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

Autoantigenicity of carbonic anhydrase 1 in patients with abdominal aortic aneurysm, revealed by proteomic surveillance

Abdominal aortic aneurysm (AAA) is sometimes detected in patients with atherosclerosis. One of the histological characteristics of AAA walls is infiltration of inflammatory cells, in which autoimmunity may be involved. Thereby, we here surveyed autoantigens in AAA walls by proteomics. Specifically, we separated proteins extracted from AAA wall samples by 2-dimensional electrophoresis and detected candidate autoantigens by western blotting. One of the detected candidates was carbonic anhydrase 1 (CA1). ELISA confirmed that the autoantibodies to CA1 were detected more frequently in AAA patients (n=13) than in healthy donors (n=25) (p=0.03). Interestingly, some serum samples from the AAA patients reacted to CA1 of the AAA walls stronger than to CA1 of peripheral blood mononuclear cells from healthy donors. Our data indicate that CA1 in the AAA walls would be modified to express neo-epitope(s) and that the autoimmunity to CA1 may be involved in the pathogenesis of AAA.

[Infrarenal aortic ectasia in retroperitoneal fibrosis (RPF)]

We analysed the infrarenal aortic morphology by abdominal MR-examinations of 47 RPF patients compared to a control group. A significant larger aortic calibre and higher rates of infrarenal dilatation in male RPF patients were observed. The larger aortic diameter in male RPF patients may be due to periaortic inflammation with resulting aortic ectasia and supports the classification of RPF into the spectrum of chronic periaortitis.

Association between human parainfluenza virus type 1 and smoking history in patients with an abdominal aortic aneurysm

Several studies have suggested that infectious agents may induce the development of abdominal aortic aneurysms and/or accelerate their progression. The aim of this study was to evaluate the presence of the respiratory-transmitted viruses such as influenza A and B and parainfluenza type 1 genomes in bioptic fragments of abdominal aortic aneurysms. Furthermore, the association between viral infection and traditional risk factors for aneurysms was investigated employing multivariate logistic regression models. The genome of parainfluenza 1 was detected in 11 out of 57 patients with abdominal aortic aneurysm, influenza A only in one, whereas none of the specimens analyzed resulted positive for influenza B. After adjustment of age, gender, and clinical diagnosis, being current smokers was associated independently with parainfluenza 1 detection in aneurysms. The identification of parainfluenza 1 in aortic aneurysm biopsies supports previous observations of a possible role of viruses in the lesion development. Smoking, by interfering with the respiratory tract's ability to defend itself and predisposing to upper and lower respiratory tract infections may accelerate the onset and progression of abdominal aortic aneurysms.

Endothelial and smooth muscle cells from abdominal aortic aneurysm have increased oxidative stress and telomere attrition

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex multi-factorial disease with life-threatening complications. AAA is typically asymptomatic and its rupture is associated with high mortality rate. Both environmental and genetic risk factors are involved in AAA pathogenesis. Aim of this study was to investigate telomere length (TL) and oxidative DNA damage in paired blood lymphocytes, aortic endothelial cells (EC), vascular smooth muscle cells (VSMC), and epidermal cells from patients with AAA in comparison with matched controls.

METHODS

TL was assessed using a modification of quantitative (Q)-FISH in combination with immunofluorescence for CD31 or α-smooth muscle actin to detect EC and VSMC, respectively. Oxidative DNA damage was investigated by immunofluorescence staining for 7, 8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG).

RESULTS AND CONCLUSIONS

Telomeres were found to be significantly shortened in EC, VSMC, keratinocytes and blood lymphocytes from AAA patients compared to matched controls. 8-oxo-dG immunoreactivity, indicative of oxidative DNA damage, was detected at higher levels in all of the above cell types from AAA patients compared to matched controls. Increased DNA double strand breaks were detected in AAA patients vs controls by nuclear staining for γ-H2AX histone. There was statistically significant inverse correlation between TL and accumulation of oxidative DNA damage in blood lymphocytes from AAA patients. This study shows for the first time that EC and VSMC from AAA have shortened telomeres and oxidative DNA damage. Similar findings were obtained with circulating lymphocytes and keratinocytes, indicating the systemic nature of the disease. Potential translational implications of these findings are discussed.

Abdominal aortic aneurysm and abdominal wall hernia as manifestations of a connective tissue disorder

BACKGROUND

Abdominal aortic aneurysms (AAAs) and abdominal wall hernias represent chronic degenerative conditions. Both aortic aneurysms and inguinal hernias share common epidemiologic features, and several investigators have found an increased propensity for hernia development in patients treated for aortic aneurysms. Chronic inflammation and dysregulation in connective tissue metabolism constitute underlying biological processes, whereas genetic influences appear to be independently associated with both disease states. A literature review was conducted to identify all published evidence correlating aneurysms and hernias to a common pathology.

METHODS

PubMed/Medline was searched for studies investigating the clinical, biochemical, and genetic associations of AAAs and abdominal wall hernias. The literature was searched using the MeSH terms "aortic aneurysm, abdominal," "hernia, inguinal," "hernia, ventral," "collagen," "connective tissue," "matrix metalloproteinases," and "genetics" in all possible combinations. An evaluation, analysis, and critical overview of current clinical data and pathogenic mechanisms suggesting an association between aneurysms and hernias were undertaken.

RESULTS

Ample evidence lending support to the clinical correlation between AAAs and abdominal wall hernias exists. Pooled analysis demonstrated that patients undergoing aortic aneurysm repair through a midline abdominal incision have a 2.9-fold increased risk of developing a postoperative incisional hernia compared with patients treated for aortoiliac occlusive disease (odds ratio, 2.86; 95% confidence interval, 1.97-4.16; P < .00001), whereas the risk of inguinal hernia was 2.3 (odds ratio, 2.30; 95% confidence interval, 1.52-3.48; P < .0001). Emerging evidence has identified inguinal hernia as an independent risk factor for aneurysm development. Although mechanisms of extracellular matrix remodeling and the imbalance between connective tissue degrading enzymes and their inhibitors instigating inflammatory responses have separately been described for both disease states, comparative studies investigating these biological processes in aneurysm and hernia populations are scarce. A genetic predisposition has been documented in familial and observational segregation studies; however, the pertinent literature lacks sufficient supporting evidence for a common genetic basis for aneurysm and hernia.

CONCLUSIONS

Insufficient data are currently available to support a systemic connective tissue defect affecting the structural integrity of the aortic and abdominal wall. Future investigations may elucidate obscure aspects of aneurysm and hernia pathophysiology and create novel targets for pharmaceutical and gene strategies for disease prevention and treatment.

Quantification and location of Chlamydia pneumoniae-specific antigen in the walls of abdominal aortic aneurysms

BACKGROUND

To evaluate the prevalence and quantity of Chlamydia pneumoniae-specific antigen in the three layers (intima, media, and adventitia) of abdominal aortic aneurysms (AAAs), so as to further investigate the pathogenesis of AAAs.

METHODS

Aortic walls were collected from 20 patients with AAA and 11 healthy organ donors. Immunohistochemistry was used to identify the C pneumoniae-specific antigen, and image analysis system was used to quantify and locate it.

RESULTS

The positive rate of C pneumoniae-specific antigen was higher in the AAA group than in the control group (100% vs. 54.54%, p = 0.003), positive intensity decreased from the tunica intima to the adventitia in the AAA group (16.32% ± 2.13%, 14.84% ± 1.80%, and 14.25% ± 1.67%, respectively, p = 0.003). In the control group, positive cells were mainly found in focal lesion areas.

CONCLUSION

We have demonstrated the presence and differentiation of C pneumoniae-specific antigen in the three layers of AAAs, which are in accordance with pathology, thus suggesting a pathogenic role of the antigen.

Current status of medical management for abdominal aortic aneurysm

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

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.

Overexpression of interleukin-1β and interferon-γ in type I thoracic aortic dissections and ascending thoracic aortic aneurysms: possible correlation with matrix metalloproteinase-9 expression and apoptosis of aortic media cells

OBJECTIVE

To examine the expression of interleukin-1β and interferon-γ and their possible roles in aortic dissections and aneurysms.

METHODS

Aortic specimens were obtained from patients with type I thoracic aortic dissection, ascending thoracic aortic aneurysms, and control organ donors. The expression of interleukin-1β, interferon-γ, matrix metalloproteinase-9, and signal transduction factors phospho-p38 and phosphorylated c-jun N-terminal kinase (phospho-JNK) were detected by real time reverse transcription-polymerase chain reaction (real time RT-PCR), Western blot, and immunohistochemistry, respectively. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining was performed to detect apoptosis of media cells. The correlation of these factors and apoptosis was also studied.

RESULTS

Apoptosis in the media of thoracic aortic dissection and in ascending thoracic aortic aneurysms was dramatically higher than in the control group. The expression of interleukin-1β gradually increased from the control group, thoracic aortic dissection to ascending thoracic aortic aneurysms (p < 0.01, respectively). The expression of interferon-γ and matrix metalloproteinase-9 was significantly increased in the media of thoracic aortic dissection and ascending thoracic aortic aneurysms compared with the control group (p < 0.01, respectively). There were positive correlations between interleukin-1β versus matrix metalloproteinase-9, interleukin-1β versus phospho-p38 in thoracic aortic dissection (p < 0.01, respectively), and interferon-γ versus matrix metalloproteinase-9, interferon-γ versus phospho-JNK, interferon-γ versus apoptosis, and interleukin-1β versus apoptosis in ascending thoracic aortic aneurysms (p = 0.02, 0.02, p < 0.01, p < 0.01).

CONCLUSIONS

Interleukin-1β and interferon-γ might effect the formation of thoracic aortic dissection and ascending thoracic aortic aneurysms possibly through the up-regulation of matrix metalloproteinase-9 and the apoptosis of media cells in humans.

Inflammation and immune response in acute aortic dissection

OBJECTIVE

The aim of our study was to evaluate the lymphocyte subpopulations and the cytokines in the peripheral blood of patients with type-A Stanford acute aortic dissection (AAD group) and to determine whether inflammatory cells are present at the site of aortic dissection.

METHODS

Thirty-five consecutive patients with type-A Stanford dissection were evaluated for haemochrome and lymphocyte subpopulations (CD3+, CD4+, CD8+, CD19+, CD4+CD25+, CD16+CD56+, CD4+CD28-, CD8+CD28-) by flow cytometry. C-reactive protein (CRP), tumour necrosis factor (TNF)-α, interleukin (IL)-2, IL-4, IL-6, IL-8, IL-10, interferon-gamma (IFN-γ), and monocyte chemoattractant protein (MCP)-1 were measured by ELISA. In addition, immunohistochemical staining with cell type-specific antibodies was performed to study the inflammatory cells detected inside the aortic wall.

RESULTS

In the AAD group, a significant increase in natural killer (NK) (P = 0.032), B cells (P = 0.022), and CD8+CD28- (P = 0.045) subpopulations was observed, whereas there was a significant decrease in total T lymphocytes (P = 0.004) and T helper fractions (P = 0.005). Moreover, a significant increase in CRP (P < 0.0001), IL-6 (P < 0.0001), IL-8 (P < 0.0001), IL-10 (P < 0.0001), TNF-α (P < 0.0001), and MCP-1 (P < 0.001) was observed; macrophages represented the main population detected inside the media.

CONCLUSIONS

Our results strongly support the hypothesis of a pivotal role of innate immunity in type-A Stanford AAD.

In Vivo Study on the Expression Pattern of Resistin in Patients With Abdominal Aortic Aneurysm

Objective: To study the expression pattern of resistin in abdominal aortic aneurysms and to correlate its plasma levels to aneurysm size and statin therapy. Patients and Methods: From 25 patients on regular and 38 patients without statin therapy tissue specimen and plasma samples were obtained for analysis. Results: Demographic data, past medical history, and body mass index showed no significant differences between the statin and no statin group. Immunohistochemistry showed positive stainings for resistin in all sections and in part colocalization to CD 68 positive cells. Patients with large aneurysms showed significant correlation of C-reactive protein (CRP) and interleukin 10 (IL-10) levels; patients on statin medication had significantly lower plasma levels of resistin and CRP. Conclusion: In contrast to IL-10 and CRP plasma levels of resistin are not correlated to aneurysm diameter; yet statin therapy results in decrease of resistin and CRP, suggesting an anti-inflammatory action in patients with abdominal aortic aneurysms (AAAs).

Persistent Chlamydophila pneumoniae infection in thoracic aortic aneurysm and aortic dissection?

OBJECTIVES

Chlamydophila pneumoniae (C. pneumoniae) has been associated with atherosclerosis and abdominal aortic aneurysm and is probably disseminated by peripheral blood mononuclear cells (PBMC). Viable and metabolically active bacteria can be demonstrated by the presence of bacterial mRNA and on-going dissemination by the presence of bacteria in PBMC. The aim of this study was to determine the prevalence of C. pneumoniae DNA and mRNA in aortic biopsies and C. pneumoniae DNA in PBMC in thoracic aortic aneurysm and aortic dissection patients.

DESIGN

Real-time PCR was used to detect C. pneumoniae DNA and mRNA in biopsies and C. pneumoniae DNA in PBMC.

RESULTS

C. pneumoniae DNA was found in biopsies in 26% (6/23) of aneurysm patients and 11% (2/18) of dissection patients but in none of the forensic autopsy controls. C. pneumoniae mRNA was not found in any biopsy, and all PBMC were C. pneumoniae-negative.

CONCLUSIONS

Presence of C. pneumoniae DNA but not mRNA in aortic biopsies and no evidence of C. pneumoniae in PBMC suggest that the infection in the aorta has passed into a state of persistence.

The Influence of Diabetes on Degree of Abdominal Aortic Aneurysm Tissue Inflammation

Abdominal aortic aneurysm (AAA) progression and disease resistance are related to transmural degenerative processes and an inflammatory infiltration (INF). Diabetes is associated with low prevalence and growth rate of AAA. We sought to characterize INF in established AAA (INFAAA), in diabetic patients. From 89 male patients aged 52 to 83 years, aneurysm specimens obtained at open asymptomatic nonruptured AAA repair were graded for INF and immunostained using antibodies against T-lymphocytes (CD3) and macrophages (CD68). Diabetic patients had an odds ratio (OR) 3.8, 95% confidence interval ([CI] 1.14-12.96), P = .03, of experiencing above-median INFAAA. These associations were affected by serum glucose (SG) levels (OR 3.6, 95% CI [0.72-18.77]; P = .1). Macrophage subpopulations higher in diabetic patients (1.44 ± 0.78 versus 0.98 ± 0.76; P = .02) were correlated with SG (r = .21, P = .044). Abdominal aortic aneurysms in diabetic patients are associated with higher INF. Macrophage densities are correlated with SG.

High Levels of Endothelin (ET)-1 and Aneurysm Diameter Independently Predict Growth of Stable Abdominal Aortic Aneurysms

The etiology of abdominal aortic aneurysm (AAA) includes inflammation and endothelial dysfunction. To evaluate relations between these mechanisms and AAA growth, endothelin (ET)-1, tumor necrosis factor (TNF)-α, interleukin (IL)-6, and CD40 ligand were related to yearly AAA growth for 2.9 ± 1.6 years (mean ± SD) in 178 patients with conservatively followed AAA. Total number of follow-up years was 491. Abdominal aortic aneurysm diameter increased by 3.3 ± 4.0 mm during the first year and by 4.9 ± 4.4 mm during the first 2 years. Median (range) growth was 2.5 (—1.0 to 30.6) mm/year. When patients with AAA growth above or below median were compared, initial AAA diameter (46.1 ± 5.8 vs 42.0 ± 8.3 mm; P < .0001), age (75 ± 7 vs 72 ± 8 years; P < .029), and initial ET-1 levels (1.31 ± 0.50 vs 1.13 ± 0.49 pg/mL; P < .0177) were higher in patients with growth above median. Endothelin 1 (P = .0230) and initial AAA diameter (P = .0019) predicted AAA growth above median in logistic regression. In conclusion, higher initial levels of ET-1 and initial AAA diameter independently predict AAA growth.

Increased metabolic activity in abdominal aortic aneurysm detected by 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT)

OBJECTIVES

Abdominal aortic aneurysms (AAAs) are associated with an inflammatory cell infiltrate and enzymatic degradation of the vessel wall. The aim of this study was to detect increased metabolic activity in the wall of the AAA with 18F-fluorodeoxyglucose ((18)F-FDG), mediated by glucose transporter protein (GLUTs), using a dedicated hybrid PET/64-detector CT. DESIGN, METHOD AND MATERIALS: 14 patients (All male, mean age 73.6 years, range 61-82) with AAA under surveillance underwent PET/CT scanning with 175 MBq of intravenous (18)F-FDG. The maximum aneurysm diameter and calcification score were determined on the attenuation correction CT. A volume of interest was placed on the aneurysm sac and the maximum Standardised Uptake Value (SUV(max)) measured.

RESULTS

The mean aneurysm diameter was 5.4 cm (SD+/-0.8). Two aneurysms had the CT characteristics of inflammatory aneurysms. Twelve aneurysms showed increased FDG uptake (SUV(max)>2.5). There was no significant difference in FDG uptake between heavily calcified aneurysms and non-heavily calcified aneurysms (t-test). There was a significant increase in the FDG uptake in the two inflammatory aneurysms compared to the other twelve aneurysms (t-test; P=0.04).

CONCLUSION

The findings in this study offer in vivo evidence that the AAA wall shows increased glucose metabolism, mediated by the GLUTs: this increased metabolic activity as detected by PET/CT may be present in most AAAs.

Chlamydial lipopolysaccharide (cLPS) is present in atherosclerotic and aneurysmal arterial wall--cLPS levels depend on disease manifestation

BACKGROUND

The role of Chlamydia pneumoniae in peripheral atherosclerosis disease and abdominal aortic aneurysm (AAA) remains unclear. Chlamydial lipopolysaccharide (cLPS) detection is a method used conventionally in routine chlamydial diagnosis of gynecological or ophthalmic samples.

METHODS

We compared cLPS concentrations, as well as other markers of bacterial load, in plaques and sera of patients operated on for carotid artery stenosis (n=110), aorto-occlusive disease (n=22), or AAAs (n=50) at the Helsinki University Central Hospital.

RESULTS

The median levels of cLPS in plaques were 2.28, 0.80, and 0.29 ng/ml in AAA, aorto-occlusive disease, and carotid artery stenosis patients, respectively (P<.001, Kruskal-Wallis). cLPS in serum correlated with LPS binding protein levels (Spearman's rho=0.52, P<.001), suggesting that the presence of chlamydiae is sufficient to produce an innate immune response reaction in these patients. Serum inflammatory markers interleukin 6 and highly sensitive C-reactive protein also correlate with cLPS (Spearman's rho=0.42 and 0.51, respectively, P<.001).

CONCLUSIONS

cLPS is present in arterial disease, and the potential role of C. pneumoniae in the pathogenesis of both peripheral atherosclerosis disease and AAA should not be forgotten. cLPS has a positive correlation with serum inflammatory markers, but this is no proof of a causal association.

Thoracic aortic aneurysm patients with Chlamydophila pneumoniae infection showed a shift in trace element levels in serum and diseased aortic tissue

Few studies have been performed on trace elements in tissues and serum in cardiovascular disease and none in aortic aneurysm. In this study the concentrations of 10 trace elements were determined in serum and aneurysmatic aortic tissue from 23 patients undergoing thoracic surgery. Macroscopically, normal thoracic aortic tissue specimens from 10 forensic autopsies and serum from 23 healthy blood donors served as controls. DNA from the intracellular respiratory pathogen Chlamydophila pneumoniae (C. pneumoniae), which may be involved in the pathogenesis of atherosclerosis, was found in 26% (6/23) of the patients but in none of the controls. The serum copper/zinc ratio, a well-known marker of ongoing infection and/or inflammation, was higher (26%, p<0.001) in aneurysm patients. C. pneumoniae requires iron for its growth. In our aneurysm patients iron was higher in serum (by 54%, p<0.001) and aneurysmal tissue (by 60%, p<0.001). Although calcium was lower in patient sera (by 8%, p<0.001), it tended to be higher (by 20%, ns) in aneurysmatic tissue. In addition, mercury concentrations in serum and aneurysmatic tissue were positively correlated (r=0.51, p<0.05). Moreover, C. pneumoniae-positive aneurysmatic tissues had lower concentrations of manganese (46%, p<0.05) and zinc (26%, ns) but a higher concentration of mercury (50%, p<0.05) than C. pneumoniae-negative aneurysmatic tissues. In conclusion, aneurysm patients showed a shift in trace element levels in serum and in the diseased part of the aorta, the pattern being partly different in C. pneumoniae-positive compared with C. pneumoniae-negative patients. The results are compatible with active infection and/or inflammation, possibly initiated by C. pneumoniae.

Inflammatory response is associated with aortic dissection

Aortic dissection is an age-dependent life-threatening cardiovascular disease with high mortality rates. Recent research has shown that inflammation plays an important role in aortic dissection. Inflammatory cells, such as lymphocytes and macrophages, not only increase the expression of proteases and cell adhesion molecules but also release reactive oxygen species. These cells also contribute to apoptosis of smooth muscle cells in the aortic artery, and finally lead to medial degradation. This process has been considered to be the principal mechanism for aortic dissection. Furthermore, changes in systemic inflammatory biomarkers are associated with acute-phase reactions and complications in aortic dissection. These biomarkers are also used to predict the prognosis of aortic dissection and to distinguish acute aortic dissection from other chest pain diseases. In addition, elevated inflammatory cell activity in aortic wall, identified by positron emission tomography/computed tomography, is associated with serious clinical symptoms and leads to a poor clinical outcome in aortic dissection. Such observations may provide us with new sights into the mechanism of aortic dissection. In this review, we discuss the role of inflammation in the development and progression of aortic dissection. Understanding this inflammatory process may provide us with new strategies for pharmacological treatment of aortic dissection.

An overview of cytokine interactions in atherosclerosis and implications for peripheral arterial disease

Over the last three decades, a surge in research into the inflammatory pathophysiology of atherosclerosis has highlighted an array of cytokines and other inflammatory mediators associated with underlying inflammatory burden. The ability to identify and simultaneously measure multiple cytokines in peripheral blood highlights their potential as biomarkers of atherosclerosis. This has prompted much research in vascular medicine to identify the ;at-risk' groups for atherostenotic or atheroaneurysmal disease. This review is compiled with similar intentions and aims to discern the relevant evidence for cytokine profiling in peripheral arterial disease (PAD), where such information is lacking, while providing a holistic overview of cytokine interactions in atherosclerosis. This is pertinent given that cytokine profiles from coronary artery disease and aortic aneurysm studies cannot be directly extrapolated to PAD due to differences in inflammatory environments that exist in these conditions. Whilst plaque morphology and blood rheology play an important role in the cardiac manifestations of atherosclerosis, tissue thrombogenecity is very important in PAD. Further, cytokines act in concert rather than in isolation in a disease process, and no single cytokine in a cross-sectional model is able to serve as an absolute screening marker. Thus, it is essential to understand the regulation of cytokine production in atherosclerosis prior to evaluating the viability and merits of a multimarker approach for clinical risk stratification in PAD.

Effect of statins on proteolytic activity in the wall of abdominal aortic aneurysms

BACKGROUND

The aim of this study was to examine the effect of statin treatment on the activity of proteases in the wall of abdominal aortic aneurysms (AAAs).

METHODS

The activities of matrix metalloproteinases (MMPs) 9 and 3, cathepsins B, H, K, L and S, and the cystatin C level were measured in extracts of AAA wall taken from 82 patients undergoing AAA repair; 21 patients were receiving statin treatment before surgery. All values were standardized against soluble protein (SP) concentration in the extract, and reported as median (interquartile range) or mean(s.e.m.).

RESULTS

The two groups had similar demographics. Reduced activity of MMP-9 (43 (34-56) versus 80 (62-110) pg per mg SP; P < 0.001), cathepsin H (183 (117-366) versus 321 (172-644) nmol 4-methylcoumarin-7-amide released per mg SP; P = 0.016) and cathepsin L (102 (51-372) versus 287 (112-816) micromol 7-amino-4-trifluoromethylcoumarin released per mg SP; P = 0.020) was found in the statin-treated aortas compared with AAAs from patients not taking a statin. The statin-treated group had lower MMP-3 activity, but this did not reach statistical significance (P = 0.053). Cystatin C levels were higher in statin-treated aortas than in controls (41.3(3.1) versus 28.9(2.1) ng per mg SP; P = 0.003).

CONCLUSION

Statins decreased the activity of proteases that have been implicated in aneurysm disease.

Dilation-dependent activation of platelets and prothrombin in human thoracic ascending aortic aneurysm

OBJECTIVE

The purpose of this study was to investigate whether thoracic ascending aortic aneurysm (TAAA) induces platelet activation as mural thrombus participates in aortic dilatation in abdominal aortic aneurysm and TAAA are associated with rheological factors favoring coagulation activation.

METHODS AND RESULTS

We studied the relation between coagulation activation and aortic diameter in Marfan patients (MFS) with various aortic diameters (n=52). We then studied patients presenting large aneurysms associated with bicuspid aortic valve (BAV) and degenerative form. Lastly, we used immunochemistry and biochemistry to investigate prothrombin/thrombin retention within the aortic wall. Microparticles, sGPV, tissue factor, and TAT complexes were increased in plasma from MFS with large aneurysms (>or=45 mm) compared to MFS with limited aortic dilatation (<45 mm). Similar elevations were observed in all patients with large aortic aneurysms, regardless of the etiology, the site of maximal aortic dilation, associated valvulopathy, risk factors, or treatments. P-selectin and platelet-bound fibrinogen were also increased, demonstrating platelet activation in large aneurysms. Significant increase in sCD146 plasma concentration suggested alteration of endothelium.

CONCLUSIONS

Platelet activation occurs in patients with large aneurysms of the ascending aorta, is dependent on aortic dilation, and is associated with thrombin generation, part of which appears to be retained in mucoid degeneration areas.

Cysteine protease activity in the wall of abdominal aortic aneurysms

BACKGROUND

Cysteine proteases are potent elastolytic enzymes and together with their inhibitor, cystatin C, have been linked with the growth of abdominal aortic aneurysms (AAAs). These enzymes and their inhibitors have previously been studied in AAAs, but comparisons have always been made with wall from normal aorta. Atherosclerosis is a feature of aneurysmal disease and may therefore confound comparisons with normal wall. This study compared the expression and activity of cysteine proteases and their inhibitors in aneurysm wall with their expression in the aortic wall of patients with aortic occlusive disease (AOD).

METHODS

Aortic wall was obtained from 82 patients with AAA and 13 with AOD. Protein expression and activity of cathepsin B, H, K, L and S, and cystatins A, B, and C were measured by enzyme-linked immunosorbent assay and specific fluorogenic substrate assays. Matrix metalloproteinase 9 (MMP-9) activity was measured by quantitative bioimmunoassay in the same extracts.

RESULTS

AAA wall had 330% more cathepsin H protein (P = .007) and >30% less cystatin C (P = .03) than the aortic wall from patients with AOD. The activity of cathepsins B, H, L, and S was significantly greater in AAA than AOD (376%, [P < .0001], 191%, [P = 0.019], 223%, P = 0.002, and approximately 20% [P = 0.045] respectively). MMP-9 activity was also increased in AAA compared with AOD (P<0.0001) and levels in the wall of AAA correlated positively with cathepsin L activity (r = 0.42, P<.0001) and negatively with cystatin C (r = -0.75, P<.0001).

CONCLUSIONS

The activity of four cathepsins B, H, L, and S was higher in the aneurysm wall than in aortic wall of patients with occlusive disease. This was associated with a reduced level of cystatin C in the aneurysmal wall. Cathepsin H was the only protein in which there was a correlation between protein level and activity, which suggests that post-translational modifications were responsible for activation of the other cathepsins. Increased cathepsin activity may influence the activity of MMP-9, which is thought to have an important role in aneurysm development.

Polymorphisms of the interleukin-6 gene promoter and abdominal aortic aneurysm

BACKGROUND

Elevated levels of circulating interleukin-6 (IL-6) have been reported in patients with abdominal aortic aneurysms (AAAs). Although this implicates inflammation as a cause of AAAs, there is also evidence that the aneurysmal aorta may secrete IL-6 into the circulation as a result of aortic proteolysis. Genetic association studies are one means of trying to clarify the role of specific mediators in the causal pathway. The aim of the present study was to examine the association between variants of the IL-6 gene and AAAs.

METHODS

An association study involving 677 men with screen-detected AAAs and 656 age-matched controls was performed. Three variants in the IL-6 promoter region were analysed: IL-6-174G>C (rs1800795), IL-6-572G>C (rs1800796) and IL-6-597G>A (rs1800797). Univariate regression of SNP genotype on AAA as a binary outcome was initially performed under a range of genetic models (additive, dominant and recessive). This was followed by multivariate analyses, testing the same models but including risk factors known to be associated with AAAs. All analyses and haplotype estimation were performed under a generalized linear model framework.

RESULTS

IL-6-572G>C polymorphism (frequency 1.5% in cases) was identified as an independent risk factor for AAA with an odds ratio (OR) of 6.00 (95%CI: 1.22, 29.41) when applied to the recessive model. No association was seen in the additive or dominant models. In a multivariate analysis using the most common haplotype (h.111, frequency 48.7%) as a reference, h.211 (frequency 4.4%) was an independent risk factor for AAA (OR 1.56, 95%CI: 1.02, 2.39).

CONCLUSION

The IL-6 572G>C polymorphism (and h.211 haplotype) is associated with AAA, however it is too rare to be an important cause of most AAAs. This does not support the concept that the elevated level of IL-6 reported in patients with AAAs is a primary cause of the aneurysmal process.

Lack of microbial DNA in tissue specimens of patients with abdominal aortic aneurysms and positive Chlamydiales serology

In a case-control study that included a total of 98 patients and 83 controls, the possible link between various pathogens and abdominal aortic aneurysms was investigated. For 68 patients with abdominal aortic aneurysm and age-matched controls, no differences were detected in the levels of immunoglobulin (Ig)A and IgG Chlamydiaceae and Chlamydophila pneumoniae antibodies. Patients with IgA titers positive for Chlamydophila pneumoniae showed progressive disease (defined as an annual increase of the aneurysm diameter of > or = 0.5 cm) more frequently than patients with negative IgA titers (p = 0.046). Polymerase chain reactions performed to detect DNA for Chlamydophila pneumoniae, Chlamydia trachomatis, Chlamydophila psittaci, human cytomegalovirus, Borrelia burgdorferi and Helicobacter pylori in tissue specimens of 30 patients and 15 controls were negative. In summary, Chlamydophila pneumoniae may contribute to aortic aneurysm disease progression, but DNA of this and other pathogens was not found in patients' specimens.

Abdominal aortic aneurysm is a specific antigen-driven T cell disease

To determine whether monoclonal/oligoclonal T cells are present in abdominal aortic aneurysm (AAA) lesions, we amplified beta-chain T cell receptor (TCR) transcripts from these lesions by the nonpalindromic adaptor (NPA)-polymerase chain reaction (PCR)/V-beta-specific PCR followed by cloning and sequencing. Sequence analysis revealed the presence of substantial proportions of identical beta-chain TCR transcripts in AAA lesions in 9 of 10 patients examined, strongly suggesting the presence of oligoclonal populations of alphabeta TCR+ T cells. We have also shown the presence of oligoclonal populations of gammadelta TCR+ T cells in AAA lesions. Sequence analysis after appropriate PCR amplification and cloning revealed the presence of substantial proportions of identical VgammaI and VgammaII TCR transcripts in 15 of 15 patients examined, and of Vdelta1 and Vdelta2 TCR transcripts in 12 of 12 patients. These clonal expansions were very strong. All these clonal expansions were statistically significant by the binomial distribution. In other studies, we determined that mononuclear cells infiltrating AAA lesions express early- (CD69), intermediate- (CD25, CD38), and late- (CD45RO, HLA class II) activation antigens. These findings suggest that active ongoing inflammation is present in the aortic wall of patients with AAA. These results demonstrate that oligoclonal alphabeta TCR+ and gammadelta TCR+T cells are present in AAA lesions. These oligoclonal T cells have been clonally expanded in vivo in response to yet unidentified antigens. Although the antigenic specificity of these T cells remains to be determined, these T cells may play a significant role in the initiation and/or the propagation of the AAA. It appears that AAA is a specific antigen-driven T cell disease.

Bacterial diversity in aortic aneurysms determined by 16S ribosomal RNA gene analysis

BACKGROUND

Aortic aneurysms are common vascular conditions that cause considerable morbidity and mortality. Understanding of the mechanisms involved in the pathogenesis of the condition remains limited. Recently, infection has been suggested as possible contributor in the development of the disease. The aim of the present study was to examine aortic aneurysms for the presence of bacterial DNA using polymerase chain reaction (PCR) targeting the 16S ribosomal RNA (rRNA) gene, followed by cloning and sequencing.

METHODS

Universal eubacterial primers were used to amplify 16S rRNA bacterial genes in 10 specimens from arterial walls of aortic aneurysms. Subsequently, PCR amplicons were cloned into Escherichia coli and sequencing of the cloned inserts was used to determine species identity or closest relatives by comparison with known sequences in GenBank.

RESULTS

Sequences of Stenotrophomonas spp., including S. maltophilia (formerly Pseudomonas homology group V) were detected in six aneurysm samples. Propionibacterium acnes was identified in five samples, and Brevundimonas diminuta (formerly P. diminuta) in four samples. Other species previously assigned to the Pseudomonas genus such as Comamonas testosteroni, Delftia acidovorans, Burkholderia cepacia, Herbaspirillum sp., and Acidovorax sp. were also detected. Some clones fell into other environmental species, including Methylobacterium sp. and Bradyrhizobium elkanii, and others represented bacteria that have not yet been cultivated. DNA sequences from oral bacteria, including Streptococcus sanguinis, Tannerella forsythia, and Leptotrichia buccalis were detected. Sequences from Prevotella melaninogenica and Lactobacillus delbrueckii, which are commonly found in both mouth and gastrointestinal tract, were also detected. Additional species included Dermacoccus spp. and Corynebacterium vitaeruminis.

CONCLUSIONS

A wide variety of bacteria, including oral bacteria, was found to colonize aortic aneurysms and may play a role in their development. Several of these microorganisms have not yet been cultivated.

CLINICAL RELEVANCE

Although Chlamydophila pneumoniae has been detected in aneurysmal walls, its exact role in the condition remains inconclusive. Overall, there is scarce information about the role of microorganisms in aneurysmal disease. In the present study, we used molecular genetics to detect a diversity of bacteria in arterial walls of aortic aneurysms. The presence of multiple microorganisms in aneurysmal disease may have implications for chemoprophylaxis and antibiotic treatment if directed only at C.pneumoniae.

99m Tc-Annexin-V Functional Imaging of Luminal Thrombus Activity in Abdominal Aortic Aneurysms

Background— The mural thrombus of abdominal aortic aneurysms (AAA) is involved in aneurysm progression via several interdependent biological processes including platelet activation. 99m Tc-annexin V (ANX) is a scintigraphic tracer that binds to phosphatidylserine exposed on activated platelets and apoptotic cells. Here, we evaluated the potential of ANX imaging to assess mural thrombus biological activity in an experimental AAA model. The clinical applicability was further tested ex vivo on human samples of excised AAA thrombi.

Methods and Results— Experimental AAA was created by infusing elastase into infrarenal abdominal aorta in 17 rats, and 6 sham-operated rats were used as controls. Abdominal ANX scintigraphy was performed 2 weeks later followed by quantitative autoradiography and histological studies. Among the 13 rats which developed AAA, 11 displayed intense ANX uptake within AAA by scintigraphy. ANX uptake in the aneurysms on planar and single-photon emission computed tomography (SPECT) imaging was higher than that observed in infrarenal aorta of sham-operated controls (target/background ratio: 5.7±0.9 versus 1.33±0.21; P <0.005 for SPECT). Aneurysm-to-background activity ratios obtained by scintigraphy correlated with ANX activity in corresponding autoradiograms ( R =0.69; P <0.02). This activity was located in the thrombus area where activated platelets and polymorphonuclear leukocytes accumulated. Similar patterns were also found in all of the 7 human AAA thrombi harvested during surgery.

Conclusions— ANX imaging may assess mural thrombus renewal activity linked to permanent flowing blood interface.