ACE DD Genotype: A Predisposing Factor for Abdominal Aortic Aneurysm

Association of Long-term Use of Antihypertensive Medications With Late Outcomes Among Patients With Aortic Dissection

IMPORTANCE

The associations between long-term treatment of aortic dissection with various medications and late patient outcomes are poorly understood.

OBJECTIVE

To compare late outcomes after long-term use of β-blockers, angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), or other antihypertensive medications (controls) among patients treated for aortic dissection.

DESIGN, SETTING, AND PARTICIPANTS

This population-based retrospective cohort study using the National Health Insurance Research Database in Taiwan included 6978 adult patients with a first-ever aortic dissection who survived to hospital discharge during the period between January 1, 2001, and December 31, 2013, and who received during the first 90 days after discharge a prescription for an ACEI, ARB, β-blocker, or at least 1 other antihypertensive medication. Data analysis was conducted from July 2019 to June 2020.

EXPOSURE

Long-term use of β-blockers, ACEIs, or ARBs, with use of other antihypertensive medications as a control.

MAIN OUTCOMES AND MEASURES

The primary outcomes of interest were all-cause mortality, death due to aortic aneurism or dissection, later aortic operation, major adverse cardiac and cerebrovascular events, hospital readmission, and new-onset dialysis.

RESULTS

Of 6978 total participants, 3492 received a β-blocker, 1729 received an ACEI or ARB, and 1757 received another antihypertension drug. Compared with patients in the other 2 groups, those in the β-blocker group were younger (mean [SD] age, 62.1 [13.9] years vs 68.7 [13.5] years for ACEIs or ARBs and 69.9 [13.8] years for controls) and comprised more male patients (2520 [72.2%] vs 1161 [67.1%] for ACEIs or ARBs and 1224 [69.7%] for controls). The prevalence of medicated hypertension was highest in the ACEI or ARB group (1039 patients [60.1%]), followed by the control group (896 patients [51.0%]), and was lowest in the β-blocker group (1577 patients [45.2%]). Patients who underwent surgery for type A aortic dissection were more likely to be prescribed β-blockers (1134 patients [32.5%]) than an ACEI or ARB (309 patients [17.9%]) or another antihypertension medication (376 patients [21.4%]). After adjusting for multiple propensity scores, there were no significant differences in any of the clinical characteristics among the 3 groups. No differences in the risks for all outcomes were observed between the ACEI or ARB and β-blocker groups. The risk of all-cause hospital readmission was significantly lower in the ACEI or ARB group (subdistribution hazard ratio [HR], 0.92; 95% CI, 0.84-0.997) and β-blocker group (subdistribution HR, 0.87; 95% CI, 0.81-0.94) than in the control group. Moreover, the risk of all-cause mortality was lower in the ACEI or ARB group (HR, 0.79; 95% CI, 0.71-0.89) and the β-blocker group (HR, 0.82; 95% CI, 0.73-0.91) than in the control group. In addition, the risk of all-cause mortality was lower in the ARB group than in the ACEI group (HR, 0.85; 95% CI, 0.76-0.95).

CONCLUSIONS AND RELEVANCE

The use of β-blockers, ACEIs, or ARBs was associated with benefits in the long-term treatment of aortic dissection.

Relationship of genetic factors with development of aortic dissection and aneurysm

Background

This study aims to investigate the relationship between the development of aortic dissections and aneurysms with the polymorphisms of angiotensin converting enzyme gene, methylenetetrahydrofolate reductase gene, plasminogen activator inhibitor-1 gene, and nitric oxide synthase gene.

Methods

Between April 2009 and July 2014, 38 patients with aortic dissections (28 males, 10 females; mean age 55.1±10.7 years; range, 30 to 78 years) and 67 patients with aortic aneurysms (57 males, 10 females; mean age 63.0±11.4 years; range, 31 to 82 years) were included in this cross-sectional study. The control group consisted of 60 healthy volunteers (41 males, 19 females; mean age 56.3±11.2 years; range, 30 to 82 years) without an aortic aneurysm or dissection, as assessed by thoracoabdominal computed tomography. The prespecified four genes were genotyped with competitive allelespecific polymerase chain reaction.

Results

The aortic dissection group had higher nitric oxide synthase-3 (4b/4b) expression levels, compared to the control group. The aortic aneurysm group had also higher nitric oxide synthase-3 (4b/4a) expression levels, compared to the control group. Compared to the control group, a higher rate of angiotensin converting enzyme I/D gene polymorphism was detected in the aneurysm group, while higher D/D polymorphism rates were found in the dissection group; although not statistically significant.

Conclusion

Our study results suggest that the nitric oxide synthase-3 intron 4b/4b and nitric oxide synthase-3 intron 4b/4a gene polymorphisms can be used as a predictor of aortic dissection and aneurysm development.

Abdominal Aortic Aneurysm Genetic Associations: Mostly False? A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND

Many associations between abdominal aortic aneurysm (AAA) and genetic polymorphisms have been reported. It is unclear which are genuine and which may be caused by type 1 errors, biases, and flexible study design. The objectives of the study were to identify associations supported by current evidence and to investigate the effect of study design on reporting associations.

METHODS

Data sources were MEDLINE, Embase, and Web of Science. Reports were dual-reviewed for relevance and inclusion against predefined criteria (studies of genetic polymorphisms and AAA risk). Study characteristics and data were extracted using an agreed tool and reports assessed for quality. Heterogeneity was assessed using I(2) and fixed- and random-effects meta-analyses were conducted for variants that were reported at least twice, if any had reported an association. Strength of evidence was assessed using a standard guideline.

RESULTS

Searches identified 467 unique articles, of which 97 were included. Of 97 studies, 63 reported at least one association. Of 92 studies that conducted multiple tests, only 27% corrected their analyses. In total, 263 genes were investigated, and associations were reported in polymorphisms in 87 genes. Associations in CDKN2BAS, SORT1, LRP1, IL6R, MMP3, AGTR1, ACE, and APOA1 were supported by meta-analyses.

CONCLUSION

Uncorrected multiple testing and flexible study design (particularly testing many inheritance models and subgroups, and failure to check for Hardy-Weinberg equilibrium) contributed to apparently false associations being reported. Heterogeneity, possibly due to the case mix, geographical, temporal, and environmental variation between different studies, was evident. Polymorphisms in nine genes had strong or moderate support on the basis of the literature at this time. Suggestions are made for improving AAA genetics study design and conduct.

An update on the etiology of abdominal aortic aneurysms: implications for future diagnostic testing

Abdominal aortic aneurysm (AAA) disease is multifactorial with both environmental and genetic risk factors. The current research in AAA revolves around genetic profiles and expression studies in both human and animal models. Variants in genes involved in extracellular matrix degradation, inflammation, the renin-angiotensin system, cell growth and proliferation and lipid metabolism have been associated with AAA using a variety of study designs. However, the results have been inconsistent and without a standard animal model for validation. Thus, despite the growing body of knowledge, the specific variants responsible for AAA development, progression and rupture have yet to be determined. This review explores some of the more significant genetic studies to provide an overview of past studies that have influenced the current understanding of AAA etiology. Expanding our understanding of disease pathogenesis will inform research into novel diagnostics and therapeutics and ultimately to improve outcomes for patients with AAA.

Regional changes in elastic fiber organization and transforming growth factor β signaling in aortas from a mouse model of marfan syndrome

In Marfan Syndrome (MFS), development of thoracic aortic aneurysms (TAAs) is characterized by degeneration of the medial layer of the aorta, including fragmentation and loss of elastic fibers, phenotypic changes in the smooth muscle cells, and an increase in the active form of transforming growth factor-β (TGFβ), which is thought to play a major role in development and progression of the aneurysm. We hypothesized that regional difference in elastic fiber fragmentation contributes to TGFβ activation and hence the localization of aneurysm formation. The fibrillin-1-deficient mgR/mgR mouse model of MFS was used to investigate regional changes in elastin fiber fragmentation, TGFβ activation and changes in gene expression as compared to wild-type littermates. Knockdown of Smad 2 and Smad 3 with shRNA was used to determine the role of the specific transcription factors in gene regulation in aortic smooth muscle cells. We show increased elastin fiber fragmentation in the regions associated with aneurysm formation and altered TGFβ signaling in these regions. Differential effects of Smad 2 and Smad 3 were observed in cultured smooth muscle cells by shRNA-mediated knockdown of expression of these transcription factors. Differential signaling through Smad 2 and Smad 3 in regions of active vascular remodeling likely contribute to aneurysm formation in the mgR/mgR model of MFS. Increased elastin fiber fragmentation in these regions is associated with these changes as compared to other regions of the thoracic aorta and may contribute to the changes in TGFβ signaling in these regions.

Adiponectin attenuates abdominal aortic aneurysm formation in hyperlipidemic mice

OBJECTIVE

Abdominal aortic aneurysms (AAA) are age-associated, life-threatening inflammatory dilations of the abdominal aorta. Human population studies have shown an association between obesity and AAA formation, but the molecular mechanisms underlying this connection remain largely unexplored. Adiponectin is an anti-inflammatory adipokine that is downregulated in obesity. In this study we evaluated the role of adiponectin in a model of AAA using apolipoprotein E/adiponectin double-knockout (Apoe(-/-)Apn(-/-)) mice.

APPROACH AND RESULTS

Angiotensin II (Ang II)-infusion in male Apoe(-/-)Apn(-/-) mice led to a higher incidence of AAA and a significant increase of maximal aortic diameter compared with that of Apoe(-/-) mice (2.12 ± 0.07 mm vs. 1.67 ± 0.09 mm, respectively at 28 days). Adiponectin deficiency augmented the early infiltration of macrophages and increased the expression of pro-inflammatory factors in the dilated aortic wall. MMP-2 and MMP-9 activation was also augmented in the aorta of Apoe(-/-)Apn(-/-) mice compared to Apoe(-/-) mice. These data suggest that the downregulation of adiponectin could directly contribute to the elevated incidence of AAA observed in obese individuals.

CONCLUSIONS

Adiponectin attenuates Ang II-induced vascular inflammation and AAA formation in mice.

Analysis of multiple genetic polymorphisms in aggressive-growing and slow-growing abdominal aortic aneurysms

BACKGROUND

The natural history of abdominal aortic aneurysms (AAAs) suggests that some remain slow in growth rate whereas many develop a more accelerated growth rate and reach a threshold for intervention. We hypothesized that different mechanisms are responsible for AAAs that remain slow growing and never become actionable vs the aggressive AAAs that require intervention and may be reflected by distinct associations with genetic polymorphisms.

METHODS

AAA growth rate was determined from serial imaging data in 168 control and 141 AAA patients with ultrasound or computed tomography imaging studies covering ∼5 years. Genetic polymorphisms all previously reported as showing a significant correlation with AAA with functional effects on the expression or function were determined by analysis of the genomic DNA, including angiotensin 1 receptor (rs5186), interleukin-10 (IL-10; rs1800896), methyl-tetrahydrofolate reductase (rs1801133), low-density lipoprotein receptor-related protein 1 (LRP1; rs1466535), angiotensin-converting enzyme (rs1799752), and several matrix metalloproteinase 9 (MMP-9) single nucleotide polymorphisms.

RESULTS

Of the AAA patients, 81 were classified as slow AAA growth rate (<3.25 mm/y) vs 60 with aggressive AAA growth rate (>3.25 mm/y, those presenting with a rupture, or those with maximal aortic diameter >5.5 cm [male] or >5.0 cm [female]). Discriminating confounds between the groups were identified by logistic regression. Analyses identified MMP-9 p-2502 single nucleotide polymorphism (odds ratio [OR], 0.54; 95% confidence interval [CI], 0.31-0.94; P = .029) as a significant confound discriminating between control vs slow-growth AAA, MMP-9 D165N (OR, 0.49; 95% CI, 0.26-0.95; P = .035) and LRP1 (OR, 4.99; 95% CI, 1.13-22.1; P = .034) between control vs aggressive-growth AAAs, and methyltetrahydrofolate reductase (OR, 2.99; 95% CI, 1.01-8.86; P = .048), MMP-9 p-2502 (OR, 2.19; 95% CI, 1.05-4.58; P = .037), and LRP1 (OR, 4.96; 95% CI, 1.03-23.9; P = .046) as the statistically significant confounds distinguishing slow-growth AAAs vs aggressive-growth AAAs.

CONCLUSIONS

Logistic regression identified different genetic confounds for the slow-growth and aggressive-growth AAAs, indicating a potential for different genetic influences on AAAs of distinct aggressiveness. Future logistic regression studies investigating for potential genetic or clinical confounds for this disease should take into account the growth rate and size of the AAA to better identify confounds likely to be associated with aggressive AAAs likely to require intervention.

Associations between the insertion/deletion polymorphism of the angiotensin-converting enzyme and susceptibility to aortic aneurysms: A meta-analysis

INTRODUCTION

The purpose of this study is to examine whether the insertion (I) and deletion (D) polymorphism of the angiotensin-converting enzyme (ACE) confers susceptibility to aortic aneurysms (AAs).

MATERIALS AND METHODS

A meta-analysis was conducted on the associations between the ACE I/D polymorphism and all AAs and abdominal aortic aneurysms (AAAs).

RESULTS

Ten studies consisting of 2784 cases and 2682 controls were available for the meta-analysis. Meta-analysis showed a significant association between the D allele and all types of AA (OR 1.378, 95% CI 1.103-1.723, p = 0.005) and AAA (OR 1.274, 95% CI 1.004-1.617, p = 0.046). Meta-analysis of both the DD genotype and the DD vs. II genotype showed an association with AAAs. Stratification by ethnicity indicated an association between the D allele of the ACE I/D polymorphism and AAAs in Europeans (OR = 1.338, 95% CI = 1.026-1.745, p = 0.031), but not in Asians (OR = 0.927, 95% CI = 0.660-1.303, p = 0.663). Furthermore, analysis using the recessive model, dominant model, and homozygote contrast all showed the same pattern for the D allele.

CONCLUSIONS

Our meta-analysis demonstrates that the ACE I/D polymorphism is associated with susceptibility to AAAs in European populations.

Assessment of insertion/deletion polymorphism of the angiotensin-converting enzyme gene in abdominal aortic aneurysm and inguinal hernia

The aim of the paper is to determine whether the angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism is associated with abdominal aortic aneurysm (AAA) and inguinal hernia. A case-control study was conducted in 264 subjects: 65 patients with AAA, 91 patients with inguinal hernia, 19 patients with both AAA and hernia, and 89 controls were investigated for the ACE I/D polymorphism. Genotype analysis was performed using a polymerase chain reaction technique. Significant differences in the genotype between the patient groups and controls were identified (aneurysm versus control, P = 0.011; aneurysm plus hernia versus control, P = 0.022; hernia versus control, P = 0.001), whereas no differences were found within patient groups. Patients with AAA and/ or hernia had an increased prevalence of I/D heterozygosity, which persisted even after adjusting for differences in confounding clinical variables (aneurysm versus control, OR 0.3, 95% CI 0.2–0.8, P = 0.005; aneurysm plus hernia versus control, OR 0.3, 95% CI 0.1-0.9, P = 0.040; hernia versus control, OR 0.4, 95% CI 0.2–0.7, P = 0.004). In conclusion, an association between the heterozygote ACE I/D state and the presence of AAA and/or hernia was identified. The role of the ACE I/D polymorphism in aneurysm and hernia needs further investigation.

Angiotensin-converting enzyme insertion/deletion polymorphism is a risk factor for thoracic aortic aneurysm in patients with bicuspid or tricuspid aortic valves

OBJECTIVE

The angiotensin-converting enzyme (ACE) is highly expressed in the aneurysmal vascular wall, in both animal models and human disease. Genetic variations in ACE could be crucial in determining the risk of thoracic aortic aneurysm (TAA). The aim of the present study was to examine the role of ACE insertion/deletion polymorphism on the risk of TAA in patients with bicuspid aortic valves or tricuspid aortic valves.

METHODS

We enrolled 216 patients (158 men; age, 58.9±14.9 years) with TAA, associated with bicuspid aortic valves (n=105) and tricuspid aortic valves (n=111) compared with 312 patients (252 men; age, 54.6±11.0 years) with angiographically proven coronary artery disease and 300 healthy controls (91 men; age, 40.4±10.5 years).

RESULTS

The genotype distribution of ACE insertion/deletion was significantly different between the patients with TAA compared with both the control group (P=.0005) and the coronary artery disease group (P=.03). The genotypes were not different between the control group and the coronary artery disease group (P=.3). Compared with the controls, both the bicuspid aortic valve patients (P=.0008) and tricuspid aortic valve patients (P<.0001) had a greater frequency of allele D. The aortic diameters were significantly different among the three genotypes (48.3±6.6, 45.3±8.9, 39.9±8.7 for the DD, DI, and II genotypes, respectively; P=.0002). A synergistic effect between the ACE D allele and hypertension was found for both an increased aortic diameter (P=.003) and the risk of TAA (P<.001). On multivariate logistic regression analysis, D allele (odds ratio, 3.0; 95% confidence interval, 1.1-8.1; P=.03) was a significant predictor of TAA.

CONCLUSIONS

ACE insertion/deletion polymorphism represents a genetic biomarker for TAA. These findings could have a significant effect on both the early detection and effective pharmacologic treatment of aortic disease.

Association between polymorphisms of the renin angiotensin system and carotid stenosis

OBJECTIVE

Carotid stenosis is a common manifestation of systemic atherosclerosis. Apart from traditional risk factors, genetic determinants, such as polymorphisms of the renin angiotensin system (RAS), may be relevant in modulating the atherosclerotic process leading to carotid stenosis. In this study, we investigated the role of angiotensin-converting enzyme (ACE) I/D and -240A>T, angiotensinogen (AGT) M235T, and angiotensin type 1 receptor (AGTR1) 1166A > C polymorphisms in modulating the susceptibility to the disease.

METHODS

Eight hundred twenty-one consecutive patients with severe carotid stenosis (≥70%) and 847 control subjects were investigated.

RESULTS

A significant difference in genotype distribution (P < .0001) and allele frequency (P < .0001) between patients and controls for the ACE I/D polymorphism, but not for the other single-nucleotide polymorphisms investigated, was observed. The ACE D allele frequency was significantly higher in patients without traditional risk factors in comparison with that observed in those with at least one risk factor (0.71 vs 0.61; P = .04). The ACE D allele significantly influenced carotid stenosis under dominant, recessive, and additive model of inheritance at both univariate (P < .0001) and multivariate analysis (P < .0001). When the combined effect of RAS unfavorable alleles was considered, patients carrying less than three alleles had a lower risk of carotid stenosis (odds ratio [OR], 0.79 [0.63-0.99]; P = .05), while carriers of more than four unfavorable alleles had an increased risk (OR, 1.44 [1.12-1.84]; P = .004), in comparison with subjects carrying three or four unfavorable alleles. ACE D allele frequency was similar in patients with and without additional atherosclerotic localizations (0.61 vs 0.62, respectively).

CONCLUSIONS

Our findings evidence a role for ACE I/D polymorphism in influencing the susceptibility to carotid stenosis, even in the absence of traditional risk factors. Interestingly, our findings provided further information concerning the role of this polymorphism in modulating the atherosclerotic process apart from its different localizations.

Impaired abdominal aortic wall integrity in elderly men carrying the angiotensin-converting enzyme D allele

OBJECTIVE

A polymorphism in the angiotensin-converting-enzyme gene (ACE I/D) has been associated with abdominal aortic aneurysm and a link between aortic aneurysm and aortic stiffness has been suggested. This study aimed to explore the links between ACE I/D polymorphism, circulating ACE and abdominal aortic wall integrity as reflected by abdominal aortic wall stiffness.

MATERIAL

A total of 212 men and 194 women, aged 70-88 years, were studied.

METHODS

Mechanical properties of the abdominal aorta were determined using the Wall Track System, ACE genotype using the polymerase chain reaction (PCR) and circulating ACE level by enzyme-linked immunosorbent assay (ELISA).

RESULTS

In men, pulsatile diameter change differed between genotypes (II 0.70, ID 0.55 and DD 0.60 mm, P = 0.048), whereas a tendency was seen for distensibility coefficient (DC) (II 10.38, ID 7.68 and ID 8.79, P = 0.058). Using a dominant model (II vs. ID/DD), men carrying the ACE D allele had lower pulsatile diameter change (P = 0.014) and DC (P = 0.017) than II carriers. Multiple regression analyses showed additional associations between the D allele and increased stiffness β, and reduced compliance coefficient.

CONCLUSION

Men carrying the ACE D allele have stiffer abdominal aortas compared with II carriers. Deranged abdominal aortic stiffness indicates impaired vessel wall integrity, which, along with other local predisposing factors, may be important in aneurysmal disease.

Coding polymorphisms in the genes of the alternative complement pathway and abdominal aortic aneurysm

Variants in the genes of the alternative complement pathway are associated with risk of numerous inflammatory diseases. Abdominal aortic aneurysm is associated with inflammation and is a common cause of illness and death among European populations. This study tested 49 single nucleotide polymorphisms, including common putatively functional polymorphisms, in the genes of the alternative complement cascade (CFH, CFB, CFD, CFI, properdin, CR1, CR1L, CR2, CD46, vitronectin, C3, C5, C6, C7, C8A, C8B, C8G and C9). The study group were 434 cases with infra-renal aortic diameter ≥30 mm and 378 disease-free controls from two UK centres, all with self-reported European ancestry. There was no evidence for significant association with presence or size of aneurysm following correction for multiple testing. This study suggests that variation in the genes of the alternative pathway is not an important cause of abdominal aortic aneurysm development.

Genes and abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a multifactorial disease with a strong genetic component. Since the first candidate gene studies were published 20 years ago, approximately 100 genetic association studies using single nucleotide polymorphisms (SNPs) in biologically relevant genes have been reported on AAA. These studies investigated SNPs in genes of the extracellular matrix, the cardiovascular system, the immune system, and signaling pathways. Very few studies were large enough to draw firm conclusions and very few results could be replicated in another sample set. The more recent unbiased approaches are family-based DNA linkage studies and genome-wide genetic association studies, which have the potential of identifying the genetic basis for AAA, only when appropriately powered and well-characterized large AAA cohorts are used. SNPs associated with AAA have already been identified in these large multicenter studies. One significant association was of a variant in a gene called contactin-3, which is located on chromosome 3p12.3. However, two follow-up studies could not replicate this association. Two other SNPs, which are located on chromosome 9p21 and 9q33, were replicated in other samples. The two genes with the strongest supporting evidence of contribution to the genetic risk for AAA are the CDKN2BAS gene, also known as ANRIL, which encodes an antisense ribonucleic acid that regulates expression of the cyclin-dependent kinase inhibitors CDKN2A and CDKN2B, and DAB2IP, which encodes an inhibitor of cell growth and survival. Functional studies are now needed to establish the mechanisms by which these genes contribute toward AAA pathogenesis.

Group X secretory phospholipase A(2) augments angiotensin II-induced inflammatory responses and abdominal aortic aneurysm formation in apoE-deficient mice

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a complex vascular disease characterized by matrix degradation and inflammation and is a major cause of mortality in older men. Specific interventions that prevent AAA progression remain to be identified. In this study, we tested the hypothesis that Group X secretory phospholipase A(2) (GX sPLA(2)), an enzyme implicated in inflammatory processes, mediates AAA.

METHODS AND RESULTS

GX sPLA(2) was detected by immunostaining in human aneurysmal tissue and in angiotensin II (Ang II)-induced AAAs in apolipoprotein E-deficient (apoE(-/-)) mice. GX sPLA(2) mRNA was increased significantly (11-fold) in abdominal aortas of apoE(-/-) mice in response to Ang II infusion. To define the role of GX sPLA(2) in experimental AAAs, apoE(-/-) and apoE(-/-) x GX sPLA(2)(-/-) (GX DKO) mice were infused with Ang II for either 10 (n=7) or 28 (n=24-26) days. Deficiency of GX sPLA(2) significantly reduced the incidence and severity of AAAs, as assessed by ultrasound measurements in vivo of aortic lumens and by computer-assisted morphometric analyses ex vivo of external diameter. Results from gene expression profiling indicated that the expression of specific matrix metalloproteinases and inflammatory mediators was blunted in aortas from GX DKO mice compared to apoE(-/-) mice after 10-day Ang II infusion. Ang II induction of cyclooxygenase-2, interleukin-6, matrix metalloproteinase (MMP)-2, MMP-13 and MMP-14 was reduced significantly in GX DKO mice compared to apoE(-/-) mice.

CONCLUSION

GX sPLA(2) promotes Ang II-induced pathological responses leading to AAA formation.

Is there an association between angiotensin converting enzyme (ACE) genotypes and abdominal aortic aneurysm?

OBJECTIVES

There is strong evidence of a genetic predisposition to abdominal aortic aneurysm (AAA), however the genes involved remain largely elusive. Recently, two large studies have suggested an association between the angiotensin converting enzyme gene and AAA. This study aimed to investigate the possible association between the ACE insertion/deletion polymorphism and abdominal aortic aneurysm (AAA) in order to replicate the findings of other authors.

DESIGN AND METHODS

A case-control study was performed including 1155 patients with aneurysms and 996 screened control subjects. DNA was extracted from whole blood and genotypes determined in 1155 AAAs and 996 controls using a two stage polymerase chain reaction (PCR) technique.

RESULTS

The groups were reasonably matched in terms of risk factors for AAA. No association was found between the ACE gene insertion/deletion polymorphism and AAA in this study.

CONCLUSIONS

This study cannot support the findings of previous authors and provides evidence against a link between the ACE gene insertion/deletion polymorphism and AAA.

Gene Polymorphisms as Markers of Disease Susceptibility

The most widespread diseases of modern man have a polygenic basis, including genetic predisposition and factors in the external environment. Such is the case with cardiovascular disease, malignancy, diabetes and so on. It should be borne in mind that risk factors usually include disorders that are themselves multifactorial, which further indicates the complexity of pathophysiological mechanisms. In the investigation of genetic factors in polygenic diseases studies are underway to determine the association with specific gene polymorphisms. Genetic or DNA polymorphisms are differences in the hereditary basis which are normally found in human populations. The human genome consists of 3×109nucleotide (base) pairs, and it is considered that, on average, every 1000th nucleotide is polymorphic, i.e. varies between two loci or two individuals. The most common type of gene polymorphisms is the single nucleotide polymorphism (SNP). Although gene polymorphisms are an expression of normal variations in the hereditary basis, their effect on the phenotype is interesting, especially the association with proneness to certain diseases. Association studies examine the incidence of certain genetic variants, i.e. genetic polymorphisms in a group of patients, and compare it with the data of a healthy population. The results are often contradictory, so the number of polymorphisms whose role as markers of genetic predisposition has been clearly confirmed is still small. In this paper we review literature data and present experiences from our laboratory in studying genetic polymorphisms as susceptibility factors for the occurrence of thrombophilia and atherosclerosis and its clinical manifestations.

Abdominal aortic aneurysm: a review of the genetic basis

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex disease with a largely unknown pathophysiological background and a strong genetic component. Various studies have tried to link specific genetic variants with AAA.

METHODS

Systematic review of the literature (1947-2009).

RESULTS

A total of 249 studies were identified, 89 of which were eventually deemed relevant to this review. Genetic variants (polymorphisms) in a wide variety of genes, most of which encode proteolytic enzymes and inflammatory molecules, have been associated with AAA development and progression.

CONCLUSION

The genetic basis of AAA remains unknown, and most results from ''candidate-gene'' association studies are contradictory. Further analyses in appropriately powered studies in large, phenotypically well-characterized populations, including genome-wide association studies, are necessary to elucidate the exact genetic contribution to the pathophysiology of AAA.

The prevalence and clinical impact of obesity in adults with Marfan syndrome

BACKGROUND

Patients with Marfan syndrome characteristically have an asthenic body habitus and are considered to be exempt from the obesity epidemic.

OBJECTIVE

To examine the prevalence and clinical impact of obesity in a cohort of adults with Marfan syndrome.

METHODS

Fifty outpatients (30 female) with a mean (+/- SD) age of 38+/-13 years were studied. Demographic variables including previously identified risk factors for aortic dissection were recorded. Body mass index (BMI) was determined and patients were classified as normal (BMI less than 25 kgm2), overweight (BMI 25 kgm2 to 29.9 kgm2) or obese (BMI 30 kgm2 or greater). Other cardiovascular risk factors were examined. An adverse clinical outcome was defined as either the attainment of surgical criteria for aortic root replacement or the presence of aortic dissection.

RESULTS

A family history of aortic dissection was present in 13 (26%) patients. In 23 (46%) patients, there was no known family history of Marfan syndrome. Mean BMI was 25.4+/-7.4 kgm2, with 18 (36%) patients having an elevated BMI. Positive smoking status was present in 15 (30%), hypertension in 13 (26%) and hyperlipidemia in 19 (38%) patients. Adverse clinical outcome was present in 27 (54%) patients. Logistic regression analysis revealed only index case (OR 44; P<0.001) and higher BMI (OR 1.2; P=0.04) to be significantly and independently associated with increased risk of adverse clinical outcome.

CONCLUSIONS

Obesity is common in adults with Marfan syndrome and is associated with an increased risk of aortic complications.

Genetic and epigenetic mechanisms and their possible role in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a common disease associated with significant cardiovascular morbidity and mortality. The pathogenesis of AAA is poorly defined, making targeting of new therapies problematic. Current evidence favours an interaction of multiple environmental and genetic factors in the initiation and progression of AAA. Epigenetics is the term used to define the properties of the genome that are not explained by the primary sequence, but are due to the modifications of DNA and/or associated proteins. Previous research indicates the association of gene specific promoter DNA hyper-methylation and global DNA hypo-methylation with atherosclerosis. Evidence also suggests an important role for epigenetic processes such as histone acetylation in cardiovascular diseases including atherosclerosis and restenosis. Altered DNA methylation or histone acetylation occur in inflammation, cellular proliferation and remodelling processes and therefore maybe relevant to the pathology of AAA. Important risk factors for AAA, including cigarette smoking, older age, male gender and hypertension, have been linked with epigenetic effects and thus could act in this way to promote AAA. In this review, we discuss the potential role of epigenetic mechanisms in AAA. Since epigenetic alterations are to some extent reversible, further study of this area may identify new treatment targets for AAA.

TGF-beta activity protects against inflammatory aortic aneurysm progression and complications in angiotensin II-infused mice

Complicated abdominal aortic aneurysm (AAA) is a major cause of mortality in elderly men. Ang II-dependent TGF-beta activity promotes aortic aneurysm progression in experimental Marfan syndrome. However, the role of TGF-beta in experimental models of AAA has not been comprehensively assessed. Here, we show that systemic neutralization of TGF-beta activity breaks the resistance of normocholesterolemic C57BL/6 mice to Ang II-induced AAA formation and markedly increases their susceptibility to the disease. These aneurysms displayed a large spectrum of complications on echography, including fissuration, double channel formation, and rupture, leading to death from aneurysm complications. The disease was refractory to inhibition of IFN-gamma, IL-4, IL-6, or TNF-alpha signaling. Genetic deletion of T and B cells or inhibition of the CX3CR1 pathway resulted in partial protection. Interestingly, neutralization of TGF-beta activity enhanced monocyte invasiveness, and monocyte depletion markedly inhibited aneurysm progression and complications. Finally, TGF-beta neutralization increased MMP-12 activity, and MMP-12 deficiency prevented aneurysm rupture. These results clearly identify a critical role for TGF-beta in the taming of the innate immune response and the preservation of vessel integrity in C57BL/6 mice, which contrasts with its reported pathogenic role in Marfan syndrome.

Multilocus analysis in candidate genes ACE, AGT, and AGTR1 and predisposition to peripheral arterial disease: role of ACE D/-240T haplotype

OBJECTIVE

Peripheral arterial disease (PAD) is a common manifestation of systemic atherosclerosis. Apart from traditional cardiovascular risk factors, several novel biologic mediators and genetic predisposing factors appear relevant in determining the atherogenetic process leading to PAD. Genes encoding for renin angiotensin system (RAS) components have been proposed as candidate in atherosclerosis. This study investigated four polymorphisms in angiotensinogen (AGT), angiotensin converting enzyme (ACE), and angiotensin II receptor type 1 (AGTR1), genes of RAS, in both predicting PAD and modulating the severity of the disease.

METHODS

The ACE I/D and -240A>T, AGT M235T, and AGTR1 1166A>C polymorphisms were analyzed in 281 PAD patients and in 485 controls comparable for age and sex.

RESULTS

The ACE D and -240T alleles both significantly influenced the predisposition to PAD. The ACE D, but not -240 T, allele remained associated with PAD after Bonferroni correction (P = .004) and adjustment for cardiovascular risk factors (P = .03). The ACE D allele influenced PAD predisposition with a dose-dependent effect (odds ratio for ACE ID vs II genotype, 1.77; P = .006; ACE DD vs II genotype, 2.15; P = .001). The haplotype reconstruction analysis for the ACE gene showed that the D/-240T haplotype significantly and independently influenced the predisposition to PAD (P = .02). In 190 PAD patients with no additional atherosclerotic localizations (isolated PAD), a significant association between ACE D and -240T alleles and PAD was observed. Only the ACE D allele remained associated with isolated PAD after Bonferroni correction (P = .02) and after adjustment for cardiovascular risk factors (P = .02). The haplotype reconstruction analysis for the ACE gene showed that the D/-240T, but not the D/-240A haplotype significantly influenced the predisposition to PAD (P = .0003). No influence of the polymorphisms analyzed on the severity of the disease, according to Rutherford categories, was found.

CONCLUSIONS

The present study contributes data to highlight the role of the ACED/-240T haplotype in predisposing to PAD, also in the absence of other atherosclerotic comorbidities.

Interferon-gamma and the interferon-inducible chemokine CXCL10 protect against aneurysm formation and rupture

BACKGROUND

Vascular disease can manifest as stenotic plaques or ectatic aneurysms, although the mechanisms culminating in these divergent disease manifestations remain poorly understood. T-helper type 1 cytokines, including interferon-gamma and CXCL10, have been strongly implicated in atherosclerotic plaque development.

METHODS AND RESULTS

Here, we specifically examined their role in the formation of abdominal aortic aneurysms in the angiotensin II-induced murine model. Unexpectedly, we found increased suprarenal aortic diameters, abdominal aortic aneurysm incidence, and aneurysmal death in apolipoprotein E- and interferon-gamma-deficient (Apoe(-/-)/Ifng(-/-)) mice compared with Apoe(-/-) controls, although atherosclerotic luminal plaque formation was attenuated. The interferon-gamma-inducible T-cell chemoattractant CXCL10 was highly induced by angiotensin II infusion in Apoe(-/-) mice, but this induction was markedly attenuated in Apoe(-/-)/Ifng(-/-) mice. Apoe(-/-)/Cxcl10(-/-) mice had decreased luminal plaque but also increased aortic size, worse morphological grades of aneurysms, and a higher incidence of death due to aortic rupture than Apoe(-/-) controls. Furthermore, abdominal aortic aneurysms in Apoe(-/-)/Cxcl10(-/-) mice were enriched for non-T-helper type 1-related signals, including transforming growth factor-beta1. Treatment of Apoe(-/-)/Cxcl10(-/-) mice with anti-transforming growth factor-beta neutralizing antibody diminished angiotensin II-induced aortic dilation.

CONCLUSIONS

The present study defines a novel pathway in which interferon-gamma and its effector, CXCL10, contribute to divergent pathways in abdominal aortic aneurysm versus plaque formation, inhibiting the former pathology but promoting the latter. Thus, efforts to develop antiinflammatory strategies for atherosclerosis must carefully consider potential effects on all manifestations of vascular disease.

Lack of association between angiotensin-converting enzyme gene polymorphism and type I aortic dissection

The relationship between angiotensin-converting enzyme (ACE) gene polymorphism and type I aortic dissection was examined in 205 unrelated hypertensives. A total of 94 patients underwent emergency repair due to type I aortic dissection, confirmed by computed tomography, and the remaining 111 were controls. Polymerase chain reaction was used to confirm that ACE gene polymorphism was due to insertion (I) or deletion (D) of a 287 base pair (bp) DNA sequence within intron 16. The genotype distribution and allele frequency of ACE I/D polymorphism between patients and controls were not statistically significant. When the frequency of at least one D allele carrier (DD or ID genotype) was compared with the II homozygous genotype, there was also no significant difference between the study groups. The findings revealed no association between ACE I/D polymorphism and aortic dissection. We conclude that I/D mutation of the ACE gene does not seem to be a risk factor for aortic dissection.

ACE and TGFBR1 genes interact in influencing the susceptibility to abdominal aortic aneurysm

A role of ACE I/D polymorphism in the pathogenesis of abdominal aortic aneurysm (AAA) has been demonstrated, possibly due to the effect of angiotensin II on vascular tissue remodelling. Angiotensin II exerts profibrogenic effects through the local induction of TGF-beta. Dysregulated TGF-beta signalling may result from mutations in TGFBR1 and TGFBR2 genes, thus resulting in degenerative changes in the vessel wall. We performed a case-control study in order to investigate the role of TGFBR1 9A6A polymorphism as predisposing factor to AAA per se, and in the presence of ACE DD and AT1R 1166 CC genotypes in 201 AAA patients (mean age+/-S.D., 71.5+/-6.9) referred to the Unit of Vascular Surgery of the University of Florence, compared with 252 healthy controls (mean age+/-S.D., 70.6+/-8.6). A significant difference in genotype distribution and allele frequency between patients and controls was found for ACE, but not for AT1R and TGFBR1 polymorphisms. At univariate analysis a significant association between ACE DD, but not AT1R CC and TGFBR1 6A allele, and the susceptibility to the disease was found [ACE DD OR=1.86 (95% CI 1.26-2.76), p=0.002]. After adjustment for age, gender, traditional cardiovascular risk factors, and CAD, PAD and CVD, ACE DD genotype still affected the susceptibility to AAA [OR=2.13 (95% CI 1.06-4.28), p=0.03], and the contemporary presence of ACE DD genotype and TGFBR1 6A allele, increased the predisposition to the disease [OR=5.09 (95% CI 1.44-18.02), p=0.01]. This study, which demonstrates an interaction between ACE and TGFBR1 genes in predisposing to AAA, may provide further information on the mechanisms contributing to AAA susceptibility, and offer a topic for future larger studies.

The role of the renin-angiotensin system in aortic aneurysmal diseases

The renin-angiotensin system has been invoked in the development of both abdominal and thoracic aortic aneurysms. This has been demonstrated experimentally by the chronic subcutaneous infusion of angiotensin II, which consistently leads to development of abdominal aortic aneurysms (AAAs) in mice. Angiotensin II-induced AAAs have highly heterogenous cellular and extracellular matrix characteristics throughout the aorta that change markedly with infusion duration. The mechanistic basis for the reproducible location of AAA development has not been elucidated, but many insights have been provided, especially regarding receptor and inflammatory mechanisms. A recent clinical study provided limited evidence for extrapolating these results to mechanisms of human AAAs. Experimental evidence has also demonstrated that antagonism of angiotensin II type 1 (AT1) receptors prevents ascending aortic aneurysms in a murine model of Marfan's syndrome. A clinical study is currently ongoing to demonstrate the efficacy of AT1 receptor antagonism in humans.

Tissue inhibitor of metalloproteinase-1 (TIMP-1) polymorphisms in a Caucasian population with abdominal aortic aneurysm

BACKGROUND

The formation of a sporadic abdominal aortic aneurysm (AAA) is explained by the remodeling of the extracellular matrix (ECM) and breakdown of structural components of the vascular wall. Matrix metalloproteinases are the principal matrix-degrading proteases and are known to play a major role in the remodeling of the extracellular matrix in arterial vessels. Their activity is controlled by tissue inhibitors of metalloproteinases (TIMPs). Decreased TIMP-1 and TIMP-2 expression in the extracellular matrix of the walls of AAAs has been shown in several studies. This case control study was designed to investigate the possible impact of genetic variants of the TIMP-1 gene in the etiology of AAA.

METHODS

TIMP-1 single nucleotide polymorphisms (SNPs) were analyzed in a primary study sample of 50 patients with AAA and 44 controls. Differences in genotype and allele frequencies of identified polymorphisms were determined after sequencing the entire coding region and selected parts of the promoter using the automated laser fluorescence technique. A second sample (96 patients vs. 89 controls) was investigated by single-base sequencing to confirm significant results.

RESULTS

Three polymorphisms were identified, one of which, described for the first time in this article, is located in intron 4 (TIMP-1: 328 + 16C > T). A statistically significant difference in allele frequencies for SNP TIMP-1 372T>C was detected in the primary study group. The C allele was more frequent in male patients with AAA than in the control group [23 vs. 4, p = 0.029, OR (95% CI) 4.38 (1.13-20.47)]. However, this result could not be confirmed in a second sample of males [52 vs. 45, p = 0.624, OR (95% CI) 1.16 (0.65-2.06)]. There were no statistically significant differences in genotype or allele frequencies of the other detected SNPs between the two groups.

CONCLUSIONS

Our analysis of the entire coding region and selected parts of the promoter of the TIMP-1 gene failed to show an association between genetic polymorphisms and AAA, suggesting that variations in the TIMP-1 gene do not contribute to the development of AAA.

Angiotensin II type 1 receptor 1166C polymorphism is associated with abdominal aortic aneurysm in three independent cohorts

OBJECTIVE

Although polymorphic variations in genes of the RAS system have previously been associated with susceptibility to AAA, such studies have been significantly limited by small sample sizes. This study was undertaken, using the largest case series yet reported, to determine whether common genetic variants of the RAS are associated with either susceptibility or severity of AAA.

METHODS AND RESULTS

The frequencies of 4 common genetic variants of genes related to the renin-angiotensin system were investigated in 3 geographically distinct, but ethnically similar, case-control cohorts, resulting in comparison of 1226 AAA cases with 1723 controls. In all 3 the AGTR1 1166C allele was significantly more common in AAA patients than controls (overall adjusted OR 1.60, 95% CI 1.32 to 1.93, P=1.1x10(-6)). Overall, the ACE ID genotype was associated with AAA (OR 1.33, 95% CI 1.06 to 1.67, P<0.02). The AGT 268T allele appeared to have an epistatic effect on large aneurysm size.

CONCLUSIONS

This study has identified a strong and repeated association between the AGTR1 1166C allele and susceptibility to AAA, and a weaker effect associated with the ACE deletion allele, in 3 geographically distinct, but ethnically similar, case-control cohorts. This study highlights the key role of the RAS in AAA and emphasizes the need for replication and validation of results in suitable independent cohorts.

The interleukin-10-1082 'A' allele and abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysms (AAA) are caused by inflammatory processes in the wall of the aorta resulting in degradation of structural proteins. This inflammatory process is mediated, in part, by cytokines, and interleukin-10 (IL-10) is a predominantly anti-inflammatory cytokine. A single nucleotide polymorphism in the promoter region of the IL-10 gene that affects transcription has been associated with AAA in a small study. The aim of this study was to determine whether this polymorphism is associated with AAA and also examine its effect on the growth of small AAA.

METHODS AND RESULTS

A case control study was performed. A total of 389 patients with AAA and 404 healthy controls were recruited. IL-10-1082 polymorphisms were determined by polymerase chain reaction-based methods. In the case of patients with small AAA (<5.5 cm), serial size measurements were recorded to determine mean growth rate. There was a statistically significant difference both in allele and genotype frequencies between the case and control groups with the IL-10-1082 'A' allele being more common in the AAA group (P = .006). In the AAA group, genotype frequencies were as follows: GG 84, GA 201, and AA 104. In the control group, the genotype frequencies were GG 118, GA 205, and AA 81. The odds ratio for the 'A' allele as a risk factor for AAA was 1.50 (95% confidence interval 1.09 to 2.07). Regression modeling revealed that the IL-10-1082 genotype was, however, not independently associated with AAA if age, tobacco use, hypertension, and history of coronary or peripheral artery disease was taken into account. There was a trend towards lower plasma IL-10 level in IL-10 AA carriers, but the IL-10 'A' allele did not have any discernible effect on the growth of small AAA.

CONCLUSIONS

This study demonstrates that the IL-10-1082 'A' allele is associated with AAA, although this association is likely to be secondary to an association between IL-10-1082 genotype and other markers of cardiovascular disease rather than AAA per se.

Traditional and novel risk factors for clinically diagnosed abdominal aortic aneurysm: the Kaiser multiphasic health checkup cohort study

BACKGROUND

Identification of risk factors for and early diagnosis of clinically significant abdominal aortic aneurysm (AAA) before rupture is vital to optimize outcomes in these patients. Our aim was to examine traditional and three novel potential risk factors (abdominal obesity, white blood cell count, and kidney function) for abdominal aortic aneurysm (AAA, comprising discharge diagnosis or surgical repair) in a large multiethnic population.

METHODS

Cohort study (N =104,813) conducted at an integrated health care delivery system in northern California.

RESULTS

After a median of 13 years, 605 AAA events (490 in men and 115 in women; 91 [15%] fatal) were observed. In multivariable analysis, factors significantly associated with risk of clinically detected AAA included male gender, older age, black race (inversely), low educational attainment, cigarette smoking (with dose-response relation), height, treated and untreated hypertension, high total serum cholesterol, elevated white blood cell count, known coronary artery disease, history of intermittent claudication, and reduced kidney function. A significant Asian race by gender interaction was found such that Asian race had a (borderline significant) protective association with AAA in men but not in women.

CONCLUSIONS

Our findings confirm that major atherosclerotic risk factors, except for diabetes and obesity, are also prospectively related to AAA and suggest that elevated white blood cell count and reduced kidney function may improve risk stratification for clinically relevant AAA.

The Genetic Basis of Abdominal Aortic Aneurysms: A Review

INTRODUCTION

The pathogenesis of abdominal aortic aneurysm (AAA) remains poorly understood, however significant evidence has emerged in recent years to suggest a chronic inflammatory process. Observational studies have highlighted a familial trend towards AAA development among relatives of affected individuals and it is thought that inflammatory genes may influence an individual's susceptibility. Conflicting reports exist over single gene versus multiple gene inheritance patterns in addition to a collection of studies examining individual inflammatory genes. This paper reviews the evidence for a genetic predisposition to aneurysm formation including familial and segregation studies in addition to experimental evidence investigating specific candidate genes.

METHOD

Medline and Pubmed database searches were conducted using the search terms abdominal aortic aneurysm and gene. Papers were reviewed and references manually searched for further relevant publications which were added to the data. Papers were categorised under the headings familial, segregation and candidate gene studies.

RESULTS

A review of 58 papers is presented under sub-headings as above. In the case of the candidate gene section, a brief report of the functional relevance of each gene is included.

CONCLUSION

A summary of the evidence presented is given and the direction of future work in this field is briefly considered.

Role of the renin-angiotensin system in the development of abdominal aortic aneurysms in animals and humans

The mediators for the initiation, progression, and rupture of abdominal aortic aneurysms (AAAs) have not been defined. Recent evidence has demonstrated that chronic infusion of angiotensin II via subcutaneously placed osmotic pumps can reproducibly form AAAs in mice. The evolution of AngII-induced AAAs in these mice is complex. Rapid medial macrophage accumulation precedes transmedial breaks and large lumen expansion, which are restricted to the suprarenal aorta. After this initial phase, there is a more gradual rate of lumen expansion that is progressive with continued AngII exposure. There is extensive aortic remodeling during this gradual expansion phase. An initial prominent thrombus gradually resolves and is replaced by fibrous tissue containing several types of inflammatory cells. At prolonged intervals of AngII infusion, internal aortic diameters of the suprarenal aorta can increase up to fourfold compared to the same region in saline-infused mice. The extrapolation of these data in mice to the development of human AAAs remains to be determined. However, there are a considerable number of drugs available to potentially test the efficacy of inhibiting the renin-angiotensin system on the progression of the human disease.

Abdominal Aortic Aneurysm as a Complex Multifactorial Disease: Interactions of Polymorphisms of Inflammatory Genes, Features of Autoimmunity, and Current Status of MMPs

The role of matrix metalloproteinases (MMPs) in the pathogenesis of abdominal aortic aneurysm (AAA) has focused on the degradation of the extracellular matrix (ECM). The new frontier of MMP biology involves the role of MMPs in releasing cryptic fragments and neoepitopes from the ECM and the impact of MMPs on the regulation of the inflammatory response. The ECM is a complex structure, much more important than an inert scaffold. Both MMP-2 and MMP-9 expose a cryptic epitope that controls angiogenesis. MMPs inhibit angiogenesis through the release of endostatin, endorepellin, arresten, canstatin, and tumstatin. Other breakdown products of the ECM include fragments of fragmin and elastin degradation products (EDPs). In addition, the ECM contains embedded vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-beta). Inflammation is a complex, highly regulated system that involves the identification of injury or infection, response to the injury or infection, repair and healing, and return to normal homeostasis. In some instances, the inflammatory process leads to a pathologic process that is damaging to the host. MMPs play an important role in the control of the inflammatory response through the modification of proinflammatory cytokines, chemokines, and shedding of membrane receptors. Genetic association studies have been performed to help determine the genetic risk associated with certain single nucleotide polymorphisms (SNPs) However, because of the variability in the patient populations and the size of the population, it is difficult to draw any conclusions from these studies. While the etiology of AAA remains unknown, understanding of the inflammatory process and its regulatory points will develop new strategies for the treatment of AAA. Perhaps one difficulty with understanding the pathogenesis of AAA is the lack of precise definition of the phenotype.

Abdominal aortic aneurysm: pathogenesis and implications for management

Abdominal aortic aneurysm (AAA) affects approximately 5% of elderly men and is responsible for a significant number of deaths in Western Countries. At present surgery by open or endovascular means is the only widely used therapy for this condition. In this review we examine the risk factors, serum, and genetic associations of AAA. Epidemiology studies suggest that smoking cessation and control of cholesterol and blood pressure should reduce the number of patients developing AAA. Natural history studies suggest that smoking cessation should reduce the rate of progression of AAA. Clear level 1 evidence for drug treatments of AAA are presently lacking; however, animal and human in vitro studies suggest that medication targeted at reducing inflammation and proteolysis are most likely to be beneficial, with limited data to support the use of statins, Angiotensin II inhibitors, and macrolides. Work has commenced in understanding which patients, identified by clinical, serum, and genotype, are more at risk of AAA progression and thus should be selected out for aggressive treatment. Well designed large multicenter randomized controlled trials are required to examine the medical treatment of AAA.

Angiotensin-converting enzyme inhibitors and aortic rupture: a population-based case-control study

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors prevent the expansion and rupture of aortic aneurysms in animals. We investigated the association between ACE inhibitors and rupture in patients with abdominal aortic aneurysms.

METHODS

We did a population-based case-control study of linked administrative databases in Ontario, Canada. The sample included consecutive patients older than 65 (n=15,326) admitted to hospital with a primary diagnosis of ruptured or intact abdominal aortic aneurysm between April 1, 1992, and April 1, 2002.

FINDINGS

Patients who received ACE inhibitors before admission were significantly less likely to present with ruptured aneurysm (odds ratio [OR] 0.82, 95% CI 0.74-0.90) than those who did not receive ACE inhibitors. Adjustment for demographic characteristics, risk factors for rupture, comorbidities, contraindications to ACE inhibitors, measures of health-care use, and aneurysm screening yielded similar results (0.83, 0.73-0.95). Consistent findings were noted in subgroups at high risk of rupture, including patients older than 75 years and those with a history of hypertension. Conversely, such protective associations were not observed for beta blockers (1.02, 0.89-1.17), calcium channel blockers (1.01, 0.89-1.14), alpha blockers (1.15, 0.86-1.54), angiotensin receptor blockers (1.24, 0.71-2.18), or thiazide diuretics (0.91, 0.78-1.07).

INTERPRETATION

ACE inhibitors are associated with a reduced risk of ruptured abdominal aortic aneurysm, unlike other antihypertensive agents. Randomised trials of ACE inhibitors for prevention of aortic rupture might be warranted.

Angiotensin-Converting Enzyme in Systemic Sclerosis: From Endothelial Injury to a Genetic Polymorphism

The main pathologic hallmark of systemic sclerosis (SSc) is endothelial derangement; the pathologic alterations of the vessel wall in SSc are strikingly similar to the modification detected in the atherosclerotic lesions, and it is now evident that SSc is also characterized by accelerated macrovascular disease. Peptides related to angiotensin II, the final product of the renin-angiotensin system (RAS), play a role as regulators of endothelial cell function. Angiotensin-converting enzyme (ACE), the key enzyme in the RAS, is the predominant pathway of angiotensin II formation in blood and tissues. In intron 16 of the gene encoding for ACE an insertion/deletion (I/D) polymorphism, consisting of the presence or absence of a 287-base pair Alu sequence, has been identified. This polymorphism has been related to ACE enzyme levels, and data from experimental studies reported a functional role for this polymorphism in modulating the angiotensin II levels. We previously documented a high ACE D allele frequency in SSc patients and its role in increasing the risk of SSc, thus suggesting that the I/D polymorphism might be a useful genetic marker to identify SSc patients at risk to develop a severe vascular disease, frequently leading to gangrene. Moreover, our preliminary data, besides supporting the role of ACE I/D polymorphism as a predisposing factor to SSc, demonstrated its involvement in accelerated macrovascular disease by increasing the intima media thickness. Therefore, in SSc, not only endothelial dysfunction, but also vascular damage, linked to ACE I/D polymorphism, may significantly contribute to accelerated macrovascular disease, as the ACE D allele, by regulating both the production of angiotensin II and the degradation of bradykinin, contributes to mechanisms involved in the induction and maintenance of vessel wall modification.