Flow loading induces macrophage antioxidative gene expression in experimental aneurysms

A Multifaceted Approach to Abdominal Aortic Aneurysm

The underlying mechanisms of abdominal aortic aneurysms (AAAs) are not fully understood. Given the multifactorial nature of AAA development and progression, a comprehensive approach is essential. Throughout my academic career, I conducted various studies on AAA. To better understand this mechanism, I initially developed an elastase-infused rat AAA model and applied it to nanoparticle drug delivery systems. While open surgery has traditionally been the standard treatment for AAA, endovascular aneurysm repair (EVAR) has seen significant advancements over the past 25 years. However, insufficient evidence exists regarding this novel treatment, particularly in Japan. To address this issue, we analyzed extensive datasets on EVAR using various registries, including the Japanese Committee for Stent Graft Management. Furthermore, through medical-engineering collaboration, simulation methods were utilized to generate evidence addressing clinical questions encountered in practice.

Bridging the gap: Navigating the impact of dietary supplements on abdominal aortic aneurysm progression- A systematic review

BACKGROUND

Vitamins D, E, A, B, C, and Omega-3 play crucial roles in modulating inflammatory and oxidative stress pathways, both implicated in abdominal aortic aneurysm (AAA) development. Recent research has explored the potential impact of dietary supplements on AAA progression. The systematic review aims to assess interventional studies investigating the effects of various dietary supplements on the development and severity of abdominal aortic aneurysms.

METHOD

A systematic search using relevant keywords related to abdominal aortic aneurysm and dietary supplements was conducted across four databases (PubMed, Embase, Scopus, and Web of Science). Quality assessment for animal studies employed SYRCLE and the Cochrane Collaboration Risk of Bias Tool for randomized control trials. The study protocol is registered in PROSPERO under the registry code CRD42023455958.

RESULTS

Supplementation with Omega-3, Vitamins A, C, D, E, and the Vitamin B family exhibited positive effects in AAA progression. These supplements contributed to a reduction in AAA diameter, elastin degradation, inflammatory responses, and reactive oxygen species. Additional supplements such as Zinc, methionine, and phytoestrogen also played roles in mitigating AAA progression.

CONCLUSION

The findings of this study underscore the potential role of dietary supplements in the progression of AAA. Predominantly based on animal studies, the results indicate that these supplements can limit AAA progression, primarily evidenced by their ability to mitigate inflammatory processes and oxidative stress pathways.

Macrophages in cardiovascular diseases: molecular mechanisms and therapeutic targets

The immune response holds a pivotal role in cardiovascular disease development. As multifunctional cells of the innate immune system, macrophages play an essential role in initial inflammatory response that occurs following cardiovascular injury, thereby inducing subsequent damage while also facilitating recovery. Meanwhile, the diverse phenotypes and phenotypic alterations of macrophages strongly associate with distinct types and severity of cardiovascular diseases, including coronary heart disease, valvular disease, myocarditis, cardiomyopathy, heart failure, atherosclerosis and aneurysm, which underscores the importance of investigating macrophage regulatory mechanisms within the context of specific diseases. Besides, recent strides in single-cell sequencing technologies have revealed macrophage heterogeneity, cell-cell interactions, and downstream mechanisms of therapeutic targets at a higher resolution, which brings new perspectives into macrophage-mediated mechanisms and potential therapeutic targets in cardiovascular diseases. Remarkably, myocardial fibrosis, a prevalent characteristic in most cardiac diseases, remains a formidable clinical challenge, necessitating a profound investigation into the impact of macrophages on myocardial fibrosis within the context of cardiac diseases. In this review, we systematically summarize the diverse phenotypic and functional plasticity of macrophages in regulatory mechanisms of cardiovascular diseases and unprecedented insights introduced by single-cell sequencing technologies, with a focus on different causes and characteristics of diseases, especially the relationship between inflammation and fibrosis in cardiac diseases (myocardial infarction, pressure overload, myocarditis, dilated cardiomyopathy, diabetic cardiomyopathy and cardiac aging) and the relationship between inflammation and vascular injury in vascular diseases (atherosclerosis and aneurysm). Finally, we also highlight the preclinical/clinical macrophage targeting strategies and translational implications.

Mechano-chemo-biological Computational Models for Arteries in Health, Disease and Healing: From Tissue Remodelling to Drug-eluting Devices

This review aims to highlight urgent priorities for the computational biomechanics community in the framework of mechano-chemo-biological models. Recent approaches, promising directions and open challenges on the computational modelling of arterial tissues in health and disease are introduced and investigated, together with in silico approaches for the analysis of drug-eluting stents that promote pharmacological-induced healing. The paper addresses a number of chemo-biological phenomena that are generally neglected in biomechanical engineering models but are most likely instrumental for the onset and the progression of arterial diseases. An interdisciplinary effort is thus encouraged for providing the tools for an effective in silico insight into medical problems. An integrated mechano-chemo-biological perspective is believed to be a fundamental missing piece for crossing the bridge between computational engineering and life sciences, and for bringing computational biomechanics into medical research and clinical practice.

Effects of Exercise Training on Vascular Markers of Disease Progression in Patients with Small Abdominal Aortic Aneurysms

BACKGROUND

Currently, no medical therapy is effective in limiting progression of small abdominal aortic aneurysms (AAA; ≤5.5 cm). Previously, we have demonstrated safety and efficacy of exercise training in patients with AAA. However, the impact of exercise training on vascular markers of AAA progression, such as lipid accumulation product and matrix metalloproteinase 9 (MMP-9, linked to destruction of aortic matrix), is unknown. The aim of this study was to assess the impact of exercise training on AAA diameter, lipid accumulation product, MMP-9, and other risk markers of vascular disease.

METHODS

In this randomized trial, complete data of 96 patients (male: n = 87, female: n = 9; exercise training (exercise) n = 42, usual care n = 54) were studied. Changes in AAA diameter, exercise capacity, lipid accumulation product (men = [waist circumference 65] × fasting triglycerides; women = [waist circumference -58] × triglycerides) and MMP-9 were performed.

RESULTS

The exercise group demonstrated a significant increase in maximal exercise time and estimated metabolic equivalent of tasks. Lipid accumulation product decreased in exercise and increased in usual care (P < .001 between groups); MMP-9 remained statistically unchanged in exercise, but increased significantly in usual care (P = .005; between groups P = .094). In both groups, there was a significant increase in transverse diameter, but no difference between groups; neither group assignment nor level of fitness correlated with AAA enlargement. No adverse clinical events occurred.

CONCLUSIONS

This is the first study to demonstrate that in AAA, exercise beneficially modifies lipid accumulation product and MMP-9, both markers of vascular disease, without inducing aneurysmal growth beyond what is otherwise observed during usual care.

Therapeutic Potential of Heme Oxygenase-1 in Aneurysmal Diseases

Abdominal aortic aneurysm (AAA) and intracranial aneurysm (IA) are serious arterial diseases in the aorta and brain, respectively. AAA and IA are associated with old age in males and females, respectively, and if rupture occurs, they carry high morbidity and mortality. Aneurysmal subarachnoid hemorrhage (SAH) due to IA rupture has a high rate of complication and fatality. Despite these severe clinical outcomes, preventing or treating these devastating diseases remains an unmet medical need. Inflammation and oxidative stress are shared pathologies of these vascular diseases. Therefore, therapeutic strategies have focused on reducing inflammation and reactive oxygen species levels. Interestingly, in response to cellular stress, the inducible heme oxygenase-1 (HO-1) is highly upregulated and protects against tissue injury. HO-1 degrades the prooxidant heme and generates molecules with antioxidative and anti-inflammatory properties, resulting in decreased oxidative stress and inflammation. Therefore, increasing HO-1 activity is an attractive option for therapy. Several HO-1 inducers have been identified and tested in animal models for preventing or alleviating AAA, IA, and SAH. However, clinical trials have shown conflicting results. Further research and the development of highly selective HO-1 regulators may be needed to prevent the initiation and progression of AAA, IA, or SAH.

The Role of Sirtuin-1 in the Vasculature: Focus on Aortic Aneurysm

Sirtuin-1 (SirT1) is a nicotinamide adenine dinucleotide-dependent deacetylase and the best characterized member of the sirtuins family in mammalians. Sirtuin-1 shuttles between the cytoplasm and the nucleus, where it deacetylates histones and non-histone proteins involved in a plethora of cellular processes, including survival, growth, metabolism, senescence, and stress resistance. In this brief review, we summarize the current knowledge on the anti-oxidant, anti-inflammatory, anti-apoptotic, and anti-senescence effects of SirT1 with an emphasis on vascular diseases. Specifically, we describe recent research advances on SirT1-mediated molecular mechanisms in aortic aneurysm (AA), and how these processes relate to oxidant stress and the heme-oxygenase (HO) system. HO-1 and HO-2 catalyze the rate-limiting step of cellular heme degradation and, similar to SirT1, HO-1 exerts beneficial effects in the vasculature through the activation of anti-oxidant, anti-inflammatory, anti-apoptotic, and anti-proliferative signaling pathways. SirT1 and HO-1 are part of an integrated system for cellular stress tolerance, and may positively interact to regulate vascular function. We further discuss sex differences in HO-1 and SirT1 activity or expression, and the potential interactions between the two proteins, in relation to the progression and severity of AA, as well as the ongoing efforts for translational applications of SirT1 activation and HO-1 induction in the treatment of cardiovascular diseases including AA.

Effectiveness and safety of structured exercise vs. no exercise for asymptomatic aortic aneurysm: systematic review and meta-analysis

We conducted a systematic review to compare the effectiveness and safety of exercise versus no exercise for patients with asymptomatic aortic aneurysm. We followed the guidelines set out in the Cochrane systematic review handbook. We searched Medline, Embase, CENTRAL, LILACS, PeDRO, CINAHL, clinicaltrials.gov, ICTRP, and OpenGrey using the MeSH terms “aortic aneurysm” and “exercise”. 1189 references were identified. Five clinical trials were included. No exercise-related deaths or aortic ruptures occurred in these trials. Exercise did not reduce the aneurysm expansion rate at 12 weeks to 12 months (mean difference [MD], −0.05; 95% confidence interval [CI], −0.13 to 0.03). Six weeks of preoperative exercise reduced severe renal and cardiac complications (risk ratio, 0.54; 95% CI, 0.31–0.93) and the length of intensive care unit stay (MD, −1.00; 95% CI, −1.26 to −0.74). Preoperative and postoperative forward walking reduced the length of hospital stay (MD, −0.69; 95% CI, −1.24 to −0.14). The evidence was graded as ‘very low’ level.

Comprehensive Cardiac Rehabilitation as a Therapeutic Strategy for Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAA) are referred to as “time bombs”. The only way to prevent AAA rupture is elective repair beforehand using surgical replacement or an endovascular procedure. Non-surgical strategies to prevent AAA expansion are under intense investigation. At each AAA stage, that is, occurrence, expansion, and rupture, the mechanisms and risk factors are different, as discussed in this review. Based on the mechanism and risk factors for AAA expansion, the most effective strategy against AAA expansion need to be identified, but so far none has. Exercise is known to be essential for preventing atherosclerosis related to the coexistence of AAA and CAD, but some doctors are hesitant to prescribe exercise programs to AAA patients given that BP elevation during exercise can cause AAA expansion or rupture. In our retrospective study and prospective study on the safety and effectiveness of exercise for AAA patients, the protective role of mild-moderate exercise against expansion of small AAA was clearly shown. The stability of AAA on exercise might be related to reduced inflammatory activity in the aortic wall, stabilized elevation in BP during exercise, increased aortic blood flow, upregulation of transforming growth factor-β1, moderated BMI and/or fat, or improved endothelial function. Until a revolutionary drug emerges that can regress AAA, cardiac rehabilitation remains the best strategy for preventing AAA expansion and rupture.

Role of Vascular Smooth Muscle Cell Phenotypic Switching and Calcification in Aortic Aneurysm Formation

Aortic aneurysm is a vascular disease whereby the ECM (extracellular matrix) of a blood vessel degenerates, leading to dilation and eventually vessel wall rupture. Recently, it was shown that calcification of the vessel wall is involved in both the initiation and progression of aneurysms. Changes in aortic wall structure that lead to aneurysm formation and vascular calcification are actively mediated by vascular smooth muscle cells. Vascular smooth muscle cells in a healthy vessel wall are termed contractile as they maintain vascular tone and remain quiescent. However, in pathological conditions they can dedifferentiate into a synthetic phenotype, whereby they secrete extracellular vesicles, proliferate, and migrate to repair injury. This process is called phenotypic switching and is often the first step in vascular pathology. Additionally, healthy vascular smooth muscle cells synthesize VKDPs (vitamin K-dependent proteins), which are involved in inhibition of vascular calcification. The metabolism of these proteins is known to be disrupted in vascular pathologies. In this review, we summarize the current literature on vascular smooth muscle cell phenotypic switching and vascular calcification in relation to aneurysm. Moreover, we address the role of vitamin K and VKDPs that are involved in vascular calcification and aneurysm. Visual Overview- An online visual overview is available for this article.

Role of Noncoding RNAs in the Pathogenesis of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a local dilatation of the abdominal aortic vessel wall and is among the most challenging cardiovascular diseases as without urgent surgical intervention, ruptured AAA has a mortality rate of >80%. Most patients present acutely after aneurysm rupture or dissection from a previously asymptomatic condition and are managed by either surgery or endovascular repair. Patients usually are old and have other concurrent diseases and conditions, such as diabetes mellitus, obesity, and hypercholesterolemia making surgical intervention more difficult. Collectively, these issues have driven the search for alternative methods of diagnosing, monitoring, and treating AAA using therapeutics and less invasive approaches. Noncoding RNAs-short noncoding RNAs (microRNAs) and long-noncoding RNAs-are emerging as new fundamental regulators of gene expression. Researchers and clinicians are aiming at targeting these microRNAs and long noncoding RNAs and exploit their potential as clinical biomarkers and new therapeutic targets for AAAs. While the role of miRNAs in AAA is established, studies on long-noncoding RNAs are only beginning to emerge, suggesting their important yet unexplored role in vascular physiology and disease. Here, we review the role of noncoding RNAs and their target genes focusing on their role in AAA. We also discuss the animal models used for mechanistic understanding of AAA. Furthermore, we discuss the potential role of microRNAs and long noncoding RNAs as clinical biomarkers and therapeutics.

Potential Medication Treatment According to Pathological Mechanisms in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a vascular disease with high mortality. Because of the lack of effective medications to stop or reverse the progression of AAA, surgical operation has become the most predominant recommendation of treatment for patients. There are many potential mechanisms, including inflammation, smooth muscle cell apoptosis, extracellular matrix degradation, oxidative stress, and so on, involving in AAA pathogenesis. According to those mechanisms, some potential therapeutic drugs have been proposed and tested in animal models and even in clinical trials. This review focuses on recent advances in both pathogenic mechanisms and potential pharmacologic therapies of AAA.

Tamsulosin attenuates abdominal aortic aneurysm growth

BACKGROUND

Tamsulosin, an α1A-adrenergic receptor inhibitor, is prescribed to treat benign prostatic hyperplasia in men >60 years of age, the same demographic most susceptible to abdominal aortic aneurysm. The goal of this study was to investigate the effect of tamsulosin on abdominal aortic aneurysm pathogenesis.

METHODS

Abdominal aortic aneurysms were induced in WT C57BL/6 male mice (n = 9-18/group), using an established topical elastase abdominal aortic aneurysm model. Osmotic pumps were implanted in mice 5 days before operation to create the model, administering either low dose (0.125 µg/day tamsulosin), high dose (0.250µg/day tamsulosin), or vehicle treatments with and without topical application of elastase. Blood pressures were measured preoperatively and on postoperative days 0, 3, 7, and 14. On postoperative day 14, aortic diameter was measured before harvest. Sample aortas were prepared for histology and cytokine analysis.

RESULTS

Measurements of systolic blood pressure did not differ between groups. Mice treated with the low dose of tamsulosin and with the high dose of tamsulosin showed decreased aortic diameter compared with vehicle-treated control (93% ± 24 versus 94% ± 30 versus 132% ± 24, respectively; P = .0003, P = .0003). Cytokine analysis demonstrated downregulation of pro-inflammatory cytokines in both treatment groups compared with the control (P < .05). Histology exhibited preservation of elastin in both low- and high-dose tamsulosin-treated groups (P = .0041 and P = .0018, respectively).

CONCLUSION

Tamsulosin attenuates abdominal aortic aneurysm formation with increased preservation of elastin and decreased production of pro-inflammatory cytokines. Further studies are necessary to elucidate the mechanism by which tamsulosin attenuates abdominal aortic aneurysm pathogenesis.

Heme oxygenase-1 deficiency exacerbates angiotensin II-induced aortic aneurysm in mice

Abdominal aortic aneurysm (AAA) is a chronic but often fatal disease in elderly population. Heme oxygenase-1 (HO-1) is a stress response protein with antioxidative and anti-inflammatory properties. HO-1 has been shown to protect against atherogenesis and arterial intimal thickening. Emerging evidences suggest that AAA and arterial occlusive disease have distinct pathogenic mechanisms. Thus, in this study we investigated the role of HO-1 in angiotensin II-induced AAA formation in HO-1^+/+apoE^−/− and HO-1^−/−apoE^−/− mice. We found that complete loss of HO-1 increased AAA incidence and rupture rate, and drastically increased aneurysmal area and severity, accompanied with severe elastin degradation and medial degeneration. Interestingly, we often observed not only AAA but also thoracic aortic aneurysm in HO-1^−/−apoE^−/− mice. Furthermore, reactive oxygen species levels, vascular smooth muscle cell (VSMC) loss, macrophage infiltration, matrix metalloproteinase (MMP) activity were markedly enhanced in the aneurysmal aortic wall in HO-1^−/−apoE^−/− mice. In addition, HO-1^−/−apoE^−/− VSMCs were more susceptible to oxidant-induced cell death and macrophages from HO-1^−/−apoE^−/− mice had aggravated responses to angiotensin II with substantial increases in inflammatory cytokine productions and MMP9 activity. Taken together, our results demonstrate the essential roles of HO-1 in suppressing the pathogenesis of AAA. Targeting HO-1 might be a promising therapeutic strategy for AAA.

Erythrocytes, leukocytes and platelets as a source of oxidative stress in chronic vascular diseases: Detoxifying mechanisms and potential therapeutic options

Oxidative stress is involved in the chronic pathological vascular remodelling of both abdominal aortic aneurysm and occlusive atherosclerosis. Red blood cells (RBCs), leukocytes and platelets present in both, aneurysmal intraluminal thrombus and intraplaque haemorraghes, could be involved in the redox imbalance inside diseased arterial tissues. RBCs haemolysis may release the pro-oxidant haemoglobin (Hb), which transfers heme to tissue and low-density lipoproteins. Heme-iron potentiates molecular, cell and tissue toxicity mediated by leukocytes and other sources of reactive oxygen species (ROS). Polymorphonuclear neutrophils release myeloperoxidase and, along with activated platelets, produce superoxide mediated by NADPH oxidase, causing oxidative damage. In response to this pro-oxidant milieu, several anti-oxidant molecules of plasma or cell origin can prevent ROS production. Free Hb binds to haptoglobin (Hp) and once Hp-Hb complex is endocytosed by CD163, liberated heme is converted into less toxic compounds by heme oxygenase-1. Iron homeostasis is mainly regulated by transferrin, which transports ferric ions to other cells. Transferrin-bound iron is internalised via endocytosis mediated by transferrin receptor. Once inside the cell, iron is mainly stored by ferritin. Other non hemo-iron related antioxidant enzymes (e.g. superoxide dismutase, catalase, thioredoxin and peroxiredoxin) are also involved in redox modulation in vascular remodelling. Oxidative stress is a main determinant of chronic pathological remodelling of the arterial wall, partially linked to the presence of RBCs, leukocytes, platelets and oxidised fibrin within tissue and to the imbalance between pro-/anti-oxidant molecules. Understanding the complex mechanisms underlying redox imbalance could help to define novel potential targets to decrease atherothrombotic risk.

Reactive oxygen species: key regulators in vascular health and diseases

ROS are a group of small reactive molecules that play critical roles in the regulation of various cell functions and biological processes. In the vascular system, physiological levels of ROS are essential for normal vascular functions including endothelial homeostasis and smooth muscle cell contraction. In contrast, uncontrolled overproduction of ROS resulting from an imbalance of ROS generation and elimination leads to the development of vascular diseases. Excessive ROS cause vascular cell damage, the recruitment of inflammatory cells, lipid peroxidation, activation of metalloproteinases and deposition of extracellular matrix, collectively leading to vascular remodelling. Evidence from a large number of studies has revealed that ROS and oxidative stress are involved in the initiation and progression of numerous vascular diseases including hypertension, atherosclerosis, restenosis and abdominal aortic aneurysm. Furthermore, considerable research has been implemented to explore antioxidants that can reduce ROS production and oxidative stress in order to ameliorate vascular diseases. In this review, we will discuss the nature and sources of ROS, their roles in vascular homeostasis and specific vascular diseases and various antioxidants as well as some of the pharmacological agents that are capable of reducing ROS and oxidative stress. The aim of this review is to provide information for developing promising clinical strategies targeting ROS to decrease cardiovascular risks.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

A FSI computational framework for vascular physiopathology: A novel flow-tissue multiscale strategy

A novel fluid-structure computational framework for vascular applications is herein presented. It is developed by combining the double multi-scale nature of vascular physiopathology in terms of both tissue properties and blood flow. Addressing arterial tissues, they are modelled via a nonlinear multiscale constitutive rationale, based only on parameters having a clear histological and biochemical meaning. Moreover, blood flow is described by coupling a three-dimensional fluid domain (undergoing physiological inflow conditions) with a zero-dimensional model, which allows to reproduce the influence of the downstream vasculature, furnishing a realistic description of the outflow proximal pressure. The fluid-structure interaction is managed through an explicit time-marching approach, able to accurately describe tissue nonlinearities within each computational step for the fluid problem. A case study associated to a patient-specific aortic abdominal aneurysmatic geometry is numerically investigated, highlighting advantages gained from the proposed multiscale strategy, as well as showing soundness and effectiveness of the established framework for assessing useful clinical quantities and risk indexes.

Development of Vascular Biology over the past 10 Years: Heme Oxygenase-1 in Cardiovascular Homeostasis

The study of vascular biology has provided strong evidence for the role that free radical attack plays in the pathogenesis of cardiovascular diseases. The endothelial cell (EC) dysfunction that results from exposure to oxidative stresses, such as oxidized LDL, influences vascular cell gene expression, promoting smooth muscle cell (SMC) mitogenesis and apoptosis. These factors also play an important role in atherogenesis, which is attenuated by antioxidants. Thus, antioxidants are important to understanding the pathophysiology of cardiovascular diseases and to constructing an effective treatment strategy for these patients. Over the last decade, there has been a tremendous interest in the biology of heme oxygenase-1 (HO-1), which exhibits antioxidant effects in various forms of tissue injury. Moreover, the reaction is also the major source of carbon dioxide (CO) in the body, which is a physiologically important gaseous vasodilator that inhibits SMC proliferation. Thus, HO-1–derived products provide various mechanisms to maintain cardiovascular homeostasis. We review recent work on the cellular and molecular biological aspects of the HO/CO system in vascular pathophysiology.

Increased Oxidative Stress and Xanthine Oxidase Activity in Human Ruptured Cerebral Aneurysms

Recent studies have suggested that oxidative stress may be involved in the development of arterial aneurysms. Xanthine oxidase is implicated in the generation of reactive oxygen species under pathological conditions in the cardiovascular system, and increased xanthine oxidase activity has been reported in human aortic aneurysms. We, therefore, studied the changes of xanthine oxidase activity and oxidative stress in human ruptured cerebral aneurysms. Six cerebral aneurysmal samples were obtained during surgery. Normal arteries of the similar size (one superficial temporal artery, four uterine arteries and three right gastroepiploic arteries) were used as controls. The xanthine oxidase activity was measured with a commercial assay kit, and its expression was localized by immunohistochemistry. The xanthine oxidase activity was significantly increased in aneurysms by 4.1 fold (P<0.05) compared to control arteries. This was accompanied by an elevated malondialdehyde (MDA) level (8.3±5.1 versus 2.9±0.7 nmol/g protein, mean ±SD, P<0.05), a marker of oxidative stress. Immunohistochemistry established that xanthine oxidase was mainly expressed in infiltrating inflammatory cells. Our study indicates that xanthine oxidase may have an important role in the increased oxidative stress in ruptured cerebral aneurysms. Further studies are needed to clarify the role of XO-derived reactive oxygen species in the development and rupture of cerebral aneurysms.

Oxidative stress and abdominal aortic aneurysm: potential treatment targets

Abdominal aortic aneurysm (AAA) is a significant cause of mortality in older adults. A key mechanism implicated in AAA pathogenesis is inflammation and the associated production of reactive oxygen species (ROS) and oxidative stress. These have been suggested to promote degradation of the extracellular matrix (ECM) and vascular smooth muscle apoptosis. Experimental and human association studies suggest that ROS can be favourably modified to limit AAA formation and progression. In the present review, we discuss mechanisms potentially linking ROS to AAA pathogenesis and highlight potential treatment strategies targeting ROS. Currently, none of these strategies has been shown to be effective in clinical practice.

Heme Oxygenase-1 Expression Affects Murine Abdominal Aortic Aneurysm Progression

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, is a cytoprotective enzyme upregulated in the vasculature by increased flow and inflammatory stimuli. Human genetic data suggest that a diminished HO-1 expression may predispose one to abdominal aortic aneurysm (AAA) development. In addition, heme is known to strongly induce HO-1 expression. Utilizing the porcine pancreatic elastase (PPE) model of AAA induction in HO-1 heterozygous (HO-1^+/-, HO-1 Het) mice, we found that a deficiency in HO-1 leads to augmented AAA development. Peritoneal macrophages from HO-1^+/- mice showed increased gene expression of pro-inflammatory cytokines, including MCP-1, TNF-alpha, IL-1-beta, and IL-6, but decreased expression of anti-inflammatory cytokines IL-10 and TGF-beta. Furthermore, treatment with heme returned AAA progression in HO-1 Het mice to a wild-type profile. Using a second murine AAA model (Ang II-ApoE^-/-), we showed that low doses of the HMG-CoA reductase inhibitor rosuvastatin can induce HO-1 expression in aortic tissue and suppress AAA progression in the absence of lipid lowering. Our results support those studies that suggest that pleiotropic statin effects might be beneficial in AAA, possibly through the upregulation of HO-1. Specific targeted therapies designed to induce HO-1 could become an adjunctive therapeutic strategy for the prevention of AAA disease.

Diabetic Cardiovascular Disease Induced by Oxidative Stress

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality among patients with diabetes mellitus (DM). DM can lead to multiple cardiovascular complications, including coronary artery disease (CAD), cardiac hypertrophy, and heart failure (HF). HF represents one of the most common causes of death in patients with DM and results from DM-induced CAD and diabetic cardiomyopathy. Oxidative stress is closely associated with the pathogenesis of DM and results from overproduction of reactive oxygen species (ROS). ROS overproduction is associated with hyperglycemia and metabolic disorders, such as impaired antioxidant function in conjunction with impaired antioxidant activity. Long-term exposure to oxidative stress in DM induces chronic inflammation and fibrosis in a range of tissues, leading to formation and progression of disease states in these tissues. Indeed, markers for oxidative stress are overexpressed in patients with DM, suggesting that increased ROS may be primarily responsible for the development of diabetic complications. Therefore, an understanding of the pathophysiological mechanisms mediated by oxidative stress is crucial to the prevention and treatment of diabetes-induced CVD. The current review focuses on the relationship between diabetes-induced CVD and oxidative stress, while highlighting the latest insights into this relationship from findings on diabetic heart and vascular disease.

Association of Intraluminal Thrombus, Hemodynamic Forces, and Abdominal Aortic Aneurysm Expansion Using Longitudinal CT Images

While hemodynamic forces and intraluminal thrombus (ILT) are believed to play important roles on abdominal aortic aneurysm (AAA), it has been suggested that hemodynamic forces and ILT also interact with each other, making it a complex problem. There is, however, a pressing need to understand relationships among three factors: hemodynamics, ILT accumulation, and AAA expansion for AAA prognosis. Hence this study used longitudinal computer tomography scans from 14 patients and analyzed the relationship between them. Hemodynamic forces, represented by wall shear stress (WSS), were obtained from computational fluid dynamics; ILT accumulation was described by ILT thickness distribution changes between consecutives scans, and ILT accumulation and AAA expansion rates were estimated from changes in ILT and AAA volume. Results showed that, while low WSS was observed at regions where ILT accumulated, the rate at which ILT accumulated occurred at the same rate as the aneurysm expansion. Comparison between AAAs with and without thrombus showed that aneurysm with ILT recorded lower values of WSS and higher values of AAA expansion than those without thrombus. Findings suggest that low WSS may promote ILT accumulation and submit the idea that by increasing WSS levels ILT accumulation may be prevented.

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.

Patient recruitment and experiences in a randomised trial of supervised exercise training for individuals with abdominal aortic aneurysm

We sought to describe patient recruitment and experiences in a randomised controlled trial of a 12-week (thrice weekly) supervised exercise program for patients with small abdominal aortic aneurysm (AAA). Potential patients were identified via AAA surveillance lists and vascular clinics and invited to participate in the study. Upon completion of baseline assessments, patients were randomly allocated 1:1 to exercise or usual care. Patients completing the exercise arm were invited to attend a focus group session to explore experiences of diagnosis, management of condition, trial recruitment, and expectations and experiences of the exercise program. Between January 2010 and September 2011, 545 patients were identified. The response rate to postal invitation was 81.7% (445/545), with 108 patients responding as "interested." Only 28 of these patients were eligible and recruited (46.7% of recruitment target), yielding an overall recruitment rate of 5.1%. However, the estimated recruitment rate among eligible patients was 23.7%. Twenty-five patients (89.3%) completed the study, and compliance to the exercise program was 94%. Participants attending the focus group session indicated that the exercise program was manageable, beneficial, and enjoyable. The feasibility of supervised exercise training in individuals with small AAA remains unclear. Our study revealed a poorer than expected recruitment rate, but good compliance to, and feedback for, the exercise intervention. We present potential explanations for these findings and suggestions for future trials involving similar populations.

Segmental aortic stiffening contributes to experimental abdominal aortic aneurysm development

BACKGROUND

Stiffening of the aortic wall is a phenomenon consistently observed in age and in abdominal aortic aneurysm (AAA). However, its role in AAA pathophysiology is largely undefined.

METHODS AND RESULTS

Using an established murine elastase-induced AAA model, we demonstrate that segmental aortic stiffening precedes aneurysm growth. Finite-element analysis reveals that early stiffening of the aneurysm-prone aortic segment leads to axial (longitudinal) wall stress generated by cyclic (systolic) tethering of adjacent, more compliant wall segments. Interventional stiffening of AAA-adjacent aortic segments (via external application of surgical adhesive) significantly reduces aneurysm growth. These changes correlate with the reduced segmental stiffness of the AAA-prone aorta (attributable to equalized stiffness in adjacent segments), reduced axial wall stress, decreased production of reactive oxygen species, attenuated elastin breakdown, and decreased expression of inflammatory cytokines and macrophage infiltration, and attenuated apoptosis within the aortic wall, as well. Cyclic pressurization of segmentally stiffened aortic segments ex vivo increases the expression of genes related to inflammation and extracellular matrix remodeling. Finally, human ultrasound studies reveal that aging, a significant AAA risk factor, is accompanied by segmental infrarenal aortic stiffening.

CONCLUSIONS

The present study introduces the novel concept of segmental aortic stiffening as an early pathomechanism generating aortic wall stress and triggering aneurysmal growth, thereby delineating potential underlying molecular mechanisms and therapeutic targets. In addition, monitoring segmental aortic stiffening may aid the identification of patients at risk for AAA.

High-fat diet- and angiotensin II-induced aneurysm concurrently elicits splenic hypertrophy

BACKGROUND

Angiotensin II (Ang II) and high-fat diet are implicated in causing pathological changes in the vascular endothelium, brain, kidney and liver. The association of aneurysm leading to histopathological changes in the splenic compartment remains elusive. Further, the salubrious credentials of antioxidants, especially α-tocopherol and β-carotene in the resolution of splenic pathology have not been investigated.

METHODS

Four-month-old Apoe(-/-) mice were used in the induction of aneurysm by infusing Ang II, and subsequently were orally administered with α-tocopherol and β-carotene-enriched diet for 60 days.

RESULTS

We observed splenomegaly in Ang II-infused aneurysm and high-fat diet-supplemented mice as compared to normal mice. These observations were further confirmed through histopathological investigations, demonstrating splenic follicular hypertrophy. We observed a remarkable decrease in the size of spleen in α-tocopherol and β-carotene-treated Apoe(-/-) mice as compared with Ang II-treated animals. Furthermore, no marked changes in the histopathological splenic sections were seen in the β-carotene-treated group. However, hyperplasia and proliferation of immature lymphocytes in the follicles were observed in the α-tocopherol-treated animals. We found that CD4+ T-cell levels were increased in the high-fat diet group relative to the control group and were decreased in the β-carotene-treated animals.

CONCLUSIONS

Our study provides evidence that Ang II infusion and high-fat supplementation induces abdominal aortic aneurysm that has pathological implications to the spleen. The use of β-carotene but not α-tocopherol as an antioxidant markedly ameliorates the pathological changes in spleen.

Hemodynamic regulation of reactive oxygen species: implications for vascular diseases

SIGNIFICANCE

Arterial blood vessels functionally and structurally adapt to altering hemodynamic forces in order to accommodate changing needs and to provide stress homeostasis. This ability is achieved at the cellular level by converting mechanical stimulation into biochemical signals (i.e., mechanotransduction). Physiological mechanical stress helps maintain vascular structure and function, whereas pathologic or aberrant stress may impair cellular mechano-signaling, and initiate or augment cellular processes that drive disease.

RECENT ADVANCES

Reactive oxygen species (ROS) may represent an intriguing class of mechanically regulated second messengers. Chronically enhanced ROS generation may be induced by adverse mechanical stresses, and is associated with a multitude of vascular diseases. Although a causal relationship has clearly been demonstrated in large numbers of animal studies, an effective ROS-modulating therapy still remains to be established by clinical studies.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This review article focuses on the role of various mechanical forces (in the form of laminar shear stress, oscillatory shear stress, or cyclic stretch) as modulators of ROS-driven signaling, and their subsequent effects on vascular biology and homeostasis, as well as on specific diseases such as arteriosclerosis, hypertension, and abdominal aortic aneurysms. Specifically, it highlights the significance of the various NADPH oxidase (NOX) isoforms as critical ROS generators in the vasculature. Directed targeting of defined components in the complex network of ROS (mechano-)signaling may represent a key for successful translation of experimental findings into clinical practice.

Smooth muscle cells from abdominal aortic aneurysms are unique and can independently and synergistically degrade insoluble elastin

BACKGROUND

The purpose of this study was to further elucidate the role of the vascular smooth muscle cells (SMCs) in abdominal aortic aneurysm (AAA) disease. We hypothesized that that AAA SMCs are unique and actively participate in the process of degrading the aortic matrix.

METHODS

Whole-genome expression profiles of SMCs from AAAs, nondilated abdominal aorta (NAA), and carotid endarterectomy (CEA) were compared. We quantified elastolytic activity by culturing SMCs in [(3)H]elastin-coated plates and measuring solubilized tritium in the media after 7 days. Matrix metalloproteinase (MMP)-2 and MMP-9 production was assessed using real-time polymerase chain reaction, zymography, and Western blotting.

RESULTS

Each SMC type exhibited a unique gene expression pattern. AAA SMCs had greater elastolytic activity than NAA-SMCs (+68%; P < .001) and CEA-SMCs (+45%; P < .001). Zymography showed an increase of active MMP-2 (62 kD) in media from AAA SMCs. AAA SMCs demonstrated twofold greater expression of MMP-2 messenger (m)RNA (P < .05) and 7.3-fold greater MMP-9 expression (P < .01) than NAA-SMCs. Culture with U937 monocytes caused a synergistic increase of elastolysis by AAA SMCs (41%; P < .001) but not NAA-SMCs or CEA-SMCs (P = .99). Coculture with U937 caused a large increase in MMP-9 mRNA in AAA-SMCs and NAA-SMCs (P < .001). MMP-2 mRNA expression was not affected. Western blots of culture media showed a fourfold increase of MMP-9 (92 kD) protein only in AAA-SMCs/U937 but not in NAA-SMCs/U937 (P < .001) and a large increase in active-MMP2 (62 kD), which was less apparent in NAA-SMCs/U937 media (P < .01).

CONCLUSIONS

AAA-SMCs have a unique gene expression profile and a proelastolytic phenotype that is augmented by macrophages. This may occur by a failure of post-transcriptional control of MMP-9 synthesis.

β-Carotene Attenuates Angiotensin II-Induced Aortic Aneurysm by Alleviating Macrophage Recruitment in Apoe(-/-) Mice

Abdominal aortic aneurysm (AAA) is a common chronic degenerative disease characterized by progressive aortic dilation and rupture. The mechanisms underlying the role of α-tocopherol and β-carotene on AAA have not been comprehensively assessed. We investigated if α-tocopherol and β-carotene supplementation could attenuate AAA, and studied the underlying mechanisms utilized by the antioxidants to alleviate AAA. Four-months-old Apoe^−/− mice were used in the induction of aneurysm by infusion of angiotensin II (Ang II), and were orally administered with α-tocopherol and β-carotene enriched diet for 60 days. Significant increase of LDL, cholesterol, triglycerides and circulating inflammatory cells was observed in the Ang II-treated animals, and gene expression studies showed that ICAM-1, VCAM-1, MCP-1, M-CSF, MMP-2, MMP-9 and MMP-12 were upregulated in the aorta of aneurysm-induced mice. Extensive plaques, aneurysm and diffusion of inflammatory cells into the tunica intima were also noticed. The size of aorta was significantly (P = 0.0002) increased (2.24±0.20 mm) in the aneurysm-induced animals as compared to control mice (1.17±0.06 mm). Interestingly, β-carotene dramatically controlled the diffusion of macrophages into the aortic tunica intima, and circulation. It also dissolved the formation of atheromatous plaque. Further, β-carotene significantly decreased the aortic diameter (1.33±0.12 mm) in the aneurysm-induced mice (β-carotene, P = 0.0002). It also downregulated ICAM-1, VCAM-1, MCP-1, M-CSF, MMP-2, MMP-9, MMP-12, PPAR-α and PPAR-γ following treatment. Hence, dietary supplementation of β-carotene may have a protective function against Ang II-induced AAA by ameliorating macrophage recruitment in Apoe^−/− mice.

Efficacy and mechanism of angiotensin II receptor blocker treatment in experimental abdominal aortic aneurysms

Background

Despite the importance of the renin-angiotensin (Ang) system in abdominal aortic aneurysm (AAA) pathogenesis, strategies targeting this system to prevent clinical aneurysm progression remain controversial and unproven. We compared the relative efficacy of two Ang II type 1 receptor blockers, telmisartan and irbesartan, in limiting experimental AAAs in distinct mouse models of aneurysm disease.

Methodology/Principal Findings

AAAs were induced using either 1) Ang II subcutaneous infusion (1000 ng/kg/min) for 28 days in male ApoE^−/− mice, or 2) transient intra-aortic porcine pancreatic elastase infusion in male C57BL/6 mice. One week prior to AAA creation, mice started to daily receive irbesartan (50 mg/kg), telmisartan (10 mg/kg), fluvastatin (40 mg/kg), bosentan (100 mg/kg), doxycycline (100 mg/kg) or vehicle alone. Efficacy was determined via serial in vivo aortic diameter measurements, histopathology and gene expression analysis at sacrifice. Aortic aneurysms developed in 67% of Ang II-infused ApoE^−/− mice fed with standard chow and water alone (n = 15), and 40% died of rupture. Strikingly, no telmisartan-treated mouse developed an AAA (n = 14). Both telmisartan and irbesartan limited aneurysm enlargement, medial elastolysis, smooth muscle attenuation, macrophage infiltration, adventitial neocapillary formation, and the expression of proteinases and proinflammatory mediators. Doxycycline, fluvastatin and bosentan did not influence aneurysm progression. Telmisartan was also highly effective in intra-aortic porcine pancreatic elastase infusion-induced AAAs, a second AAA model that did not require exogenous Ang II infusion.

Conclusion/Significance

Telmisartan suppresses experimental aneurysms in a model-independent manner and may prove valuable in limiting clinical disease progression.

Recent advances in pharmacotherapy development for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease causing segmental expansion and rupture of the aorta with a high mortality rate. The lack of nonsurgical treatment represents a large and unmet need in terms of pharmacotherapy. Advances in AAA research revealed that activation of inflammatory signaling pathways through proinflammatory mediators shifts the balance of extracellular matrix (ECM) metabolism toward tissue degradation. This idea is supported by experimental evidence in animal models that pharmacologic intervention at each pathological step can prevent AAA development. Previously, we identified c-Jun N-terminal kinase (JNK), a pro-inflammatory signaling molecule, as a therapeutic target for AAA. Abnormal activation of JNK in AAA tissue regulates multiple pathological processes in a coordinated manner. Pharmacologic inhibition of JNK tips the ECM balance back towards repair rather than degradation. Interventions targeting signaling molecules such as JNK in order to manipulate multiple pathological processes may be an ideal therapeutic strategy for AAA. Furthermore, the development of biomarkers as well as appropriate drug delivery systems is essential to produce clinically practical pharmacotherapy for AAA.

Endurance exercise training in patients with small abdominal aortic aneurysm: a randomized controlled pilot study

OBJECTIVE

To investigate the feasibility of endurance exercise training in patients with small abdominal aortic aneurysm (AAA), and to obtain preliminary data of its impact on important health outcomes.

DESIGN

Randomized controlled pilot study.

SETTING

University rehabilitation facility.

PARTICIPANTS

Patients with small AAA (N=28; mean age ± SD, 72±7 y).

INTERVENTION

Participants were randomized to a 12-week program of moderate-intensity endurance exercise or standard care control (encouragement to exercise only).

MAIN OUTCOME MEASURES

Safety was assessed in terms of the frequency of adverse events and changes in maximum AAA diameter. Outcomes were assessed at baseline and 12 weeks including cardiopulmonary fitness (ventilatory threshold), health-related quality of life (Medical Outcomes Study 36-Item Short-Form Health Survey [version 2]), and markers of vascular risk (eg, blood pressure and high-sensitivity C-reactive protein).

RESULTS

Of 545 patients contacted, 28 (5%) entered the trial. There were 3 (11%) dropouts. Adherence to the exercise program was 94%. There were no paradoxical increases in AAA size or adverse clinical events. Ventilatory threshold increased in the exercise group, but not the control group (adjusted mean difference, 2.5 mL·kg(-1)·min(-1); 95% confidence interval, 0.5-4.5; d=.82). Systolic blood pressure and high-sensitivity C-reactive protein decreased in the exercise group compared with the control group (d=.34 and d=.58, respectively). There were no substantial changes in anthropometric variables or quality of life.

CONCLUSIONS

Despite a low recruitment rate, the findings suggest that moderate-intensity endurance exercise training is feasible in patients with small AAA, and can evoke improvements in important health outcomes.

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.

Proteomic Analysis of Polymorphonuclear Neutrophils Identifies Catalase as a Novel Biomarker of Abdominal Aortic Aneurysm: Potential Implication of Oxidative Stress in Abdominal Aortic Aneurysm Progression

Objective—

Polymorphonuclear neutrophils (PMNs) play a main role in abdominal aortic aneurysm (AAA) progression. We have analyzed circulating PMNs isolated from AAA patients and controls by a proteomic approach to identify proteins potentially involved in AAA pathogenesis.

Methods and Results—

PMNs from 8 AAA patients (4 large AAA >5 cm and 4 small AAA 3–5 cm) and 4 controls were analyzed by 2D differential in-gel electrophoresis. Among differentially expressed spots, several proteins involved in redox balance were identified by mass spectrometry (eg, cyclophilin, thioredoxin reductase, catalase). Diminished catalase expression and activity were observed in PMNs from AAA patients compared with controls. In contrast, PMNs from AAA patients displayed higher H 2 O 2 and myeloperoxidase levels than PMNs from controls. Moreover, a significant decrease in catalase mRNA levels was observed in PMNs after phorbol 12-myristate 13-acetate incubation. Catalase plasma levels were also decreased in large (n=47) and small (n=56) AAA patients compared with controls (n=34). We observed catalase expression in AAA thrombus and thrombus-conditioned medium, associated with PMN infiltration. Furthermore, increased H 2 O 2 levels were observed in AAA thrombus-conditioned medium compared with the media layer.

Conclusion—

Diminished catalase levels in circulating PMNs and plasma are observed in AAA patients, supporting an important role of oxidative stress in AAA evolution.

Gaining new insights into early abdominal aortic aneurysm disease

Abdominal aortic aneurysm (AAA) disease is a prevalent and highly morbid condition among older people in the US. There are currently no proven methods for reducing or eliminating enlargement in smaller preclinical aneurysms. Given their relatively slow increase in diameter (typically <0.4 cm/year), these smaller aneurysms offer a valuable window into the underlying pathophysiology of AAA disease. Through a Vascular Remodeling Specialized Center of Clinically Oriented Research program funded by the National Institutes of Health, we have established, in conjunction with Northern California Kaiser Permanente, a multidisciplinary research effort to efficiently identify and handicap suppressive therapeutic strategies for early AAA disease.

Hemodynamic changes quantified in abdominal aortic aneurysms with increasing exercise intensity using mr exercise imaging and image-based computational fluid dynamics

Abdominal aortic aneurysm (AAA) is a vascular disease resulting in a permanent, localized enlargement of the abdominal aorta. We previously hypothesized that the progression of AAA may be slowed by altering the hemodynamics in the abdominal aorta through exercise [Dalman, R. L., M. M. Tedesco, J. Myers, and C. A. Taylor. Ann. N.Y. Acad. Sci. 1085:92-109, 2006]. To quantify the effect of exercise intensity on hemodynamic conditions in 10 AAA subjects at rest and during mild and moderate intensities of lower-limb exercise (defined as 33 ± 10% and 63 ± 18% increase above resting heart rate, respectively), we used magnetic resonance imaging and computational fluid dynamics techniques. Subject-specific models were constructed from magnetic resonance angiography data and physiologic boundary conditions were derived from measurements made during dynamic exercise. We measured the abdominal aortic blood flow at rest and during exercise, and quantified mean wall shear stress (MWSS), oscillatory shear index (OSI), and particle residence time (PRT). We observed that an increase in the level of activity correlated with an increase of MWSS and a decrease of OSI at three locations in the abdominal aorta, and these changes were most significant below the renal arteries. As the level of activity increased, PRT in the aneurysm was significantly decreased: 50% of particles were cleared out of AAAs within 1.36 ± 0.43, 0.34 ± 0.10, and 0.22 ± 0.06 s at rest, mild exercise, and moderate exercise levels, respectively. Most of the reduction of PRT occurred from rest to the mild exercise level, suggesting that mild exercise may be sufficient to reduce flow stasis in AAAs.

Current status of medical management for abdominal aortic aneurysm

Previous trials indicate that surgical management of small abdominal aortic aneurysms (AAA) does not reduce mortality. The medical management of AAA, however, has to a large degree been ignored until recently. Medical management is not only needed to limit the expansion of small AAAs but also to reduce the high incidence of other cardiovascular events in these patients. In this review current evidence regarding medical therapy for patients with small AAAs is discussed. Four current randomised controlled trials are examining the efficacy of exercise, doxycycline and angiotensin converting enzyme inhibition in limiting AAA progression. A further trial using a mast cell stabilisation agent is expected to start soon. It is anticipated that a range of novel therapies for small AAAs will be identified within the next decade.

Evolution of shear stress, protein expression, and vessel area in an animal model of arterial dilatation in hemodialysis grafts

PURPOSE

To evaluate the wall shear stress, protein expression of matrix metalloproteinase (MMP)-2 and MMP-9 and tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-2, and vessel area over time in a porcine model for polytetrafluoroethylene (PTFE) hemodialysis grafts.

MATERIALS AND METHODS

In 21 pigs, subtotal renal infarction was created, and 28 days later, a PTFE graft was placed to connect the carotid artery to the ipsilateral jugular vein. Phase-contrast magnetic resonance imaging was used to measure blood flow and vessel area at 1, 3, 7, and 14 days after graft placement. Wall shear stress was estimated from the law of Poiseuille. Animals were killed at day 3 (n = 7), day 7 (n = 7), and day 14 (n = 7) and expression of MMP-2, MMP-9, TIMP-1, and TIMP-2 were determined at the grafted and control arteries.

RESULTS

The mean wall shear stress of the grafted artery was higher than in the control artery at all time points (P < .05). It peaked by day 3 and decreased by days 7-14 as the vessel area nearly doubled. By days 7-14, there was a significant increase in active MMP-2 followed by a significant increase in pro-MMP-9 and active MMP-9 by day 14 (P < .05, grafted artery vs control). TIMP-1 expression peaked by day 7 and then decreased, whereas TIMP-2 expression was decreased at days 7-14.

CONCLUSIONS

The wall shear stress of the grafted artery peaks by day 3, with increased MMP-2 activity by days 7-14, followed by increase pro-MMP-9 and active MMP-9 by day 14. In addition, the vessel area nearly doubled.

Quantifying in vivo hemodynamic response to exercise in patients with intermittent claudication and abdominal aortic aneurysms using cine phase-contrast MRI

PURPOSE

To evaluate rest and exercise hemodynamics in patients with abdominal aortic aneurysms (AAA) and peripheral occlusive disease (claudicants) using phase-contrast MRI.

MATERIALS AND METHODS

Blood velocities were acquired by means of cardiac-gated cine phase-contrast in a 0.5 Tesla (T) open MRI. Volumetric flow was calculated at the supraceliac (SC), infrarenal (IR), and mid-aneurysm (MA) levels during rest and upright cycling exercise using an MR-compatible exercise cycle.

RESULTS

Mean blood flow increased during exercise (AAA: 130%, Claudicants: 136% of resting heart rate) at the SC and IR levels for AAA participants (2.6 +/- 0.6 versus 5.8 +/- 1.6 L/min, P < 0.001 and 0.8 +/- 0.4 versus 5.1 +/- 1.7 L/min, P < 0.001) and claudicants (2.3 +/- 0.5 versus 4.5 +/- 0.9 L/min, P < 0.005 and 0.8 +/- 0.2 versus 3.3 +/- 0.9 L/min, P < 0.005). AAA participants had a significant decrease in renal and digestive blood flow from rest to exercise (1.8 +/- 0.7 to 0.7 +/- 0.6 L/min, P < 0.01). The decrease in renal and digestive blood flow during exercise correlated with daily activity level for claudicants (R = 0.81).

CONCLUSION

Abdominal aortic hemodynamic changes due to lower extremity exercise can be quantified in patients with AAA and claudication using PC-MRI. The redistribution of blood flow during exercise was significant and different between the two disease states.

Hemodynamic influences on abdominal aortic aneurysm disease: Application of biomechanics to aneurysm pathophysiology

"Atherosclerotic" abdominal aortic aneurysms (AAAs) occur with the greatest frequency in the distal aorta. The unique hemodynamic environment of this area predisposes it to site-specific degenerative changes. In this review, we summarize the differential hemodynamic influences present along the length of the abdominal aorta, and demonstrate how alterations in aortic flow and wall shear stress modify AAA progression in experimental models. Improved understanding of aortic hemodynamic risk profiles provides an opportunity to modify patient activity patterns to minimize the risk of aneurysmal degeneration.

Quantification of hemodynamics in abdominal aortic aneurysms during rest and exercise using magnetic resonance imaging and computational fluid dynamics

Abdominal aortic aneurysms (AAAs) affect 5-7% of older Americans. We hypothesize that exercise may slow AAA growth by decreasing inflammatory burden, peripheral resistance, and adverse hemodynamic conditions such as low, oscillatory shear stress. In this study, we use magnetic resonance imaging and computational fluid dynamics to describe hemodynamics in eight AAAs during rest and exercise using patient-specific geometric models, flow waveforms, and pressures as well as appropriately resolved finite-element meshes. We report mean wall shear stress (MWSS) and oscillatory shear index (OSI) at four aortic locations (supraceliac, infrarenal, mid-aneurysm, and suprabifurcation) and turbulent kinetic energy over the entire computational domain on meshes containing more than an order of magnitude more elements than previously reported results (mean: 9.0-million elements; SD: 2.3 M; range: 5.7-12.0 M). MWSS was lowest in the aneurysm during rest 2.5 dyn/cm(2) (SD: 2.1; range: 0.9-6.5), and MWSS increased and OSI decreased at all four locations during exercise. Mild turbulence existed at rest, while moderate aneurysmal turbulence was present during exercise. During both rest and exercise, aortic turbulence was virtually zero superior to the AAA for seven out of eight patients. We postulate that the increased MWSS, decreased OSI, and moderate turbulence present during exercise may attenuate AAA growth.

Digging in the "soil" of the aorta to understand the growth of abdominal aortic aneurysms

Extensive studies into the etiology of aortic aneurysm disease have focused on the characteristic and unique inflammatory infiltration and elaboration of products of inflammatory cells which can result in matrix degradation. While these changes clearly have a significant impact on the development of aneurysm disease, little attention has been paid to the changes in the parenchymal cells of the aorta. Under normal conditions, the vascular smooth muscle cells which populate the aortic wall are responsible for the maintenance of the matrix components of the media, particularly the elastic fibers. As our understanding of the mechanisms of aneurysm formation and normal arterial anatomy become more sophisticated, it is clear that specific changes to these smooth muscle cells make them active participants in the medial matrix destruction characteristic of aneurysm disease. As others have described for intimal arterial disease, this is the "soil" from which aortic aneurysms grow.

Apelin prevents aortic aneurysm formation by inhibiting macrophage inflammation

Apelin is a potent inodilator with recently described antiatherogenic properties. We hypothesized that apelin might also attenuate abdominal aortic aneurysm (AAA) formation by limiting disease-related vascular wall inflammation. C57BL/6 mice implanted with osmotic pumps filled with apelin or saline were treated with pancreatic elastase to create infrarenal AAAs. Mice were euthanized for aortic PCR analysis or followed ultrasonographically and then euthanized for histological analysis. The cellular expression of inflammatory cytokines and chemokines in response to apelin was also assessed in cultured macrophages, smooth muscle cells, and fibroblasts. Apelin treatment resulted in diminished AAA formation, with a 47% reduction in maximal cross-sectional area (0.74 vs. 1.39 mm(2), P < 0.03) and a 57% reduction in macrophage infiltrate (113 vs. 261.3 cells/high-power field, P < 0.0001) relative to the saline-treated group. Apelin infusion was also associated with significantly reduced aortic macrophage colony-stimulating factor expression and decreased monocyte chemattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1alpha, interleukin (IL)-6, and tumor necrosis factor (TNF)-alpha mean mRNA levels. Apelin stimulation of cultured macrophages significantly reduced MCP-1 and TNF-alpha mRNA levels relative to baseline (2.03- and 1.89-fold reduction, P < 0.03, respectively) but did not affect intimal adhesion molecule expression or medial or adventitial cell cytokine production. Apelin significantly reduces aneurysm formation in the elastase model of human AAA disease. The mechanism appears to be decreased macrophage burden, perhaps related to an apelin-mediated decrease in proinflammatory cytokine and chemokine activation.

Identifying abdominal aortic aneurysm risk factors in postmenopausal women

Evaluation of: Lederle FA, Larson JC, Margolis KL et al.: Abdominal aortic aneurysm events in the Women's Health Initiative: cohort study. Br. Med. J. 337, A1724 (2008). A linked cohort study of 161,808 postmenopausal women aged 50-79 years enrolled in the Women's Health Initiative was conducted during which participants were followed for the incidence of abdominal aortic aneurysm repair or rupture. This study evaluated the association between potential risk factors and subsequent abdominal aortic aneurysm events in women. A total of 467 women reported a diagnosis of abdominal aortic aneurysm before entering the study or during participation, with 184 aneurysm-related events identified. Abdominal aortic aneurysm events were strongly associated with age and smoking and negatively associated with diabetes and baseline use of postmenopausal hormone supplementation. Previous studies investigating abdominal aortic aneurysm have focused primarily on men, with little reliable information available on women. This study contributes a large female cohort to provide better insight into gender-specific abdominal aortic aneurysm risks and disease associations.