The Role of Chlamydia Pneumoniae in Human Aortic Disease—A Hypothesis Revisited

Human abdominal aortic aneurysm (AAA): Evidence for an autoimmune antigen-driven disease

Abdominal aortic aneurism (AAA) is a complex immunological disease with a strong genetic component, and one of the ten leading causes of death of individuals 55-74 years old worldwide. Strong evidence has been accumulated suggesting that AAA is an autoimmune specific antigen-driven disease. Mononuclear cells infiltrating AAA lesions comprised of T and B lymphocytes and other cells expressing early-, intermediate- and late-activation antigens, and the presence of antigen-presenting cells have been documented, demonstrating an ongoing immune response. The three components of the trimolecular complex, T-cell receptor (TCR)/peptide (antigen)/HLA have been identified in AAA, and specifically: (i) clonal expansions of T-cell clones in AAA lesions; (ii) the association of AAA with particular HLA Class I and Class II; and (iii) self or nonself putative AAA-associated antigens. IgG autoantibodies recognizing proteins present in normal aortic tissue have been reported in patients with AAA. Molecular mimicry, defined as the sharing of antigenic epitopes between microorganisms (bacteria, viruses) and self antigens, maybe is responsible for T-cell responses and antibody production in AAA. Also, the frequency and the suppressor activity of CD4 + CD25 + FOXP3+ Tregs and the expression of FOXP3 transcripts and protein have been reported to be significantly impaired in AAA patients vs normal donors.

Risk reduction and pharmacological strategies to prevent progression of aortic aneurysms

INTRODUCTION

While size thresholds exist to determine when aortic aneurysms warrant surgical intervention, there is no consensus on how best to treat this disease before aneurysms reach the threshold for intervention. Since a landmark study in 1994 first suggested ß-blockers may be useful in preventing aortic aneurysm growth, there has been a surge in research investigating different pharmacologic therapies for aortic aneurysms - with very mixed results.

AREAS COVERED

We have reviewed the existing literature on medical therapies used for thoracic and abdominal aortic aneurysms in humans. These include ß-blockers, angiotensin II receptor blockers, and angiotensin-converting enzyme inhibitors as well as miscellaneous drugs such as tetracyclines, macrolides, statins, and anti-platelet medications.

EXPERT OPINION

While multiple classes of drugs have been explored for risk reduction in aneurysm disease, with few exceptions results have been disappointing with an abundance of contradictory findings. The vast majority of studies have been done in patients with abdominal aortic aneurysms or thoracic aortic aneurysm patients with Marfan Syndrome. There exists a striking gap in the literature when it comes to pharmacologic management of non-Marfan Syndrome patients with thoracic aortic aneurysms. Given the differences in pathogenesis, this is an important future direction for aortic aneurysm research.

Pathophysiological Aspects of the Development of Abdominal Aortic Aneurysm with a Special Focus on Mitochondrial Dysfunction and Genetic Associations

Abdominal aortic aneurysm (AAA) is a complex degenerative vascular disease, with considerable morbidity and mortality rates among the elderly population. The mortality of AAA is related to aneurysm expansion (the enlargement of the aortic diameter up to 30 mm and above) and the subsequent rupture. The pathogenesis of AAA involves several biological processes, including aortic mural inflammation, oxidative stress, vascular smooth muscle cell apoptosis, elastin depletion, and degradation of the extracellular matrix. Mitochondrial dysfunction was also found to be associated with AAA formation. The evidence accumulated to date supports a close relationship between environmental and genetic factors in AAA initiation and progression. However, a comprehensive pathophysiological understanding of AAA formation remains incomplete. The open surgical repair of AAA is the only therapeutic option currently available, while a specific pharmacotherapy is still awaited. Therefore, there is a great need to clarify pathophysiological cellular and molecular mechanisms underlying AAA formation that would help to develop effective pharmacological therapies. In this review, pathophysiological aspects of AAA development with a special focus on mitochondrial dysfunction and genetic associations were discussed.

Association of Chlamydia pneumoniae Infection With Atherosclerotic Plaque Formation

Atherosclerosis is a complex multifactorial disorder. Studies show that infectious microbial agents may play an important role in the development of atherosclerosis; however, these findings are conflicting. This study investigated the presence of Chlamydia pneumoniae DNA in atherosclerotic plaques of patients suffering from coronary artery disease. In a cross-sectional study, 85 patients (43 females and 42 males with mean age of 61±9.5, range 42-82 years) referred for coronary artery bypass grafting (CABG) and thoracic biopsy as the control groups were enrolled for this study. Standard questionnaires, including demographic and clinical evaluation were administered. Obtained specimens were processed and then nested polymerase chain reaction with primers for Pst1 fragment was carried out to detect Chlamydia pneumoniae DNA. Statistical analysis was done using the SPSS software. Of note, in 25 out of the 85 patients (29.4%), C. pneumoniae was detected within atherosclerotic plaques, whereas, 5 out of the 85 thoracic biopsy (5.9%) were positive for the presence of the mentioned bacteria in internal thoracic artery. There was a statistically significant association between atherosclerotic plaque (study group) and thoracic biopsy (control group) in terms of C. pneumoniae positivity (P=0.0001). The findings of this study support the hypothesis that C. pneumoniae is associated with atherosclerosis.

Porphyromonas gingivalis participates in pathogenesis of human abdominal aortic aneurysm by neutrophil activation. Proof of concept in rats

Background

Abdominal Aortic Aneurysms (AAAs) represent a particular form of atherothrombosis where neutrophil proteolytic activity plays a major role. We postulated that neutrophil recruitment and activation participating in AAA growth may originate in part from repeated episodes of periodontal bacteremia.

Methods and Findings

Our results show that neutrophil activation in human AAA was associated with Neutrophil Extracellular Trap (NET) formation in the IntraLuminal Thrombus, leading to the release of cell-free DNA. Human AAA samples were shown to contain bacterial DNA with high frequency (11/16), and in particular that of Porphyromonas gingivalis (Pg), the most prevalent pathogen involved in chronic periodontitis, a common form of periodontal disease. Both DNA reflecting the presence of NETs and antibodies to Pg were found to be increased in plasma of patients with AAA. Using a rat model of AAA, we demonstrated that repeated injection of Pg fostered aneurysm development, associated with pathological characteristics similar to those observed in humans, such as the persistence of a neutrophil-rich luminal thrombus, not observed in saline-injected rats in which a healing process was observed.

Conclusions

Thus, the control of periodontal disease may represent a therapeutic target to limit human AAA progression.

IgG4-related inflammatory abdominal aortic aneurysm

PURPOSE OF REVIEW

IgG4-related systemic disease is a recently proposed entity characterized by high serum IgG4 concentrations, sclerosing inflammation containing numerous IgG4-positive plasmacytes, dramatic responsiveness to steroid therapy, and occurrence of multiple organs. This review described that some cases of inflammatory abdominal aortic aneurysm (IAAA) have similar clinicopathological features that are now considered to represent aortic lesions of IgG4-related systemic disease under the concept of IgG4-related IAAA.

RECENT FINDINGS

IgG4-related IAAA is characterized by high serum IgG4 and immunoglobulin E levels, high titers of antinuclear antibodies, and high prevalence of allergic disorders such as bronchial asthma. The patients show a risk of developing IgG4-related systemic diseases in other organs during their life. Histologically, sclerosing inflammation containing numerous IgG4-positive plasmacytes is observed predominantly in the adventitia. Similar lesions have also been reported in the thoracic aorta and large arteries.

SUMMARY

Recognition of the fact that IgG4-related systemic disease could involve the vascular lesions offers potential new management of those. However, only 3 years have passed since the first report of IgG4-related IAAA. Further studies are necessary to elucidate other vascular lesions associated with IgG4-related systemic disease, the usefulness of steroid therapy for the management of IgG4-IAAA, and underlying pathological and immunological characteristics.

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.

Recent advances in molecular mechanisms of abdominal aortic aneurysm formation

Abdominal aortic aneurysm (AAA) is an increasingly common clinical condition with fatal implications. It is associated with advanced age, male gender, cigarette smoking, atherosclerosis, hypertension, and genetic predisposition. Although significant evidence has emerged in the last decade, the molecular mechanisms of AAA formation remain poorly understood. Currently, the treatment for AAA remains primarily surgical with the lone innovation of endovascular therapy. With advances in the human genome, understanding precisely which molecules and genes mediate AAA development and blocking their activity at the molecular level could lead to important new discoveries and therapies. This review summarizes recent updates in molecular mechanisms of AAA formation, including animal models, autoimmune components, infection, key molecules and cytokines, mechanical forces, genetics, and pharmacotherapy. This review will be helpful to those who want to recognize the newest endeavors within the field and identify possible lines of investigation in AAA.

Detection by broad-range real-time PCR assay of Chlamydia species infecting human and animals

BACKGROUND

Tests available for molecular diagnosis of chlamydial infections detect Chlamydiatrachomatis, but do not find other Chlamydia species associated with genital, ophthalmic, cardiovascular, respiratory or neurological diseases. The routine detection of all Chlamydia species would improve the prognosis of infected people and guide therapeutic choices.

AIM

To design and validate a sensitive, specific, reproducible, inexpensive and easy-to-perform assay to quantify most Chlamydia species.

METHODS

Primers and probe were selected using the gene coding for the 16S rRNA. The detection limits were assessed for suspensions of Chlamydia trachomatis, Chlamydia psittaci and Chlamydia pneumoniae. The performance of this test was compared with that of two commercial kits (Amplicor-Roche and Artus) on 100 samples obtained from children with trachoma.

RESULTS

The detection capacities for Chlamydia trachomatis of the broad-range real-time polymerase chain reaction (PCR) were similar or slightly better than those obtained with commercial kits (0.2 copies of DNA/microl). Only the broad-range PCR identified specimens containing Chlamydia psittaci and Chlamydia pneumoniae. The commercial kits and the broad-range assay detected Chlamydia species in 5% and in 11%, respectively, of samples from children with trachoma.

CONCLUSIONS

This new real-time PCR offers a sensitive, reproducible assay that produces results in <3 h. With panels of quantified Chlamydia species, this real-time PCR can be run with all real-time PCR equipment. Larger trials are needed to confirm the utility of this test in diagnosis and for therapeutic follow-up.

Detection of C. pneumoniae by polymerase chain reaction-enzyme immunoassay in abdominal aortic aneurysm walls and its association with rupture

OBJECTIVE

Serological studies have suggested that one of the risk factors for aneurysm development is C. pneumoniae infection. The purpose of this study was to evaluate whether there is an association between the presence of C. pneumoniae DNA in aneurysms and ruptured abdominal aortic aneurysms.

METHODS

Aortic walls were collected consecutively from 30 patients with intact AAA, 16 patients with ruptured AAA and 19 healthy organ donors (control). Purified DNAs from all aortas were analyzed for the presence of C. pneumoniae DNA in parallel by polymerase chain reaction-enzyme immunoassay (PCR-EIA) and agarose gel electrophoresis. PCR-EIA has a high sensitivity in detecting low DNA copy number in clinical atherosclerotic samples.

RESULTS

C. pneumoniae DNA was detected more frequently in patients with aneurysms, particular with ruptured aneurysms. The incidence of positive C. pneumoniae DNA was 73.3% in intact AAA and 10.5% in control aortas, with the highest frequency in ruptured AAA (100%) (p < 0.05).

CONCLUSION

Giving the high specificity and sensitivity of PCR-EIA, these findings support the association of C. pneumoniae in the pathogenesis of aneurysm development, growth and rupture.