Systemic levels of cotinine and elastase, but not pulmonary function, are associated with the progression of small abdominal aortic aneurysms

Plasma complement component C2: a potential biomarker for predicting abdominal aortic aneurysm related complications

Blood-based adjunctive measures that can reliably predict abdominal aortic aneurysm (AAA)-related complications hold promise for mitigating the AAA disease burden. In this pilot study, we sought to evaluate the prognostic performance of complement factors in predicting AAA-related clinical outcomes. We recruited consecutive AAA patients (n = 75) and non-AAA patients (n = 75) presenting to St. Michael's Hospital. Plasma levels of complement proteins were assessed at baseline, as well as prospectively measured regularly over a period of 2 years. The primary outcome was the incidence of rapidly progressing AAA (i.e. aortic expansion), defined as change in AAA diameter by either 0.5 cm in 6 months, or 1 cm in 12 months. Secondary outcomes included incidence of major adverse aortic events (MAAE) and major adverse cardiovascular events (MACE). All study outcomes (AAA diameter, MACE and MAAE) were obtained during follow-up. Multivariable adjusted Cox regression analyses were performed to assess the prognostic value of plasma C2 levels in patients with AAA regarding rapid aortic expansion and MAAE and MACE. Event-free survival rates of both groups were also compared. Compared to non-AAA patients, patients with AAA demonstrated significantly higher plasma concentrations of C1q, C4, Factor B, Factor H and Factor D, and significantly lower plasma concentrations of C2, C3, and C4b (p = 0.001). After a median of 24 months from initial baseline measurements, C2 was determined as the strongest predictor of rapid aortic expansion (HR 0.10, p = 0.040), MAAE (HR 0.09, p = 0.001) and MACE (HR 0.14, p = 0.011). Based on the data from the survival analysis, higher levels of C2 at admission in patients with AAA predicted greater risk for rapid aortic expansion and MAAE (not MACE). Plasma C2 has the potential to be a biomarker for predicting rapid aortic expansion, MAAE, and the eventual need for an aortic intervention in AAA patients.

Systematic Review of Circulating, Biomechanical, and Genetic Markers for the Prediction of Abdominal Aortic Aneurysm Growth and Rupture

BACKGROUND

The natural course of abdominal aortic aneurysms (AAA) is growth and rupture if left untreated. Numerous markers have been investigated; however, none are broadly acknowledged. Our aim was to identify potential prognostic markers for AAA growth and rupture.

METHODS AND RESULTS

Potential circulating, biomechanical, and genetic markers were studied. A comprehensive search was conducted in PubMed, Embase, and Cochrane Library in February 2017, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Study selection, data extraction, and methodological quality assessment were conducted by 2 independent researchers. Plausibility of markers was based on the amount of publications regarding the marker (more than 3), pooled sample size (more than 100), bias risk and statistical significance of the studies. Eighty-two studies were included, which examined circulating (n=40), biomechanical (n=27), and genetic markers (n=7) and combinations of markers (n=8). Factors with an increased expansion risk included: AAA diameter (9 studies; n=1938; low bias risk), chlamydophila pneumonia (4 studies; n=311; medium bias risk), S-elastin peptides (3 studies; n=205; medium bias risk), fluorodeoxyglucose uptake (3 studies; n=104; medium bias risk), and intraluminal thrombus size (5 studies; n=758; medium bias risk). Factors with an increased rupture risk rupture included: peak wall stress (9 studies; n=579; medium bias risk) and AAA diameter (8 studies; n=354; medium bias risk). No meta-analysis was conducted because of clinical and methodological heterogeneity.

CONCLUSIONS

We identified 5 potential markers with a prognostic value for AAA growth and 2 for rupture. While interpreting these data, one must realize that conclusions are based on small sample sizes and clinical and methodological heterogeneity. Prospective and methodological consonant studies are strongly urged to further study these potential markers.

Abdominal Aortic Aneurysms and Risk Factors for Adverse Events

An abdominal aortic aneurysm (AAA) is a focal full thickness dilatation of the abdominal aorta, greater than 1.5 times its normal diameter. Although some patients with AAA experience back or abdominal pain, most remain asymptomatic until rupture. The prognosis after AAA rupture is poor. Management strategies for patients with asymptomatic AAAs include risk factor reduction, such as smoking cessation, optimizing antihypertensive treatment, and treating dyslipidemia, as well as surveillance by ultrasound. Currently, aneurysm diameter alone is often used to assess risk of rupture. Once the aneurysm diameter reaches 5.5 cm, the risk of rupture is considered greater than the risk of intervention and elective aneurysm repair is undertaken. There is increasing interest in detecting AAAs early, and national screening programs are now in place. Furthermore, there is increasing research interest in biomarkers, genetics, and functional imaging to improve detection of AAAs at risk of progression and rupture. In this review, we discuss risk factors for AAA rupture, which should be considered during the management process, to advance current deficiencies in management pathways.

Asthma Associates With Human Abdominal Aortic Aneurysm and Rupture

OBJECTIVE

Both asthma and abdominal aortic aneurysms (AAA) involve inflammation. It remains unknown whether these diseases interact.

APPROACH AND RESULTS

Databases analyzed included Danish National Registry of Patients, a population-based nationwide case-control study included all patients with ruptured AAA and age- and sex-matched AAA controls without rupture in Denmark from 1996 to 2012; Viborg vascular trial, subgroup study of participants from the population-based randomized Viborg vascular screening trial. Patients with asthma were categorized by hospital diagnosis, bronchodilator use, and the recorded use of other anti-asthma prescription medications. Logistic regression models were fitted to determine whether asthma associated with the risk of ruptured AAA in Danish National Registry of Patients and an independent risk of having an AAA at screening in the Viborg vascular trial. From the Danish National Registry of Patients study, asthma diagnosed <1 year or 6 months before the index date increased the risk of AAA rupture before (odds ratio [OR]=1.60-2.12) and after (OR=1.51-2.06) adjusting for AAA comorbidities. Use of bronchodilators elevated the risk of AAA rupture from ever use to within 90 days from the index date, before (OR=1.10-1.37) and after (OR=1.10-1.31) adjustment. Patients prescribed anti-asthma drugs also showed an increased risk of rupture before (OR=1.12-1.79) and after (OR=1.09-1.48) the same adjustment. In Viborg vascular trial, anti-asthmatic medication use associated with increased risk of AAA before (OR=1.45) or after adjustment for smoking (OR=1.45) or other risk factors (OR=1.46).

CONCLUSIONS

Recent active asthma increased risk of AAA and ruptured AAA. These findings document and furnish novel links between airway disease and AAA, 2 common diseases that share inflammatory aspects.

Surrogate Markers of Abdominal Aortic Aneurysm Progression

The natural course of many abdominal aortic aneurysms (AAA) is to gradually expand and eventually rupture and monitoring the disease progression is essential to their management. In this publication, we review surrogate markers of AAA progression. AAA diameter remains the most widely used and important marker of AAA growth. Standardized reporting of reproducible methods of measuring AAA diameter is essential. Newer imaging assessments, such as volume measurements, biomechanical analyses, and functional and molecular imaging, as well as circulating biomarkers, have potential to add important information about AAA progression. Currently, however, there is insufficient evidence to recommend their routine use in clinical practice.

Circulating tetrahydrobiopterin as a novel biomarker for abdominal aortic aneurysm

Rupture of abdominal aortic aneurysm (AAA) is unpredictable and lethal. A clinically valid biomarker to monitor the disease has not been available. Based on our recent discoveries that uncoupled endothelial nitric oxide synthase (eNOS)/tetrahydrobiopterin deficiency plays a causal role in various models of AAA, the present study examined the relationship between circulating and tissue levels of tetrahydrobiopterin (H4B) in angiotensin II-infused hyperphenylalaninemia (hph-1) and apoE null mice. For apoE null mice, tissue and plasma H4B levels decreased time dependently, to 2.69 ± 0.15 and 1.99 ± 0.06 pmol/mg, respectively (from 4.86 ± 0.32 and 3.31 ± 0.13 pmol/mg at baseline) by week 3, when aneurysms developed. For hph-1 mice, tissue and plasma H4B levels decreased significantly to 1.02 ± 0.10 and 0.98 ± 0.09 pmol/mg, respectively (from 1.84 ± 0.18 and 1.48 ± 0.12 pmol/mg at baseline), by week 1, when aneurysms developed. Oral folic acid administration, which has been shown to improve aortic H4B levels to completely prevent or markedly decrease the incidence of AAA, significantly increased tissue and plasma H4B levels in both animal models starting at week 1. The two H4B measurements at all conditions showed significant linear correlation, suggesting that plasma H4B accurately predicts its tissue levels when H4B is either reduced or enhanced. Together, these data demonstrate that H4B levels decrease with AAA development and increase with folic acid treatment in two different murine models of AAA and that plasma H4B levels accurately reflect H4B levels in the tissue, suggesting that circulating H4B levels may be used clinically as a novel and powerful biomarker for the development and response to treatment of AAA.

The influence of smoking on endovascular abdominal aortic aneurysm repair

OBJECTIVE

The main purpose of this study was to evaluate the influence of smoking on perioperative outcomes of endovascular aneurysm repair (EVAR), aneurysm sac behavior, abdominal aortic aneurysm (AAA) neck growth after EVAR, and its effect on stent graft migration during follow-up.

METHODS

Baseline characteristics and follow-up data were collected prospectively by patient record forms. Follow-up visits were scheduled at 1, 3, 6, 12, 18, and 24 months, and annually thereafter and included a clinical examination and imaging studies. Patients were stratified in three groups according to their smoking status as nonsmokers, former smokers, and smokers.

RESULTS

This study analyzed the data for 4176 nonsmokers, 2406 former smokers, and 2056 smokers who were enrolled prospectively in the European Collaborators on Stent-Graft Techniques for Aortic Aneurysm Repair (EUROSTAR) database. Compared with nonsmokers, smokers required more percutaneous transluminal angioplasty and stent placements during EVAR (P < .001), and stent graft migration occurred more often (hazard ratio, 1.45; 95% confidence interval, 1.03-2.05; P = .033). Nonsmokers had more late type II endoleaks than former smokers and smokers (58.5%, 55.9%, and 35.5%, respectively; P < .001). Smoking had no effect on aneurysm sac behavior or AAA neck growth after EVAR.

CONCLUSIONS

Smokers need more percutaneous transluminal angioplasty procedures and stents during EVAR. They have fewer late type II endoleaks during follow-up; however, smokers should be closely monitored because they have an increased risk of stent graft migration.

Socioeconomic position, comorbidity, and mortality in aortic aneurysms: a 13-year prospective cohort study

BACKGROUND

To evaluate factors associated with incidence and 3-year all-cause mortality in patients with aortic aneurysm (AA). The design is sex and age-stratified (60-79 and 80-90 years) prospective cohort. By using the population register, we constituted a cohort of all men and women born between 1900 and 1930 and living in Scania by 1991, and followed them for 13 years. Identification of AA was based on hospital discharge diagnosis obtained from the Swedish Patient Register or from the information on death certificates from the Cause of Death Register.

METHODS

We applied stepwise Cox regression and investigated both AA incidence (1991-2003) as well as 3-year survival after the first hospitalization for AA.

RESULTS

We found an inverse relation between AA incidence and previous hospitalization by diabetes mellitus in women (hazard ratio [HR]: 0.41; 95% confidence interval [CI]: 0.19-0.88) and in men (HR: 0.38; 95% CI: 0.24-0.61) aged 60-79 years. Three-year all-cause mortality after diagnosis of AA was 58.6% in women, 50.2% in men, 72.9% in octogenarians, and 43.7% for nonoctogenarians. Low income, chronic respiratory diseases, cerebrovascular diseases, dementia, systemic connective tissue disorders, renal failure, and malignant neoplasms were independent factors for mortality in 60-79-year-old men with AA.

CONCLUSIONS

Inferior socioeconomic position is associated with increased 3-year all-cause mortality in 60-79-year-old men with AA.

Evaluating smooth muscle cells from CaCl2-induced rat aortal expansions as a surrogate culture model for study of elastogenic induction of human aneurysmal cells

Regression of abdominal aortic aneurysms (AAAs) via regeneration of new elastic matrix is constrained by poor elastin synthesis by adult vascular cells and absence of methods to stimulate the same. We recently showed hyaluronan oligomers (HA-o) and TGF-β1 (termed elastogenic factors) to enhance elastin synthesis and matrix formation by healthy rat aortic smooth muscle cells (RASMCs). We also determined that these factors could likewise elastogenically induce aneurysmal RASMCs isolated from periadventitial CaCl(2)-injury induced rat AAAs (aRASMCs). However, the factor doses should be increased for these diseased cell types, as even when induced, elastic matrix amounts are roughly one order of magnitude lower than those produced by healthy RASMCs. We presently investigate the dose-specific elastogenic effects of HA-o (0-20  μg/mL) and TGF-β1 (0-10  ng/mL) factors on aRASMCs and compare their phenotype and elastogenic responses to those of human AAA-derived SMCs (aHASMCs); we seek to determine whether aRASMCs are appropriate surrogate cell types to study in the context of inducing elastic matrix regeneration within human AAAs. The periadventitial CaCl(2)-injury model of AAAs exhibits many of the pathological characteristics of human AAAs, including similarities in terms of decreased SMC contractile activity, enhanced proliferation, and reduced elastogenic capacity of aneurysmal SMCs (relative to healthy SMCs) when isolated and expanded in culture. Both aRASMCs and aHASMCs can be elastogenically stimulated by HA-o and TGF-β1 and show broadly similar trends in their dose-specific responses to these factors. However, compared with aHASMCs, aRASMCs appear to be far less elastogenically inducible. This may be due to differences in maturity of the AAAs studied, with the CaCl(2)-injury induced aortal expansion barely qualifying as an aneurysm and the human AAA representing a more well-developed condition. Further study of SMCs from stage-matched CaCl(2)-injury induced rat aortal expansions and human AAAs will be necessary to more rigorously evaluate their basal and induced elastogenic responses.

Elastogenic inductability of smooth muscle cells from a rat model of late stage abdominal aortic aneurysms

Although abdominal aortic aneurysms (AAA) can be potentially stabilized by inhibiting inflammatory cell recruitment and their release of proteolytic enzymes, active AAA regression is not possible without regeneration of new elastic matrix structures. Unfortunately, postneonatal vascular smooth muscle cells (SMCs), healthy, and likely more so, diseased cells, poorly synthesize or remodel elastic fibers, impeding any effort directed at regenerative AAA treatment. Previously, we determined the eleastogenic benefits of oligomers (HA-o; 4-6 mers) of the glycosaminoglycan, hyaluronan (HA) and transforming growth factor-β1 (TGF-β1) to healthy SMCs. Since AAAs are often diagnosed only late in development when matrix disruption is severe, we now determine if elastogenic upregulation of SMCs from late-stage AAAs (>100% diameter increase) is possible. AAAs were induced by perfusion of rat infrarenal aortae with porcine pancreatic elastase. Elastic matrix degradation, vessel expansion (∼120%), inflammatory cell infiltration, and enhanced activity of matrix-metalloproteases (MMPs) 2 and 9 resulted, paralleling human AAAs. Aneurysmal SMCs (EaRASMCs) maintained a diseased phenotype in 2D cell culture and exhibited patterns of gene expression different from healthy rat aortic SMCs (RASMCs). Relative to passage-matched healthy RASMCs, unstimulated EaRASMCs produced far less tropoelastin and matrix elastin. Exogenous TGF-β and HA-o (termed "factors") significantly decreased EaRASMC proliferation and enhanced tropoelastin synthesis, though only at the highest provided dose combination (20 mg/mL of HA-o, 10 ng/mL of TGF-β); despite such enhancement, tropoelastin amounts were only ∼40% of amounts synthesized by healthy RASMC cultures. Differently, elastic matrix synthesis was enhanced beyond amounts synthesized by healthy RASMCs (112%), even at lower doses of factors (2 mg/mL of HA-o and 5 ng/mL of TGF-β). The factors also enhanced elastic fiber deposition over untreated EaRASMC cultures and restored several genes whose expression was altered in EaRASMC cultures back to levels expressed by healthy RASMCs. However, the activity of MMPs 2 and 9 generated by EaRASMC cultures was unaffected by the factors/factor dose. The study confirms that SMCs from advanced AAAs can be elastogenically induced, although much higher doses of elastogenic factors are required for induction relative to healthy SMCs. Also, the factors do not appear to inhibit MMP activity, vital to preserve existing elastic matrix structures that serve as nucleation sites for new elastic fiber deposition. Thus, to enhance net accumulation of newly regenerated elastic matrix, toward possibly regressing AAAs, codelivery of MMP inhibitors may be necessitated.

Novel aspects of the pathogenesis of aneurysms of the abdominal aorta in humans

Aneurysm of the abdominal aorta (AAA) is a particular, specifically localized form of atherothrombosis, providing a unique human model of this disease. The pathogenesis of AAA is characterized by a breakdown of the extracellular matrix due to an excessive proteolytic activity, leading to potential arterial wall rupture. The roles of matrix metalloproteinases and plasmin generation in progression of AAA have been demonstrated both in animal models and in clinical studies. In the present review, we highlight recent studies addressing the role of the haemoglobin-rich, intraluminal thrombus and the adventitial response in the development of human AAA. The intraluminal thrombus exerts its pathogenic effect through platelet activation, fibrin formation, binding of plasminogen and its activators, and trapping of erythrocytes and neutrophils, leading to oxidative and proteolytic injury of the arterial wall. These events occur mainly at the intraluminal thrombus-circulating blood interface, and pathological mediators are conveyed outwards, where they promote matrix degradation of the arterial wall. In response, neo-angiogenesis, phagocytosis by mononuclear cells, and a shift from innate to adaptive immunity in the adventitia are observed. Abdominal aortic aneurysm thus represents an accessible spatiotemporal model of human atherothrombotic progression towards clinical events, the study of which should allow further understanding of its pathogenesis and the translation of pathogenic biological activities into diagnostic and therapeutic applications.

Utility of hyaluronan oligomers and transforming growth factor-beta1 factors for elastic matrix regeneration by aneurysmal rat aortic smooth muscle cells

The progression of aortic aneurysms (AAs) is typically associated with an activated smooth muscle cell (SMC) phenotype, diminished density of mature medial elastic fibers, and an elevated presence of matrix-degrading enzymes, which ultimately leads to vessel rupture. Currently, no surgical or nonsurgical methods are available to regress aneurysms via regeneration of new elastic matrices, particularly because of inherently poor elastin synthesis by adult vascular cells and absence of tools to stimulate the same. We seek to address this void in this study. We recently showed 0.2 microg/mL of hyaluronan oligomers and 1 ng/mL of transforming growth factor-beta1 (termed elastogenic factors) to dramatically enhance elastin synthesis and matrix formation by healthy aortic SMCs. In this study, the effect of these factors, alone or together, on suppressing procalcific and elastolytic activities of aneurysmal vascular cells, and improving their elastin matrix synthesis and assembly is examined. Periadventitial injury with calcium chloride was used to induce AAs in rats, and approximately 45% increase in aortic diameter was observed after 4 weeks. Aneurysmal SMCs isolated from these AA segments produced higher levels of inflammatory markers matrix metalloproteinases-2 and 9 elastase activity and calcific deposits, while synthesizing significantly less collagen, tropoelastin, and matrix elastin proteins over a 3-week culture period, relative to healthy SMCs. While hyaluronan oligomers alone significantly suppressed aneurysmal cell proliferation and promoted 20-50% increases in collagen and elastin synthesis (p < 0.01), transforming growth factor-beta1 alone had no effect on cellular proliferation and elastin synthesis. However, provision of factors together resulted in significantly higher amounts of collagen/elastin protein synthesis and crosslinking, by upregulating lysyl oxidase and desmosine. Compared to their individual contributions, the factors together were highly effective in minimizing the release of inflammatory enzymes, and encouraging elastic fiber formation. Since elastic matrix amounts were one order of magnitude lower than that observed with healthy cells, even upon elastogenic stimulation at doses optimized previously for healthy cells, increased doses are likely required and must be reoptimized for diseased cells. Despite this, the results point to the potential utility of these elastogenic factors in regenerating elastic matrices within AAs.

Smoking is a major risk factor for wound dehiscence after midline abdominal incision; case-control study

BACKGROUND

The incidence of acute fascial wound dehiscence (AFWD) after major abdominal operations is as high as 3%. AFWD is associated with mortality rates of 15-20%. Male gender, advanced age and numerous systemic factors including malignancy hypoproteinemia and steroid use have been associated with increased risk. The aim of the present study was to investigate the association between smoking prevalence and AFWD.

METHODS

Middlemore Hospital records were retrieved from the 1997-2006 period for patients who had undergone midline abdominal surgery and developed AFWD. A return to the operating theatre for closure of the fascial dehiscence was required for study group inclusion. Each patient in the study group was matched to two control patients who had been admitted in the same year for surgery and who had a similar initial surgical intervention. Conditional logistic regression was used to calculate odds ratios with 95% confidence intervals, representing the risk of developing fascial wound dehiscence in smokers compared with the non-smoking group.

RESULTS

There were 52 patients (32 male, 20 female) and 104 controls (64 male, 40 female). Median age for both groups was 63 years. A history of heavy tobacco use (> or =20 pack-years) was more prevalent in those who had AFWD (46%) compared with the control group (16%; P = 0.0002; odds ratio 3.7).

CONCLUSIONS

Smoking is associated with an increased incidence of acute fascial wound dehiscence following laparotomy. It is not known whether smoking is a causal or a surrogate factor.

Potential circulating biomarkers for abdominal aortic aneurysm expansion and rupture--a systematic review

BACKGROUND

The maximal diameter of abdominal aortic aneurysms (AAAs) is the dominating indication for repair. However half of the AAAs repaired would never have ruptured if left unrepaired, although small AAAs occasionally rupture. Earlier surgery may be associated with a lower mortality. More precise indicators for surgery are warranted. This systematic review identifies potential systemic biomarkers for AAA rupture or expansion.

METHODS

MEDLINE/PubMed and EMBASE (from 1985 trough May 2007) were searched with the medical subject heading abdominal aortic aneurysm and keywords "size", "progression" or "growth" or "expansion rate" or "rupture" on the basis of MESH tree and as a text search restricted to English, German, French and Italian. In addition, reference lists were studied and manual searches performed. Observational studies investigating the association of circulating biomarkers with AAA rupture, expansion or size were selected.

DATA EXTRACTION

Two reviewers (SU and GU) independently extracted the following data: year of publication, study characteristics, duration of follow-up, circulating biomarker, AAA expansion rate or size or rupture.

RESULTS

699 papers were identified. After exclusion of thoracic aneurysms and cardiac studies (n=118), surgical or medical treatment studies (n=179), case reports and animal studies (n=87), as well as reviews or letters (n=66), 249 articles were selected. Also excluded were 230 papers that did not report AAA size, expansion rate or rupture. 39 papers were included. Several potential biomarkers were identified. The strongest association with AAA was obtained with serum elastin peptides (SEP) and plasmin-antiplasmin (PAP) complexes. Matrix-degrading metalloproteinase 9 (MMP9) and interferon-gamma (IFN-gamma) could have clinical potential while many putative biomarkers showed poor association.

CONCLUSIONS

Several circulating agents in peripheral blood may predict AAA size, expansion rate or rupture. Few of them have clinical potential for future use. Confirmative studies and development of multivariate models are needed, together with continuing search for new biomarkers using the discovery based sciences within proteomics and/or genomics.

The Role of Smoking in Abdominal Aortic Aneurysm Development

Abdominal aortic aneurysm is common. The aim of this study was to assess the effect of smoking on prevalence and management. Patients attending the vascular unit and appropriate controls were prospectively recruited. A smoking history revealed tobacco exposure in pack years. Serum cotinine was assessed biochemically. Independent risk factors were statistically determined. In all, 202 (186 men) patients were recruited, with 202 (197 men) controls. A total of 69 patients tested positive for cotinine, whereas 39 controls were positive ( P = .001). Smoking and ischemic heart disease were significant predictors for aneurysm prevalence. Cardiac disease emerged as a more important predictor than smoking in symptomatic patients. In noncardiac patients, smoking and hypercholesterolemia were significant risk factors. Smoking is a significant predictor for aneurysm development. In high-risk patients, the cardiac disease process is the most important factor, with control of this imperative. However, in noncardiac patients, smoking cessation and lipid-lowering therapy are crucial.

Acute abdominal vascular emergencies

Abdominal vascular emergencies are relatively uncommon, frequently catastrophic, and highly lethal. Despite improved understanding of the pathophysiology and natural history of these disorders, delays in diagnosis and treatment remain the most important factors contributing to the observed high mortality. A high index of clinical suspicion together with a sound understanding of the clinical presentation, natural history, and management of these disorders are critical to improving outcomes. This article focuses on abdominal vascular emergencies presenting with acute visceral ischemia or catastrophic intra-abdominal hemorrhage.

Effect of smoking on abdominal aortic aneurysms: novel insights through murine models

Abdominal aortic aneurysm is a poorly understood and fatal disease. The etiology of the disease is believed to be multifactorial. Of all the recognized clinical associations, none has a greater impact on the incidence and progression of the disease than exposure to tobacco smoke. Novel murine models developed over the past several years present the opportunity to investigate the mechanism of this critical clinical relationship.

Cigarette smoking increases aortic dilatation without affecting matrix metalloproteinase-9 and -12 expression in a modified mouse model of aneurysm formation

OBJECTIVE

The development of abdominal aortic aneurysms (AAA) is presumed to result from multiple genetic and environmental factors, with exposure to tobacco smoke the single largest known factor predisposing to aneurysm growth. We have attempted to adapt the elastase-perfused animal model to determine whether tobacco exposure can lower the threshold of aortic injury necessary for AAA development.

METHODS

Adult C57BL/6 mice underwent transient perfusion of the infrarenal aorta with an active solution of elastase: high-dose (HDE, 0.19 U/mL, n=9), standard-dose (SDE, 0.16 U/mL, n=21) or low-dose (LDE, 0.07 U/mL, n=24). Control animals (n=24) were treated with heat inactivated elastase (HIE). Twenty LDE perfused mice were exposed to cigarette smoke (LDE-S) beginning 2 weeks before perfusion and continuing until aortic harvest. Aortic diameter (AD) was measured preperfusion, postperfusion, and at harvest on day 14. AAA was defined as %DeltaAD>or=100% between preperfusion and harvest. Aortas from each group (except HDE) were analyzed for matrix metalloproteinase-9 (MMP-9) and MMP-12 expression by real-time polymerase chain reaction normalized to glyceraldehyde-3-phosphate dehydrogenase.

RESULTS

All SDE mice developed large AAA by %DeltaAD (189.3%+/-16.9%, mean+/-standard error of the mean), but control mice had only a small dilatation (69.7%+/-3.7%, P<.01). Higher doses of elastase did not produce larger aneurysms in HDE mice. In contrast, only 63% of LDE mice showed aneurysmal dilatation, and these were significantly smaller (104.3%+/-4.2%, P<.01). When exposed to cigarette smoke, LDE animals developed significantly larger aneurysms (%DeltaAD, 134.5%+/-7.9%, P=.0021). There was no difference in normalized aortic MMP-9 and MMP-12 expression between elastase doses or between smoke-exposed and unexposed animals. Histologic analysis revealed that smoking increased the extent of aortic elastin degradation when compared with LDE-S animals.

CONCLUSION

Aneurysm development in the elastase model is dependent on the quantity of active elastase infused. Exposure of animals to tobacco smoke after a relatively minor aortic elastase injury produces increases in elastin degradation and aneurysm size without affecting MMP-9 or MMP-12 expression. To our knowledge, this is the first demonstration in an animal model that smoking can act as a synergistic factor in AAA development. Further understanding of the relationship between smoking and AAA in this model may help unveil the pathophysiologic pathways involved between cigarette smoke and AAAs.

Relatively High Pulmonary and Cardiovascular Mortality Rates in Screening-detected Aneurysmal Patients Without Previous Hospital Admissions

BACKGROUND

Men with abdominal aortic aneurysm (AAA) who are not hospitalised for pulmonary and cardiovascular diseases may have higher mortality due to such disorders.

MATERIAL AND METHODS

Previous discharge diagnoses and causes of death were collected for 4,816 men aged 64-73 years attending mass screening for AAA. Of these, 191 (4%) had an AAA. Overall, cardiovascular- and pulmonary-disease-specific mortality was compared for men with and without AAA stratified for earlier pulmonary or cardiovascular hospitalisations by Cox's proportional hazards regression while adjusting for age. Absolute risk differences after five years were calculated by life table analysis.

RESULTS

The median observation time was 63 months. 362 men died from cardiovascular causes other than AAA, and 144 died from pulmonary causes. The cardiovascular mortality was significantly higher in aneurysm patients without previous related hospitalisation (HR=4.35, 95% CI: 2.73-6.94, P<0.001) with an absolute mortality difference after 5 years of 16.3% (95% CI: 10.2-22.5%). Pulmonary-cause mortality was higher among men with AAA both with and without previous hospitalisation for pulmonary causes (HR=3.05; 95% CI: 1.19-7.83, P=0.020, and HR=3.29; 95% CI: 1.78-6.08, P<0.001, respectively).

CONCLUSIONS

Men with AAA who had not been hospitalised for cardiovascular diseases have more than four times higher cardiovascular mortality. Studies of cohorts being offered relevant prophylaxis may clarify the potential benefits of general preventive actions.

Smoking and Aortic Diseases

Cigarette smoking is a major vascular risk factor and in this context, it is an independent risk factor for the development of aortic disease, especially the formation and growth of abdominal aortic aneurysms (AAA). Medline was searched up to January 31, 2007 for the relevant literature for this review of the mechanisms by which smoking causes aortic wall damage and its subsequent impact on the clinical manifestation of this process. Idiopathic AAAs and aortic dissection are considered, as well as other aortic diseases (eg, Takayasu, Kawasaki, Behcet and Buerger). There is evidence suggesting an abnormal homeostasis between proteolytic and antiproteolytic activity in the vascular wall during the development of AAAs, and these mechanisms can be influenced by smoking. Smoking cessation plays an important role in the management of aortic disease.

Activators of Plasminogen and the Progression of Small Abdominal Aortic Aneurysms

The aim of this study was to examine the role of activating pathways of plasminogen in the natural history of abdominal aortic aneurysms (AAA). To fulfill this objective 70 male patients with small AAA (> 3 cm) were interviewed and examined. Their blood samples were taken at diagnosis. The patients were scanned annually for a minimum period of 1 year and a maximum of 5 years (mean 2.5 years), and referred for surgery if the AAA exceeded 5 cm in diameter. Plasma levels of urokinase-like plasminogen activator (uPA), tissue-type plasminogen activator (tPA), plasminogen-activator-inhibitor-1 (PAI-1), macrophage-inhibiting factor (MIF), transforming-growth-factor-beta1 (TGF-beta1), homocysteine, and serum levels of IgA-antibodies against Chlamydia pneumoniae (IgA-CP) and cotinine (a nicotine metabolite) were measured. The annual expansion rate correlated positively with tPA, IgA-CP, and S-cotinine; rho = 0.37 (P = 0.004), 0.28 (P = 0.01), and 0.24 (P = 0.04), while PAI-1, uPA, TGF-beta1, homocysteine, and MIF did not. S-cotinine and PAI-1 also correlated positively with tPA, rho = 0.24 (P = 0.04), and 0.33 (P = 0.005). IgA-CP did not correlate with tPA. By receiver operating characteristics (ROC) curve analysis, tPA showed to be predictive of cases expanding to above 5 cm within the first 5 years with an optimal sensitivity and specificity of 0.73 and 0.71, respectively (P = 0.015). The aortic matrix degradation in AAA may be partly caused by an activation of plasminogen by tPA, but not by uPA, which usually dominates matrix degradation. Smoking seems to be an important factor for this pathway, while the pathway of IgA-CP seems different.

Effect of lifestyle, gender and age on collagen formation and degradation

Historically, inappropriate lifestyle with an inadequate dietary intake of vitamin C has been associated with poor wound healing as a clinical manifestation of scurvy. In modern times, clinical evidence produced over the past few decades indicates that a modern lifestyle factor, such as smoking, together with biologic characteristics, like old age and male gender, are risk factors for abdominal wall hernia and recurrence. The pathologic pathways for these clinical observations are unclear. Yet, evidence from animal and human studies suggests that these exogenous and endogenous factors may have a negative impact on collagen metabolism, enhancing degradation and impairing formation.

Chronic Inflammation, Immune Response, and Infection in Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAA) are associated with atherosclerosis, transmural degenerative processes, neovascularization, decrease in content of vascular smooth muscle cells, and a chronic infiltration, mainly located in the outer aortic wall. The chronic infiltration consists mainly of macrophages, lymphocytes, and plasma cells. The dominant cells are Th2 restricted CD3+ lymphocytes expressing interleukine 4, 5, 8, and 10, and tumor necrosis factor-alpha for regulation of the local immune response. They also produce interferon-gamma and CD40 ligand to stimulate surrounding cells to produce matrix metalloproteases and cysteine proteases for aortic matrix remodeling. The lymphocyte activation may be mediated by microorganisms as well as autoantigens generated from vascular structural proteins, perhaps through molecular mimicry. As in autoimmune diseases, the risk of AAA is increased by certain genotypes concerning human leucocyte antigen class II. These types are also associated with increased aneurysmal inflammation indicating a genetic susceptibility to aortic inflammation. Chlamydia pneumoniae is often detected in AAA but the validity of the methods can be questioned, and two small antibiotic trials have been disappointing. However, serum antibodies against C. pneumoniae have been associated with AAA growth and cross-react with AAA wall proteins. Thus, immune responses mediated by microorganisms and autoantigens may play a pivotal role in AAA pathogenesis.

Pulmonary and cardiovascular consequences of smoking

The extensive worldwide disease burden attributable to tobacco smoking is reviewed, with particular attention to the epidemiologic and clinical aspects, molecular and cellular mechanisms, and pathophysiology of a variety of smoking-related pulmonary diseases, and the epidemiology and clinical presentation of smoking-related atherosclerotic disease as it affects the cardiovascular system cerebral circulation, the aorta, and the peripheral arterial tree.