAA tissue. Dihydroethidium staining indicated that increased superoxide in AAA segments was localized to infiltrating inflammatory cells and to SMCs. Expression of the NADPH oxidase subunits p47(phox) and p22(phox) and NAD(P)H oxidase activity were increased in AAA segments compared with NA segments. Thus, oxidative stress is markedly increased in AAA, in part through the activation of NAD(P)H oxidase, and may contribute to the disease pathogenesis.