Chlamydia pneumoniae in coronary and iliac arteries of Japanese patients with atherosclerotic cardiovascular diseases

The association of Chlamydia pneumoniae infection with atherosclerosis: Review and update of in vitro and animal studies

Previous studies have tended to relate Chlamydia pneumoniae (Cpn) infection to atherosclerosis. However, while serological studies have mostly reinforced this hypothesis, inconsistent and even contradictory findings have been reported in various researches. Recent papers have pointed to the significance of Cpn in atherosclerotic lesions, which are regarded as the initiator and cause of chronic inflammation. This bacterium develops atherosclerosis by phenotypic changes in vascular smooth muscle cells, dysregulation of endothelin-1 in the vascular wall, and releasing pro-inflammatory cytokines from Toll-like receptor-2 (TLR2). Furthermore, Cpn infection, particularly under hyperlipidemic conditions, enhances monocyte adhesion to endothelium; changes the physiology of the host, e.g., cholesterol homeostasis; and activates the Low-density lipoprotein (LDL) receptor, which is the initial step in atherogenesis. On the other hand, it has been reported that Cpn, even without the immune system of the host, has the ability to stimulate arterial thickening. Moreover, there is evidence that Cpn can increase the impact of the classical risk factors such as hyperlipidemia, pro-inflammatory cytokines, and smoking for atherosclerosis. Furthermore, animal studies have shown that Cpn infection can induce atherosclerotic, which alongside hyperlipidemia is a co-risk factor for cardiovascular disease. Although the exact link between Cpn and atherosclerosis has not been determined yet, previous studies have reported possible mechanisms of pathogenesis for this bacterium. Accordingly, investigating the exact role of this infection in causing atherosclerosis may be helpful in controlling the disease.

The global prevalence of Chlamydia pneumoniae, Helicobacter pylori, Cytomegalovirus and Herpes simplex virus in patients with coronary artery disease: A systematic review and meta-analysis

BACKGROUND AND AIM

Coronary Artery Disease (CAD) is one of the most important causes of death worldwide. The aim of this study was to determine the prevalence of C. pneumoniae, H. pylori, Cytomegalovirus (CMV) and Herpes simplex virus (HSV) in CAD patients based on published serological and molecular studies.

METHODS

A systematic literature search was conducted in Medline (via PubMed), Embase, Scopus and Web of Science databases (1996-2019). Both molecular and serological studies were analyzed using STATA software (Version 14).

RESULTS

145 studies were included for final analysis. We gathered and investigated the prevalence of C. pneumoniae (25.1% [95% confidence interval (CI) 21.5-28.8%]), H. pylori (12.8% [(95% CI) 4.0-22.0%]), CMV (64.4% [(95% CI) 57.7-73.0%]) and HSV (31.8% [(95% CI) 21.5-42.2%]) in CAD patients from the analysis of molecular studies. Additionally, in serological studies, the prevalence of mentioned pathogens were 72.7% [(95% CI) 67.8-77.6%], 63.3% [(95% CI) 60.0-66.5%], 62.2% [(95% CI) 58.0-66.3%] and 34.3% [(95% CI) 23.6-45.1%] respectively.

CONCLUSION

Interestingly, there was only a significant increase in the prevalence of C. pneumoniae and H. pylori in serological studies compared to the reported data from molecular studies, while the prevalence of CMV and HSV were the same in both types of studies.

Role of Chlamydia pneumoniae in atherosclerosis

Cardiovascular disease, resulting from atherosclerosis, is a leading cause of global morbidity and mortality. Genetic predisposition and classical environmental risk factors explain much of the attributable risk for cardiovascular events in populations, but other risk factors for the development and progression of atherosclerosis, which can be identified and modified, may be important therapeutic targets. Infectious agents, such as Chlamydia pneumoniae, have been proposed as contributory factors in the pathogenesis of atherosclerosis. In the present review, we consider the experimental evidence that has accumulated over the last 20 years evaluating the role of C. pneumoniae in atherosclerosis and suggest areas for future research in this field.

Lack of association between infectious burden and carotid atherosclerosis in Japanese patients

Several infectious agents, such as Chlamydia pneumoniae, cytomegalovirus (CMV), herpes simplex virus (HSV), and Helicobacter pylori, have been implicated in the pathogenesis of atherosclerosis; however, but the contribution of infection may vary among races and geographic conditions. The present study investigates the association between the presence of these pathogens and carotid atherosclerosis and examines the relevance of an infectious burden during atherogenesis in Japanese patients undergoing carotid endarterectomy. We investigated a total of 50 carotid atherosclerotic plaques resected during carotid endarterectomy by polymerase chain reaction (PCR) for C. pneumoniae, CMV, HSV, and H. pylori and by immunocytochemistry (ICC) for C. pneumoniae. We also examined the presence of antibodies to IgG and/or IgA for each pathogen in blood samples. We detected HSV DNA in 2 specimens (4%) and positive ICC for C. pneumoniae in 8 (16%). The results of PCR, ICC, or serum antibodies, as well as the number of seropositive antibodies, did not correlate with severely stenotic, ulcerative, or symptomatic plaques. Our findings indicate that the detection rate of infectious agents within atherosclerotic plaques was significantly lower in our patients than that in other studies. Thus, an inflammatory mechanism might not correlate with the pathogenesis of carotid atherosclerosis among Japanese patients with severe carotid artery stenosis.

Chlamydia pneumoniae infection enhances lectin-like oxidized low-density lipoprotein receptor (LOX-1) expression on human endothelial cells

Many studies indicate that Chlamydia pneumoniae infection is a crucial risk factor in atherogenesis. The most relevant cell type for the pathogenesis is the macrophage, which possesses classical scavenger receptors that uptake oxidized low-density lipoprotein (LDL). Here, a direct involvement of vascular endothelial cells in atherogenesis was examined employing in vitro infection of human umbilical vein endothelial cells (HUVEC) with C. pneumoniae. Chlamydia pneumoniae infection greatly enhanced the uptake of oxidized LDL, but not of acetylated LDL, by HUVEC. Among the scavenger receptors analyzed, LOX-1 transcription, which prefers oxidized LDL to acetylated LDL, was significantly amplified.

Discordant detection of Chlamydia pneumoniae in patients with carotid artery disease using polymerase chain reaction, immunofluorescence microscopy and serological methods

AIM

To determine the presence of Chlamydia pneumoniae in carotid plaque and peripheral blood mononuclear cells (PBMCs) using a combination of serology, direct antigen detection by immunofluorescence (IF) microscopy and polymerase chain reaction (PCR), and to compare the results obtained from each assay.

METHODS

A total of 54 atherosclerotic carotid plaques were tested for the presence of Chlamydia by PCR and IF methods. Of these 54 patients with carotid artery disease (CAD), 43 were also tested for the presence of C. pneumoniae DNA in PBMCs and for Chlamydia antibodies using two methods, the Medac Chlamydien rELISA and Focus Chlamydia microimmunofluorescence (MIF) methods.

RESULTS

Eighteen of the 54 (33%) carotid specimens were positive for the presence of C. pneumoniae DNA, whereas only two of 43 (5%) patients had C. pneumoniae DNA present within their PBMC fraction. Chlamydial antibodies were detected by MIF and/or rELISA in 56% (24/43) of the patients tested. None of the 43 patients was C. pneumoniae positive in all of the test specimens (plaque, PBMCs and serum).

CONCLUSIONS

Chlamydia pneumoniae is commonly found in Australian patients with CAD. Serology and PCR-based detection of C. pneumoniae in PBMCs and plaque give highly discordant results.

Is the perceived association between Chlamydia pneumoniae and vascular diseases biased by methodology?

Inter- and intralaboratory inconsistencies in detection rates of Chlamydia pneumoniae in vascular specimens have been demonstrated. In this study, 66 vascular tissue specimens from 66 patients with vascular disease were tested by three PCR assays: a 16S PCR-based reverse line blot (RLB) assay, a single-step PCR, and a nested PCR. Also, we explored the impacts of different DNA polymerase enzymes on the results based on gel electrophoresis and hybridization. The PCR results by gel electrophoresis in the single-step PCR depended on which DNA polymerase was used. All samples were negative with AmpliTaq Gold DNA polymerase, and 54.5% (36 of 66) were positive with the conventional Taq DNA polymerase. All samples were negative after hybridization with a C. pneumoniae-specific probe. In the nested PCR, all specimens were negative by gel electrophoresis and after hybridization. The RLB assay failed to detect C. pneumoniae in any specimen; however, 20 specimens were Chlamydia sp. positive. The sequence analysis of six of these samples demonstrated Chlamydia-like organisms. RLB detected Chlamydia sp. DNA in water and in the elution buffer after passage of the Qiagen columns (11 of 40). This study identified factors that may influence the detection of C. pneumoniae DNA in vascular tissues and consequently bias the perception of a link between C. pneumoniae and vascular diseases. The following are strongly recommended: to use DNA polymerases that have to be activated, to decontaminate with dUTP-uracil-DNA glycosylase, to hybridize with specific probes, to include sufficient controls, and to use molecular grade water.

Is there any relationship between Chlamydophila pneumoniae infection and juvenile idiopathic arthritis?

The role of Chlamydophila pneumoniae in the development and exacerbation of juvenile idiopathic arthritis (JIA) was investigated. Blood samples were taken from 60 JIA patients during an active disease period and for 4 weeks after. Synovial fluid samples were obtained from 20 of the 60 patients. In addition, 22 patients with familial Mediterranean fever (FMF) during the active period and 35 healthy children were included in the study as control groups. Synovial fluid samples were also obtained from three children with FMF. IgG, IgM and IgA levels against C. pneumoniae in serum samples were studied by immunofluorescence and IgG antibody and PCR studies were performed for C. pneumoniae DNA in synovial fluid samples. Twenty-nine (48.3 %) patients with JIA, 18 (81.8 %) patients with FMF and 22 (62.8 %) healthy children were found to be pre-infected with C. pneumoniae. Pre-infection with C. pneumoniae among FMF patients was found to be significantly higher than among those with JIA. We did not find a significant difference between JIA patients and healthy children. Chronic C. pneumoniae infection was observed only in six JIA patients, one FMF patient and two healthy children. Synovial fluid antibodies were found at higher than 1/512-fold dilution in one JIA patient and four times higher than normal serum in three JIA patients. C. pneumoniae DNA was not detected in any synovial fluid sample from FMF or JIA patients by PCR. In conclusion, C. pneumoniae infection does not have a triggering or a progressive effect on the clinical situation in JIA aetiopathogenesis, as a result of a multifactorial aetiology. New, extensive and serial studies (especially PCR studies of synovial tissue) are needed in order to confirm the indirect results.

Chronic infection and coronary artery disease

On a variety of fronts, chronic infection has been found to be significantly associated with the development of atherosclerosis and the clinical complications of unstable angina, myocardial infarction, and stroke. For the most part, these relationships are still just associations. Failure to confirm initial reports of serologic associations also has been common. Specific causative relationships on par with that determined between H pylori and peptic ulcer disease have not yet been established. Potential mechanisms whereby chronic infections may play a role in atherogenesis are myriad. In the case of C pneumoniae, the effect may result from direct vessel wall colonization that may damage the vessel either directly or indirectly by initiating immunologic responses. In other cases the effect may simply be that of enhancing the pre-existing chronic inflammatory response of the body to standard risk factors such as hyperlipidemia. Even though the infectious agent may not directly infect the vessel wall, it may perform its critical role from afar. Chronic infection might also influence pre-existing plaque by enhancing T-cell activation or other inflammatory responses that may participate in the destabilization of the intimal cap. Hence chronic infection may play a role either in the initiation, progression, or the destabilization of atherosclerotic plaques. The infectious agents with the most evidence to support an etiologic role in atherosclerosis include C pneumoniae and cytomegalovirus. Evidence is mounting for a variety of other potential agents including other herpes viruses, influenza, other specific bacteria (such as M pneumoniae), and chronic infections with common bacterial agents (periodontal disease, chronic bronchitis, and chronic urinary tract infection, among others) [191]. Future studies are expected to elucidate further the pathophysiologic relationship between chronic infection and atherosclerosis and to evaluate further the potential of a variety of treatment approaches, including antibiotics.

Evaluation of five DNA extraction methods for purification of DNA from atherosclerotic tissue and estimation of prevalence of Chlamydia pneumoniae in tissue from a Danish population undergoing vascular repair

BACKGROUND

To date PCR detection of Chlamydia pneumoniae DNA in atherosclerotic lesions from Danish patients has been unsuccessful. To establish whether non-detection was caused by a suboptimal DNA extraction method, we tested five different DNA extraction methods for purification of DNA from atherosclerotic tissue.

RESULTS

The five different DNA extraction methods were tested on homogenate of atherosclerotic tissue spiked with C. pneumoniae DNA or EB, on pure C. pneumoniae DNA samples and on whole C. pneumoniae EB. Recovery of DNA was measured with a C. pneumoniae-specific quantitative real-time PCR. A DNA extraction method based on DNA-binding to spin columns with a silica-gel membrane (DNeasy Tissue kit) showed the highest recovery rate for the tissue samples and pure DNA samples. However, an automated extraction method based on magnetic glass particles (MagNA Pure) performed best on intact EB and atherosclerotic tissue spiked with EB. The DNeasy Tissue kit and MagNA Pure methods and the highly sensitive real-time PCR were subsequently used on 78 atherosclerotic tissue samples from Danish patients undergoing vascular repair. None of the samples were positive for C. pneumoniae DNA. The atherosclerotic samples were tested for inhibition by spiking with two different, known amounts of C. pneumoniae DNA and no samples showed inhibition.

CONCLUSION

As a highly sensitive PCR method and an optimised DNA extraction method were used, non-detection in atherosclerotic tissue from the Danish population was probably not caused by use of inappropriate methods. However, more samples may need to be analysed per patient to be completely certain on this. Possible methodological and epidemiological reasons for non-detection of C. pneumoniae DNA in atherosclerotic tissue from the Danish population are discussed. Further testing of DNA extraction methods is needed as this study has shown considerable intra- and inter-method variation in DNA recovery.

Aspirin inhibits Chlamydia pneumoniae-induced NF-kappa B activation, cyclo-oxygenase-2 expression and prostaglandin E2 synthesis and attenuates chlamydial growth

Infection with Chlamydia pneumoniae has been implicated as a potential risk factor for atherosclerosis. This study was designed to investigate the mechanisms of the anti-chlamydial activity of aspirin. A reporter gene assay for NF-kappa B activity, immunoblot analysis for cyclo-oxygenase (COX)-2 and radioimmunoassay for prostaglandin E(2) (PGE(2)) were performed. Following infection of HEp-2 cells with C. pneumoniae, NF-kappa B was activated, COX-2 was induced and PGE(2) was elevated. Aspirin inhibited NF-kappa B activation at a concentration of 0.1 mM, partially inhibited COX-2 induction and blocked PGE(2) synthesis completely. In addition, high doses of aspirin (1 and 2 mM) inhibited chlamydial growth in HEp-2 cells, decreasing the number and size of inclusion bodies; this effect could be overcome by adding tryptophan to the culture. Indomethacin also blocked the synthesis of PGE(2), but had no effect on COX-2 expression or chlamydial growth. These results indicate that aspirin not only has an anti-inflammatory activity through prevention of NF-kappa B activation but also has anti-chlamydial activity at high doses, possibly through depletion of tryptophan in HEp-2 cells.

Chlamydia pneumoniae and coronary artery disease: the antibiotic trials

Parallel with the mounting evidence that atherosclerosis has a major inflammatory component, provoking agents that may initiate and drive this process have been sought. Infectious agents such as Chlamydia pneumoniae have been alleged to be activators of inflammation that may contribute to atherosclerosis and thus coronary artery disease (CAD) and its associated complications. A logical pneumoniae extension of this theory whether treating C pneumoniae infection with antibiotics and/or modulating inflammatory processes can affect CAD and its sequelae. This article discusses the potential role of C pneumoniae in atherosclerosis, its detection, and the rationale for antibiotics. Additionally, it summarizes the current randomized clinical trials of antichlamydial antibiotics in patients with CAD and draws conclusions based on the results.

Chlamydia pneumoniae in atherosclerotic lesions of patients undergoing vascular surgery

The pathophysiological implications of Chlamydia pneumoniae in atherosclerotic lesions and its contribution to atherosclerotic complications remain unclear. Therefore, the purpose of the present study was to evaluate whether or not there is an association between the presence of Chlamydia pneumoniae in atherosclerotic lesions and the clinical manifestations as well as risk factors of atherosclerotic disease in patients undergoing vascular surgery. Specimens from atherosclerotic arteries were collected during endarterectomy of the carotid artery (n = 15), endarterectomy of the femoral artery (n = 19), or repair of an abdominal aortic aneurysm (n = 28). Detection of Chlamydia pneumoniae was performed by using immunohistochemical staining (IHC) with specific antibodies. Clinical manifestations of atherosclerotic disease were defined by the presence of cardiovascular risk factors, coronary heart disease, and previous vascular surgery. Inflammatory serum markers were determined in all patients prior to surgery. The specimens of all 62 patients revealed severe atherosclerosis in histological examination and a positive IHC was observed in 41 samples (66%). There were no differences regarding cardiovascular risk factors, coronary heart disease, events of previous vascular surgery, or inflammatory serum markers when comparing patients with positive and negative IHC. In conclusion, our findings showed no correlation between clinical or laboratory parameters of atherosclerosis and the presence of Chlamydia pneumoniae in atherosclerotic lesions. Therefore, Chlamydia pneumoniae appears to be a concomitant phenomenon rather than a causative principle in atherosclerosis.

Chlamydia pneumoniae and atherosclerosis: critical assessment of diagnostic methods and relevance to treatment studies

A number of studies have found that inflammation of the vessel wall plays an essential role in both the initiation and progression of atherosclerosis and erosion and fissure and the eventual rupture of plaques. Chlamydia pneumoniae is one of the infectious agents that have been investigated as possible causes of this inflammation. Initial studies of the association of C. pneumoniae and cardiovascular disease (CVD) were seroepidemiologic, and these were followed by studies in which the organism was identified in vascular tissue from patients with CVD by electron microscopy, PCR and immunocytochemical staining (ICC). C. pneumoniae has also been isolated by culture from vascular tissue in a small number patients. However, no single serologic, PCR, or ICC assay has been used consistently across all studies. The assays used are also not standardized. Recent studies of serologic and PCR assays for diagnosis of C. pneumoniae infection have suggested that there may be substantial interlaboratory variation in the performance of these tests. It now appears that some of the inconsistency of results from study to study may be due, in part, to lack of standardized methods. Although initial seroepidemiologic studies demonstrated a significantly increased risk of adverse cardiac outcome in patients who were seropositive, subsequent prospective studies found either small or no increased risk. In addition to the lack of consistent serologic criteria, recent evaluations have demonstrated inherent problems with performance of the most widely used serologic methods. Most importantly, we do not have a reliable serologic marker for chronic or persistent C. pneumoniae infection.

Secondary prevention of coronary artery disease with antimicrobials: current status and future directions

Over the past several decades, coronary artery disease (CAD) has become the major health problem in the Western world with more than 50% of deaths attributed to its complications. The exact causes of atherosclerosis are not clearly known, although multiple risk factors (e.g. hypertension, hyperlipidemia, diabetes mellitus, family history, and smoking) have been well described. However, these risk factors account for only about 50% of the total risk of CAD. Consequently, an ongoing search is under way to discover new risk factors for atherosclerosis as well as the basic underlying causes of progression. Although the evidence is not yet definitive, recent studies have shown that chronic infection by such bacterial organisms as Chlamydia pneumoniae, Helicobacter pylori, and a variety of dental pathogens may play a causative role in atherosclerosis. If this is true, then antimicrobial therapy may be helpful in the secondary prevention of CAD. Indeed, several small studies have already been completed testing this hypothesis. This article reviews the evidence associating these bacterial pathogens to CAD and presently available information regarding the use of antibiotics in the setting. At present, most studies evaluating the potential efficacy antimicrobials in the secondary prevention of CAD have tested the use of macrolide antibodies. Although several small preliminary studies have reported promising results favoring a clinical benefit from even short (<3 months) courses of antimicrobial therapy, the first large clinical trial, the Weekly Intervention with Zithromax for Atherosclerosis and its Related Disorders (WIZARD) study, did not show a statistically significant beneficial effect of a 3 month course of azithromycin over placebo by the end of up to 4 years follow-up. However, a statistically significant (p = 0.03) 33% reduction in death and myocardial infarction was found at 6 months, 3 months after the discontinuation of antibiotics. This robust clinical benefit, however, was not sustained over the ensuing 3.5 years of follow-up. These disappointing long-term outcomes of short-term therapy with antimicrobials may be explained by the recently discovered difficulty found in eradicating chronic vascular infections such as C. pneumoniae. It remains possible that longer term antimicrobial therapy or short-term use of more potent single agents or combinations, capable of effectively eradicating the offending organisms might provide added clinical benefit in the fight against CAD. Further studies are ongoing or planned to evaluate this potential. In the meantime, it is not presently recommended that antimicrobials be routinely prescribed for the secondary prevention of CAD.

Analysis of the serological response to Chlamydia pneumoniae in patients with ischemic heart disease by recombinant MOMP-ELISA

To investigate the humoral immune response to the major outer membrane protein (MOMP) of Chlamydia pneumoniae, a fusion protein, thioredoxin-(His)6-MOMP (rMOMP) was produced in Escherichia coli and purified; this served as an antigen to establish an enzyme-linked immunosorbent assay (ELISA). Specific IgG and IgA antibodies against rMOMP were determined in sera from patients with ischemic heart disease. The findings were compared with those obtained by ELISA using the outer membrane protein complex (Hitazyme). The positivity rates for IgG antibody by rMOMP-ELISA were low (28%) compared with those by Hitazyme (72%). However, the positivity rates of IgA antibody by rMOMP-ELISA were similar to those by Hitazyme (76%). Interestingly, antigen positivity by immunohistochemical staining in the atherosclerotic lesions of coronary arteries was high in the groups with a high IgA titer of rMOMP-ELISA.

Standardizing Chlamydia pneumoniae assays: recommendations from the Centers for Disease Control and Prevention (USA) and the Laboratory Centre for Disease Control (Canada)

Chlamydia pneumoniae has been associated with atherosclerosis and several other chronic diseases, but reports from different laboratories are highly variable and "gold standards" are lacking, which has led to calls for more standardized approaches to diagnostic testing. Using leading researchers in the field, we reviewed the available approaches to serological testing, culture, DNA amplification, and tissue diagnostics to make specific recommendations. With regard to serological testing, only use of microimmunofluorescence is recommended, standardized definitions for "acute infection" and "past exposure" are proposed, and the use of single immunoglobulin (Ig) G titers for determining acute infection and IgA for determining chronic infection are discouraged. Confirmation of a positive culture result requires propagation of the isolate or confirmation by use of polymerase chain reaction (PCR). Four of 18 PCR assays described in published reports met the proposed validation criteria. More consistent use of control antibodies and tissues and improvement in skill at identifying staining artifacts are necessary to avoid false-positive results of immunohistochemical staining. These standards should be applied in future investigations and periodically modified as indicated.

The association of infection and coronary artery disease: an update

Numerous studies have reported an association of coronary atherosclerosis and restenosis with certain bacterial and viral infections. This article reviews the pathophysiology of atherosclerosis, the role of infectious agents (cytomegalovirus, Chlamydia pneumoniae and Helicobacter pylori) in atherogenesis and studies supporting the potential beneficial effects of antibiotics or antiviral agents in the management of atherosclerotic disease. The interactions of cytomegalovirus and the arterial wall have been extensively studied. However, despite the successful preliminary therapeutic trials with the use of macrolides in augmenting possible C. pneumoniae-induced cardiovascular events, the exact mechanisms of how C. pneumoniae enters the arterial wall remains unknown at this point. For H. pylori, regardless of the large number of studies performed to assess the association between H. pylori and coronary artery disease, no definitive conclusion could be made at this time, due to contradictory results. Before one can widely adopt the use of antibiotics or antiviral agents as treatment for atherosclerosis, further studies must be designed to address some important issues. In vivo animal models need to be established to further examine the various hypotheses regarding the interaction of infectious agents and atherosclerosis and restenosis. Large-scale prospective cohort studies should be designed to relate evidence of infection to future risk of cardiovascular diseases. Confounding variables, such as other cardiovascular risk factors and socio-economic status, should be controlled in order to strengthen the association. Further interventional studies are also required to establish the best antibiotic or antiviral regimen to maximise efficacy and minimise side effects.

Infections and atherosclerosis

More than a century ago, inflammation and infection were considered to have atherogenic effects. During last century, however, this hypothesis was completely abandoned, and the old idea that coronary heart disease (CHD) possibly has an infectious etiology has only re-emerged in recent years. Both viral and bacterial pathogens have been proposed to be associated with the inflammatory changes found in atherosclerosis. Herpes group viruses, especially cytomegalovirus (CMV) and herpes simplex virus type 1 (HSV1), have been associated with both atherosclerosis and restenosis. Helicobacter pylori and dental infections have also been linked to CHD, but the evidence is strongest for a respiratory tract bacterium, Chlamydia pneumoniae. The association was originally found in seroepidemiological studies, but the presence of organisms in atherosclerotic lesions, the first animal studies and preliminary successful intervention trials with antibiotics suggest that C. pneumoniae may have a pathogenetic role in the disease. The causal relationship has not yet been proven, but ongoing large intervention trials and research on pathogenetic mechanisms may lead to the use of antimicrobial agents in the treatment of CHD in the future.

Chlamydia pneumoniae in atherosclerotic and nonatherosclerotic tissue

The positivity rate and localization of Chlamydia pneumoniae were investigated in atherosclerotic and nonatherosclerotic tissues by immunohistochemistry, polymerase chain reaction, and cell culture. In total, 67 atheromatous plaques from Japanese symptomatic patients and 110 nonatherosclerotic tissues and organs were evaluated. Of these, 62% of atherosclerotic plaques from symptomatic patients were infected with C. pneumoniae compared with just 2% of nonatherosclerotic tissues. Immunohistochemically stained C. pneumoniae were found most often in smooth muscle cells, less often in macrophages, and in a few endothelial cells.

Detection of Chlamydia pneumoniae in arterial tissues

In literature in which detection of Chlamydia pneumoniae in the artery is described, the methods used were immunocytochemistry (ICC), polymerase chain reaction (PCR), electron microscopy, and isolation. These studies demonstrated the presence of the organism in atheromatous lesions. The organism was detected frequently by ICC and PCR in atheromatous tissues (approximately 50% of subjects) but rarely in normal arteries (approximately 1% of subjects). There has been poor correlation between detection and serology. Detection studies have been used to assess the etiologic role of C. pneumoniae in atherosclerosis and to determine whether C. pneumoniae infection contributes to acute cardiovascular events. Although these studies produced suggestive evidence of an etiologic role, the use of observational studies to obtain a definitive answer is difficult. Therefore, investigators are increasingly concentrating their efforts on studies that use animal models, in vitro cultured arterial cells, and therapeutic trials in humans to determine the pathogenic role of the organism in atherosclerosis.

Inflammation, infection and atherosclerosis: do antibacterials have a role in the therapy of coronary artery disease?

Since the recent publication of 3 studies on the use of antibacterials in patients with coronary artery disease (CAD), there has been a phenomenal interest in the role of infection in the genesis of CAD. It is now generally accepted that inflammation accompanies atherosclerosis from its initiation to the evolution of end-events. Inflammation may occur in response to traditional risk factors, such as hyperlipidaemia, smoking and diabetes mellitus. There is a recent resurgence of the concept that inflammation may have an infectious basis. This concept is based on the identification of microorganisms in the atherosclerotic plaque and seropositivity. The data on eradication of the offending organism with antibiotics and prevention of atherosclerosis-related events have, however, been inconsistent. This may reflect lack of precise understanding of steps leading to atherosclerosis and the evolution of acute ischaemic events. Further work in this area may help identify subsets of patient populations within which infection may play a causative role in the genesis of CAD. Targeted therapy then may be considered logical.

Chronic infection and coronary artery disease

On a variety of fronts, chronic infection has been found to be significantly associated with the development of atherosclerosis and the clinical complications of unstable angina, myocardial infarction, and stroke. For the most part, these are still just associations. Specific causative relationships on par with that determined between H. pylori and peptic ulcer disease have not yet been established. Potential mechanisms whereby chronic infections may play a role in atherogenesis are myriad. In the case of C. pneumoniae, the effect may result from direct vessel wall colonization, which may damage the vessel directly or indirectly by initiating immunologic responses. In other cases, the effect may simply be that of enhancing the preexisting chronic inflammatory response of the body to standard risk factors, such as hyperlipidemia. Even though the infectious agent may not directly infect the vessel wall, it may perform its critical role from afar. Chronic infection might also influence preexisting plaque by enhancing T cell activation or other inflammatory responses that may participate in the destabilization of the intimal cap. Chronic infection may play a role in the initiation, progression, or destabilization of atherosclerotic plaques. The infectious agents with the most evidence to support a causative role in atherosclerosis include C. pneumoniae and cytomegalovirus. Evidence is mounting for a variety of other potential agents, including H. pylori, various periodontal agents, and even hepatitis A. Future studies are expected to elucidate further the pathophysiologic relationship between chronic infection and atherosclerosis and to evaluate the potential of a variety of treatment approaches, including antibiotics.

From plaque biology to clinical setting

Coronary atherosclerosis may cause acute and chronic ischemic syndromes; the former are caused by "acute plaque events," mostly thrombosis complicating vulnerable ruptured plaques, namely severe lesions with large core, thin cap, and weak shoulder infiltrated by activated inflammatory cells. Plaque rupture may also occur in nonischemic settings and is not obligatorily complicated by thrombosis. Furthermore, plaque rupture is not the only thrombus substrate in acute ischemic syndromes: Superficial erosion of fibrous plaques is found in 44% of acute thrombi in sudden coronary deaths and in 25% of those in acute myocardial infarctions. Coronary thrombosis appears to be triggered by superficial intimal inflammation in plaque ulceration and by neointimal hyperplasia in plaque erosion. "Endogenous" and, recently, exogenous factors, particularly infective intracellular organisms, have been proposed as major contributors to plaque inflammation, activation, and vulnerability. Possible exogenous triggers are DNA and RNA viruses and intracellular bacteria such as Chlamydia pneumoniae, which has been identified with microbiological, ultrastructural, immunohistochemical, and molecular tools in a consistent proportion of human plaque samples. Chlamydia increases local thrombogenicity and is associated with an atherogenic lipid profile. Systemic indexes of inflammation, such as PCR, SAA, and fibrinogen, are also increased in acute syndromes and common infectious diseases with high morbidity and minimal clinical impact are good candidates; Helicobacter pylori is a major one. Infectious agents could link local and systemic inflammation: White cells infected in its target tissue could circulate into the flow and be captured, on a specific local trigger, into vessel walls thus stimulating local inflammation.