Co-infection with Chlamydia pneumoniae and Helicobacter pylori results in vascular endothelial dysfunction and enhanced VCAM-1 expression in apoE-knockout mice

Helicobacter pylori Infection Maybe a Risk Factor for Cardiac Syndrome X

Purpose

Cardiac syndrome X (CSX) is a condition with normal coronary angiography but angina pectoris. Chronic inflammation caused by Helicobacter pylori (H. pylori) infection may play a pathogenic role in CSX. Therefore, we conducted a meta-analysis to explore the relationship between H. pylori infection and risk of CSX.

Methods

A systematic search in the Web of Science, Medline, Embase and Chinese databases (CNKI and Wanfang) was conducted up to October 2021. Articles on the association between H. pylori infection and the risk of CSX were included and were analyzed by R software (version 4.1.0).

Results

Ten case-control studies involving 703 CSX patients and 731 healthy controls were included. H. pylori infection was associated with an increased risk of CSX (OR: 8.29, 95% CI: 4.64–14.82). We also found a significant association in those 25–40 years of age (OR: 1.34, 95% CI: 1.04–1.72), those 40–50 years of age (OR: 11.27, 95% CI: 4.29–29.61), those over 50 years of age (OR: 7.18, 95% CI: 3.59–14.36), those in developing countries [Iran (OR: 12.99, 95% CI: 8.61–19.60) and China (OR: 5.14, 95% CI: 3.09–8.56)]. However, this association was not apparent in a developed country [Italy (OR: 0.93, 95% CI: 0.37–2.33)].

Conclusions

Our study suggested a possible association between H. pylori infection and the risk of CSX. Its pathogenicity is stronger in middle-aged individuals and some developing countries. However, more studies are needed to further investigate whether early eradication of H. pylori can reduce the incidence rate of CSX, especially in middle-aged individuals and some developing countries.

Helicobacter pylori infection and the progression of atherosclerosis: A systematic review and meta-analysis

OBJECTIVE

In recent years, many studies have tried to prove whether Helicobacter pylori (H. pylori) can promote the progression of atherosclerosis (AS), but the reported results are conflicting. Carotid intima-media thickness (CIMT), flow-mediated dilation (FMD), or pulse wave velocity (PWV) are the most commonly used indicators to evaluate the progress of AS. So, we collected and evaluated these three indicators to provide evidence-based medicine for the clinic.

MATERIALS AND METHODS

We included and evaluated studies on H. pylori infection and CIMT, FMD, or PWV from PubMed, Cochrane trials, and Embase databases before September 1, 2021, and language restrictions: English. Research types include cross-sectional studies, cohort studies, and case-control studies. The MINORS scale was used to evaluate the quality of these studies. For all studies, we choose a random-effects model and calculate the weighted mean difference (WMD) for analysis, and all our analyses use STATA software.

RESULTS

Meta-analysis shows that H. pylori infection can significantly increase CIMT (WMD = 0.059, 95% CI: 0.039, 0.079, p < 0.001). Based on subgroup analysis, we found that the relationship between the two is more significant in the young and middle-aged people younger than 60 years old and people without cardiovascular disease. In addition, we also found an association between H. pylori infection and FMD (WMD = -3.873, 95% CI: -5.684, -2.062, p < 0.001), but it is a pity that there are few literatures that meet the standards. Finally, We concluded that H. pylori infection can significantly increase PWV (WMD = 88.033, 95%CI: 67.297,108.768. I²  = 99.63%, p < 0.001). In the subgroup analysis, we also found that this correlation is similar to CIMT, and it is more significant in the young and middle-aged population under 60 and those without cardiovascular disease. We also found in the sub-analysis that there was a significant increase in CIMT in CagA-positive individuals in H. pylori-infected patients (WMD = 0.16, 95%CI: 0.02, 0.29. p = 0.03).

CONCLUSION

Helicobacter pylori infection can promote the process of AS, especially in people under the age of 60 and people without cardiovascular risk factors, and we hope that our meta-analysis can provide ideas for the early prevention of AS.

Association between Helicobacter Pylori Infection and Systemic Arterial Hypertension: A Meta-Analysis

Fundamento:

Estudos epidemiológicos recentes demonstraram que alterações na microbiota e seus metabólitos estão associadas à hipertensão arterial sistêmica. A Helicobacter pylori (H. pylori) é um dos patógenos bacterianos mais comuns, e a possível associação entre a infecção por H. pylori e a hipertensão é controversa.

Objetivos:

Este estudo teve o objetivo de esclarecer a associação entre eles e proporcionar uma nova base teórica para detectar a patogênese da hipertensão.

Métodos:

Foram selecionados estudos caso-controle e transversais sobre a associação entre H. pylori e hipertensão, publicados de 1996 a 2019 indexados nos bancos de dados PubMed, Google Scholar, Chinese Wan Fang Data, e Chinese National Knowledge Infrastructure (CNKI). As razões de chance (RC) combinadas e o intervalo de confiança (IC) 95% foram estimados. O I² foi realizado para avaliar a heterogeneidade estatística. O viés de publicação foi avaliado utilizando-se os testes de Beggs e de Egger. Os dados extraídos foram analisados no software Stata 12.0. A significância estatística foi definida com um p-valor < 0,05.

Resultados:

Foram cadastrados 17 estudos envolvendo 6376 casos de hipertensão e 10850 controles. A taxa de infecção por H. pylori em pacientes hipertensos e em controles foi de 64,9% e 56,3%, respectivamente. Foi demonstrada uma associação significativamente positiva entre a infecção por H. pylori e a hipertensão, com uma RC global de 2,07 (IC 95%: 1,46–2,94; p < 0,05). A análise de subgrupos revelou que a prevalência de infecção por H. pylori foi associada à hipertensão na região da Ásia e no grupo de caso-controle, as RC (IC 95%) foram 2,26 (1,51-3,38) e 2,53 (1,72-3,72), respectivamente. Depois de estratificar por métodos de detecção, ainda existiam diferenças entre os subgrupos (todos p < 0,05).

Conclusão:

Esta metanálise indicou que a infecção por H. pylori está associada positivamente à hipertensão.

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.

Microbial modulation of cardiovascular disease

Although diet has long been known to contribute to the pathogenesis of cardiovascular disease (CVD), research over the past decade has revealed an unexpected interplay between nutrient intake, gut microbial metabolism and the host to modify the risk of developing CVD. Microbial-associated molecular patterns are sensed by host pattern recognition receptors and have been suggested to drive CVD pathogenesis. In addition, the host microbiota produces various metabolites, such as trimethylamine-N-oxide, short-chain fatty acids and secondary bile acids, that affect CVD pathogenesis. These recent advances support the notion that targeting the interactions between the host and microorganisms may hold promise for the prevention or treatment of CVD. In this Review, we summarize our current knowledge of the gut microbial mechanisms that drive CVD, with special emphasis on therapeutic interventions, and we highlight the need to establish causal links between microbial pathways and CVD pathogenesis.

Serum and Mucosal Cytokine Profiles in Patients with Active Helicobacter Pylori and Ischemic Heart Disease: Is There a Relationship?

This study is designed to investigate, for the first time, circulating and gastric mucosal levels of IL1-α, IL-6, IL-8 and TNF-α in patients with ischemic heart disease (IHD) and matched controls, according to the presence or absence of active Helicobacter pylori infection. Furthermore, in order to evaluate whether modified lipid profile was associated to an increased cardiovascular risk, this was determined in the same groups. Cytokine levels were measured using ELISA in 58 patients with IHD and 52 controls. Active H. pylori infection was assessed if either culture of H. pylori or rapid urease test gave a positive result. Our findings indicate increasing cytokine mucosal levels in H. pylori-positive patients compared to H. pylori-negative subjects. However, the increase was statistically significant only for IL-6 and TNF-α in the gastric mucosa of IHD patients. In H. pylori-positive controls, IL-8 mucosal levels positively correlated with both IL-1α (r = 0.98; P = 0.0003) and IL-6 (r = 0.83; P = 0.03) levels. Circulating cytokine levels were comparable in IHD and healthy subjects, regardless of H. pylori status. There were no correlations between mucosal and circulating cytokine levels. Active H. pylori infection was not associated with a modified lipid profile in either controls or IHD patients, although ApoAI levels were significantly higher in H. fly/ort'-positive controls compared to those H. pylori-negative. Taken together, the results of the present study provide evidence that active H. pylori infection may play a role as a trigger factor in the pathophysiology of IHD by inducing an inflammatory cascade concentrated on gastric mucosa.

Putative consequences of exposure to Helicobacter pylori infection in patients with coronary heart disease in terms of humoral immune response and inflammation

INTRODUCTION

Pathogens, including Helicobacter pylori (Hp), have been suggested to contribute to the development of coronary heart disease (CHD), although the evidence still remains insufficient. The study was focused on the exposure of CHD patients to Hp and resulting anti-Hp heat shock protein B HspB antibody production in relation to the level of serum lipopolysaccharide binding protein (LBP) as a marker of inflammation.

MATERIAL AND METHODS

One hundred seventy CHD patients and 58 non-CHD individuals participated in this study. Coronary angiography confirmed the atheromatic background of CHD. The panel of classical risk factors included: arterial hypertension, diabetes, total cholesterol, low-density lipoprotein (LDL)/high-density lipoprotein (HDL) cholesterol, triglycerides, obesity and nicotinism. The Hp status was estimated by (13)C urea breath test and serology. Immunoblot and ELISA were used for screening the sera samples for anti-Hp HspB immunoglobulins (Igs) and LBP.

RESULTS

Coronary heart disease patients were exposed to Hp more frequently than non-CHD individuals. This was associated with increased levels of specific anti-Hp IgG2 and IgA as well as total IgA. Hp infected CHD and non-CHD donors produced anti-Hp HspB IgG cross-reacting with human Hsp 60. In CHD patients the LBP level was significantly higher in comparison to non-CHD donors. This was related to the severity of the disease. Type I Hp strains stimulated higher LBP levels than less pathogenic type II isolates.

CONCLUSIONS

Lipopolysaccharide binding protein secreted in excess together with anti-Hp HspB, cross-reacting with human Hsp60, may increase the risk of vascular pathologies in Hp-exposed CHD patients.

Infection and Atherosclerosis Development

Atherosclerosis is a chronic disease hallmarked by chronic inflammation, endothelial dysfunction and lipid accumulation in the vasculature. Although lipid modification and deposition are thought to be a major source of the continuous inflammatory stimulus, a large body of evidence suggests that infectious agents may contribute to atherosclerotic processes. This could occur by either direct effects through infection of vascular cells and/or through indirect effects by induction of cytokine and acute phase reactant proteins by infection at other sites. Multiple bacterial and viral pathogens have been associated with atherosclerosis by seroepidemiological studies, identification of the infectious agent in human atherosclerotic tissue, and experimental studies demonstrating an acceleration of atherosclerosis following infection in animal models of atherosclerosis. This review will focus on those infectious agents for which biological plausibility has been demonstrated in animal models and on the challenges of proving a role of infection in human atherosclerotic disease.

Infectious burden and atherosclerosis: A clinical issue

Atherosclerotic cardiovascular diseases, chronic inflammatory diseases of multifactorial etiology, are the leading cause of death worldwide. In the last decade, more infectious agents, labeled as “infectious burden”, rather than any single pathogen, have been showed to contribute to the development of atherosclerosis through different mechanisms. Some microorganisms, such as Chlamydia pneumoniae (C. pneumoniae), human cytomegalovirus, etc. may act directly on the arterial wall contributing to endothelial dysfunction, foam cell formation, smooth muscle cell proliferation, platelet aggregation as well as cytokine, reactive oxygen specie, growth factor, and cellular adhesion molecule production. Others, such as Helicobacter pylori (H. pylori), influenza virus, etc. may induce a systemic inflammation which in turn may damage the vascular wall (e.g., by cytokines and proteases). Moreover, another indirect mechanism by which some infectious agents (such as H. pylori, C. pneumoniae, periodontal pathogens, etc.) may play a role in the pathogenesis of atherosclerosis is molecular mimicry. Given the complexity of the mechanisms by which each microorganism may contribute to atherosclerosis, defining the interplay of more infectious agents is far more difficult because the pro-atherogenic effect of each pathogen might be amplified. Clearly, continued research and a greater awareness will be helpful to improve our knowledge on the complex interaction between the infectious burden and atherosclerosis.

Resveratrol supplementation reduces aortic atherosclerosis and calcification and attenuates loss of aerobic capacity in a mouse model of uremia

The polyphenolic compound resveratrol (RSV) has been studied for its protective effects on a variety of conditions, including cardiovascular disease (CVD), reduced exercise capacity, and bone disease. Individuals with chronic kidney disease suffer from a variety of these comorbid conditions, but the efficacy of RSV supplementation in this population is unknown. The objective of this study was to determine the efficacy of resveratrol feeding on factors related to CVD, aerobic capacity, and bone health in a mouse model of uremia. At 8 weeks of age, 28 female apolipoprotein E⁻/⁻ mice underwent a two-step surgical procedure to induce uremia and were randomized to one of the two treatment groups for 16 weeks: 0.04% w/w resveratrol supplemented diet (group designated as RSV) (n=12) or control diet (group designated as CON) (n=16). Cardiovascular risk was determined by analysis of aortic atherosclerotic lesion area and aortic calcium, aerobic capacity was measured by maximal oxygen consumption/maximal aerobic capacity (VO(₂max)) testing, and bone microarchitecture was assessed by microcomputed tomography. RSV animals had significantly fewer aortic atherosclerotic lesions at the site of the ascending aorta and lower aortic calcium at the branch of the coronary arteries compared with CON. Furthermore, there was a significant decline in VO(₂max) from baseline to final testing in the CON group, but VO(₂max) was preserved in the RSV group. Last, RSV had no significant effect on bone architecture. These data indicate that RSV supplementation improves vascular health and preserves aerobic capacity in a model of uremia, suggesting RSV supplementation could be examined as a therapeutic strategy for a critically ill population.

Association of pathogen burden and hypertension: the Persian Gulf Healthy Heart Study

BACKGROUND

Chronic infection with cytomegalovirus (CMV), Chlamydia pneumoniae, herpes simplex virus 1 (HSV-1), and Helicobacter pylori may contribute to essential hypertension. However, the evidence now available does not clarify whether the aggregate number of pathogens (pathogen burden) may be associated with hypertension.

METHODS

Sera from 1,754 men and women aged ≥25 years were analyzed for immunoglobulin G antibodies to C. pneumoniae, HSV-1, H. pylori, and CMV using enzyme-linked immunosorbent assay. The aggregate number of seropositives to the studied viral and bacterial agents was defined as pathogen burden. Hypertension was defined according to World Health Organization criteria.

RESULTS

A total of 459 (26.3%) of the subjects had hypertension. In the hypertensive group, 4.2% had 0 or 1 pathogens present, 20.6% had 2, 43.2% had 3, and 32.1% had 4; in the normotensive group, 7.9% had 0 or 1, 28.4% had 2, 42.7% had 3, and 21.0% had 4. Of the 4 studied pathogens, H. pylori seropositivity showed a significant independent association with hypertension (odds ratio (OR) =1.37; 95% confidence interval (CI) =1.05-1.79; P = 0.02). In multiple logistic regression analyses, the pathogen burden did not show a significant independent association with hypertension. Coinfection with H. pylori and C. pneumoniae was significantly associated with hypertension compared with double seronegativity after adjustment for age, sex, chronic low-grade inflammation, and cardiovascular risk factors (OR = 1.68; 95% CI = 1.14-2.47; P = 0.008].

CONCLUSIONS

The pathogen burden was not associated with hypertension. However, coinfection with C. pneumoniae and H. pylori showed a significant association with essential hypertension, independent of cardiovascular risk factors and chronic low-grade inflammation.

Soy protein diet and exercise training increase relative bone volume and enhance bone microarchitecture in a mouse model of uremia

Soy protein consumption and exercise training have been widely studied for their effects on the vasculature and bone in healthy populations, but little is known about the effectiveness of these interventions in chronic kidney disease (CKD). Cardiovascular disease and bone fracture risk are significantly elevated in CKD, and current pharmacological interventions have been unsuccessful in treating these conditions simultaneously. The purpose of this study was to compare the effects of a soy protein diet and endurance exercise training, alone or in combination, on cardiovascular and bone health in a mouse model of renal insufficiency. At 8 weeks of age, 60 female apolipoprotein E(-/-) mice underwent a two-step surgical procedure to induce uremia. These mice were then randomized at 12 weeks of age to one of four treatment groups for the 16-week intervention period: sedentary, control diet (n = 16); sedentary, soy protein diet (n = 18); exercise, control diet (n = 14); and exercise, soy protein diet (n = 12). There were no significant treatment effects on atherosclerotic lesion areas or aortic calcium deposits. We demonstrated a significant main effect of both diet and exercise on relative bone volume, trabecular number, trabecular separation, and trabecular connective density in the proximal femur as measured by microcomputed tomography. There were no treatment effects on trabecular thickness. We also showed a main effect of diet on plasma urea levels. These data suggest that soy protein intake and exercise training exert beneficial effects on properties of bone and plasma urea levels in mice with surgically induced renal impairment.

The effect of proatherogenic microbes on macrophage cholesterol homeostasis in apoE-deficient mice

BACKGROUND

Pathogens such as Aggregatibacter actinomycetemcomitans (Aa) and Chlamydia pneumoniae (Cpn) associate with an increased risk for cardiovascular diseases by inducing inflammation. We hypothesized that the pathogens affect the vascular wall by disturbing cholesterol homeostasis and endothelial function.

METHODS

Aa- and Cpn-infections were induced in apoE-deficient mice by intravenous and intranasal applications, respectively. Cholesterol efflux from mouse peritoneal macrophages to apo(lipoprotein)A-I was assessed. The efflux capacity of mouse sera as acceptors of cholesterol from RAW264.7-macrophages was determined. Additionally, endothelial function was studied by following the relaxation capacity of rat mesenteric arteries after incubation in the conditioned culture media of the peritoneal macrophages isolated from the mice.

RESULTS

Infection increased serum phospholipid transfer protein (PLTP) and lipopolysaccharide (LPS) activity, as well as serum amyloid A (SAA) and TNF-α concentrations. Peritoneal macrophages of mice with Aa-infection showed increased cholesterol uptake and reduced cholesterol efflux. Sera of Cpn and Cpn + Aa-infected mice had reduced cholesterol efflux capacity from RAW264.7-macrophages. Conditioned macrophage medium from mice with chronic C. pneumoniae infection induced endothelial dysfunction. Additionally, concentrations of serum adhesion molecules, intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM) in Cpn-groups and E-selectin in Cpn + Aa-group, were elevated. The serum markers of endothelial function correlated positively with SAA.

CONCLUSIONS

Aa- and Cpn-infections may generate proatherogenic changes in the vascular wall by affecting the macrophage cholesterol homeostasis and endothelial function.

Possibilities for therapeutic interventions in disrupting Chlamydophila pneumoniae involvement in atherosclerosis

Strong sero-epidemiologic, pathologic, and experimental evidence suggests that Chlamydophila pneumoniae (Cpn) infection may play a causative role in the development of atherosclerosis. Cpn is an obligate intracellular gram-negative bacterium that is responsible for 10% of cases of community-acquired pneumonia. In addition to its presence in the respiratory tract, live Cpn has been found within atherosclerotic plaques. Experimental findings have established Cpn's ability to infect vascular cells and elicit important atherogenic responses. Furthermore, Cpn infection can promote atherosclerotic development in different animal models. To date however, large-scale antibiotic clinical trials have not been effective in preventing major cardiovascular events. It is becoming apparent that Cpn undergoes a persistent state of infection, which is refractory to current chlamydial antibiotics. New treatment strategies that are effective toward acute and persistent forms of Cpn infection are needed in order to effectively eradicate the bacterium within the vascular wall. Possible therapeutics targets include Cpn-specific proteins and machinery directly involved in their survival, replication and maintenance. Alternatively, selectively targeting host cell pathways and machinery required for Cpn's actions in vascular cells also represent potential treatment strategies for atherosclerosis.

Role for Porphyromonas gingivalis in the progression of atherosclerosis

An association between atherosclerosis and Porphyromonas gingivalis (P. gingivalis), a major periodontopathogen, has been shown. However, the question of whether this relationship is causal or coincidental still exist. Many individuals with evidence of atherosclerosis demonstrate seropositivity to this pathogen. Both in vitro studies and in animal models document that P. gingivalis can accelerate atheroma deposition. Recently, evidence from diverse sources has suggested P. gingivalis can activate host innate immune responses associated with atherosclerosis. These studies confirm that the inflammatory response to P. gingivalis could exacerbate vascular inflammation via secreted cytokines and/or chemokines that ultimately modulate early atherogenesis that spontaneously develop atherosclerosis. Meanwhile, the cytokine and chemokines interact in the progression of atherosclerosis. Moreover, the reaction of endothelial cells in response to P. gingivalis and its various virulence factors are diverse, the expression of chemokine differ through different signal transduction pathways accordingly. Results from these studies reinforce the connection between P. gingivalis and atherosclerosis. Given the role of P. gingivalis in the initiation and progression of atherosclerosis, attaching importance to periodontal disease may offer new therapeutic options for the management of patients with atherosclerosis.

Helicobacter pylori-induced inhibition of vascular endothelial cell functions: a role for VacA-dependent nitric oxide reduction

Epidemiological and clinical studies provide compelling support for a causal relationship between Helicobacter pylori infection and endothelial dysfunction, leading to vascular diseases. However, clear biochemical evidence for this association is limited. In the present study, we have conducted a comprehensive investigation of endothelial injury in bovine aortic endothelial cells (BAECs) induced by H. pylori-conditioned medium (HPCM) prepared from H. pylori 60190 [vacuolating cytotoxin A (Vac(+))]. BAECs were treated with either unconditioned media, HPCM (0-25% vol/vol), or Escherichia coli-conditioned media for 24 h, and cell functions were monitored. Vac(+) HPCM significantly decreased BAEC proliferation, tube formation, and migration (by up to 44%, 65%, and 28%, respectively). Posttreatment, we also observed sporadic zonnula occludens-1 immunolocalization along the cell-cell border, and increased BAEC permeability to FD40 Dextran, indicating barrier reduction. These effects were blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid (VacA inhibitor) and were not observed with conditioned media prepared from either VacA-deleted H. pylori or E. coli. The cellular mechanism mediating these events was also considered. Vac(+) HPCM (but not Vac(-)) reduced nitric oxide (NO) by >50%, whereas S-nitroso-N-acetylpenicillamine, an NO donor, recovered all Vac(+) HPCM-dependent effects on cell functions. We further demonstrated that laminar shear stress, an endothelial NO synthase/NO stimulus in vivo, could also recover the Vac(+) HPCM-induced decreases in BAEC functions. This study shows, for the first time, a significant proatherogenic effect of H. pylori-secreted factors on a range of vascular endothelial dysfunction markers. Specifically, the VacA-dependent reduction in endothelial NO is indicated in these events. The atheroprotective impact of laminar shear stress in this context is also evident.

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.

Innate immune signaling and Porphyromonas gingivalis-accelerated atherosclerosis

Periodontal diseases are a group of diseases that lead to erosion of the hard and soft tissues of the periodontium, which, in severe cases, can result in tooth loss. Anecdotal clinical observations have suggested that poor oral health may be associated with poor systemic health; however, only recently have appropriate epidemiological studies been initiated, with defined clinical endpoints of periodontal disease, to address the association of periodontal disease with increased risk for cardiovascular and cerebrovascular disease. Although conflicting reports exist, these epidemiological studies support this connection. Paralleling these epidemiological studies, emerging basic scientific studies also support that infection may represent a risk factor for atherosclerosis. With P. gingivalis as a model pathogen, in vitro studies support that this organism can activate host innate immune responses associated with atherosclerosis, and in vivo studies demonstrate that this organism can accelerate atheroma deposition in animal models. In this review, we focus primarily on the basic scientific studies performed to date which support that infection with bacteria, most notably P. gingivalis, accelerates atherosclerosis. Furthermore, we attempt to bring together these studies to provide an up-to-date framework of emerging theories into the mechanisms underlying periodontal disease and increased risk for atherosclerosis, as well as identify intervention strategies to reduce the incidence of periodontal disease in humans, in an attempt to decrease risk for systemic complications of periodontal disease such as atherosclerotic cardiovascular disease.

Increased prostanoid dependency of arterial relaxation in Chlamydia pneumoniae-infected mice

Endothelial dysfunction plays an important role in the development of atherosclerosis. Previous studies have shown that inoculation with Chlamydia pneumoniae contributes to atherosclerotic development in rabbits and hypercholesterolaemic mice and causes endothelial dysfunction in apolipoprotein E-deficient mice. The effect of acute C. pneumoniae infection on endothelial function in normocholesterolaemic C57BL/6J mice was studied by measuring the force of contraction of the descending aorta after noradrenaline stimulation and in response to methacholine-induced relaxation. In addition, the effects of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) and the cyclooxygenase inhibitor diclofenac on relaxation were assessed. Pre-treatment of the aortas with L-NAME decreased the relaxation response in both the infected and uninfected groups and no significant difference was detected between these groups, whereas diclofenac significantly attenuated the relaxation response only in the infected animals. In conclusion, infection shifted the balance of endothelium-derived relaxing factors from nitric oxide towards vasorelaxing prostanoids in C57BL/6J mice.

The possible association of Chlamydia pneumoniae infection with nasal polyps

The objective of this study was to investigate the possible etiologic role of Chlamydia pneumoniae infection in nasal polyps. This prospective clinical study was undertaken enrolling 30 patients with nasal polyps, and 30 age and sex-matched control subjects from whom epithelial material was obtained during endoscopic surgery. IgG specific ELISA was used to determine seropositivity, and indirect immunoflorescence to determine C. pneumoniae in the biopsy material. C. pneumoniae specific IgG antibodies were found to be positive in 16 (53.3%) of the patients with nasal polyps, and 9 (22%) of the control subjects (P = 0.065). Indirect immunofluorescence results indicate that there was a significant difference between groups; 16 (53.3%) patients in the study group and 8 (26.6%) patients in the control group were found to be positive (P = 0.034). We found no correlation with cigarette smoking. Our results indicated that Chlamydia pneumoniae is possibly associated with the presence of nasal polyps. However, these results remain to be confirmed with further studies using other techniques, and the underlying mechanism should be defined.

Infection and early atherosclerosis: does the evidence support causation?

Although clinical manifestations of atherosclerotic coronary heart disease occur in adult life, the initial stages of its development commence in childhood. Therefore, elucidating the pathogenesis of early atherosclerosis and identifying the network of risk factors have become fundamental priorities for both cardiovascular healthcare providers and scientists. There is mounting evidence from both human studies and animal experiments that infectious pathogens could be implicated in atherosclerosis development. The vulnerability of the arterial wall to the adverse effects of infection is probably augmented when additional risk factors and/or certain proatherogenic genetic profiles are also present. The precise mechanisms whereby infection, alone or in synergy with conventional cardiovascular risk factors, could contribute to atherosclerosis are not fully understood.

CONCLUSION

Injury to the vascular endothelium, which could be elicited by infection through inflammatory, metabolic, autoimmune, and pathogen-related mechanisms, might be a central link between infection and early atherosclerosis.

High prevalence of Chlamydia pneumoniae antibodies and increased high-sensitive C-reactive protein in patients with vascular dementia

OBJECTIVES

To determine the relationships between Chlamydia pneumoniae infection, carotid atherosclerosis, and dyslipidemia in patients with vascular dementia (VaD) and Alzheimer's disease (AD).

DESIGN

Case control study.

SETTING

Showa University Karasuyama Hospital, Tokyo, Japan.

PARTICIPANTS

One hundred twenty-four elderly subjects: 31 with VaD, 61 with AD, and 32 age-matched controls without dementia.

MEASUREMENTS

Presence of antibodies to C. pneumoniae (immunoglobulin G (IgG) and IgA), the serum concentrations of high-sensitive C-reactive protein (hs-CRP) and atherogenic lipoproteins, and the carotid artery intima-media thickness (IMT) and plaques were determined.

RESULTS

Age; body mass index; systolic and diastolic blood pressures; and fasting plasma glucose, hemoglobin A(1c), high-density lipoprotein cholesterol, and apolipoprotein A-I, B, and E concentrations did not differ significantly between the three groups, but the mean IMT and frequency of atherosclerotic plaques in the carotid arteries, as well as the serum concentrations of low-density lipoprotein cholesterol (LDL-C), lipoprotein(a), and lipid peroxides were significantly greater in VaD patients than in AD patients or nondemented controls. Hs-CRP concentrations and prevalence of C. pneumoniae IgG and IgA antibodies also were significantly higher in VaD patients than in AD patients and nondemented controls. Multiple logistic regression analysis revealed that carotid IMT and plaques, LDL-C, lipid peroxides, hs-CRP, and IgG and IgA C. pneumoniae seropositivity were independent risk factors for VaD.

CONCLUSION

These results suggest that carotid atherosclerosis, atherogenic lipoproteins, and C. pneumoniae infection (as documented by the IgG and IgA seropositivity together with increased hs-CRP) may be VaD risk factors.

Arterial endothelial injury due to infection in childhood: ticking bomb or innocent bystander?

Atherosclerosis is regarded as a chronic disease that begins in early life. While the main underlying mechanism of atherosclerosis is nowadays unequivocally attributed to a low-grade inflammatory reaction, the spectrum of aetiological conditions is far from being fully elucidated. Both viruses and bacteria have been suggested to intervene at various stages of atherosclerosis development, although a clear pathogenic link between infection and atherosclerosis remains debatable. As one key event in atherogenesis involves a perturbation of the protective mechanisms normally posed by the arterial endothelium, a number of studies have enquired into the possible detrimental effects of microbes and their components on the endothelial cells. This review aims to scrutinize the current literature in this regard, and to suggest several possible directions for future studies.