Chlamydia pneumoniae-atherosclerosis link: a sound concept in search for clinical relevance

Bacterial Infections and Atherosclerosis – A Mini Review

Atherosclerosis is the most challenging subsets of coronary artery disease in humans, in which risk factors emerge from childhood, and its prevalence increases with age. Experimental research demonstrates that infections due to bacteria stimulate atherogenic events. Atherosclerosis has complex pathophysiology that is linked with several bacterial infections by damaging the inner arterial wall and heart muscles directly and indirectly by provoking a systemic pro-inflammation and acute-phase protein. Repeated bacterial infections trigger an inflammatory cascade that triggers immunological responses that negatively impact cardiovascular biomarkers includes triglycerides, high-density lipoprotein, C-reactive protein, heat shock proteins, cytokines, fibrinogen, and leukocyte count. Herein, we intended to share the role of bacterial infection in atherosclerosis and evaluate existing evidence of animal and human trials on the association between bacterial infections and atherosclerosis on update.

Extrinsic and Intrinsic Responses in the Development and Progression of Atherosclerosis

Atherosclerosis is a multifactorial disease that is thought to be primarily inflammatory in origin. Given the contribution of inflammation to the development and progression of atherosclerosis, other conditions that are characterised by a dysregulated inflammatory response have also been proposed to play a role. The purpose of this review is to organise and present the various inflammatory processes that can affect atherosclerosis into two broad categories: extrinsic or host-independent and intrinsic or host-dependent. Within these two categories, we will discuss various processes that may contribute to the development and progression of atherosclerosis and the clinical studies describing these associations. Although the clinical trials investigating anti-inflammatory therapies have to date provided mixed results, further studies, particularly in conjunction with lipid-lowering and blood pressure lowering therapies should be considered.

Trophoblast infection with Chlamydia pneumoniae and adverse pregnancy outcomes associated with placental dysfunction

OBJECTIVE

We sought to determine whether Chlamydia pneumoniae impairs invasive trophoblast function and is associated with preeclampsia.

STUDY DESIGN

We conducted cell viability and invasion assays using primary extravillous trophoblast cells isolated from first-trimester placentas. We performed a case-control study to identify C pneumoniae in trophoblast cells dissected by laser capture microscopy from placentas in women with severe preeclampsia and control subjects who delivered at term.

RESULTS

Trophoblast cell viability and invasion through extracellular matrices were decreased after infection with C pneumoniae (both P < .05). C pneumoniae DNA was detected in trophoblast cells in 15/48 cases but only 3/30 controls (odds ratio, 4.1; P = .02). Positive and negative controls yielded expected results.

CONCLUSION

C pneumoniae infection can reduce trophoblast invasion into the uterine wall and is associated with preeclampsia. Further investigation of the mechanisms by which C pneumoniae induces trophoblast dysfunction, and the identification of therapies to prevent adverse outcomes attributed to trophoblast dysfunction, are warranted.

Evaluation of CSF-Chlamydia pneumoniae, CSF-tau, and CSF-Abeta42 in Alzheimer's disease and vascular dementia

The potential role of microbiological factors such as Chlamydia pneumoniae (ChP) in the pathogenesis of neurodegenerative disorders, including Alzheimer's disease (AD) and vascular dementia (VD), has been suggested, but the correctness of this hypothesis still needs to be tested. In this study the appearance of ChP in the cerebrospinal fluid (CSF) of 57 AD and 21 VD patients and in 47 controls (CG) as well as the influence of ChP on the levels of tau protein and Abeta42 were investigated. The frequency of ChP occurrence in the AD patient group (43.9%) was significantly higher (p < 0.001) than in the control group (10.6%). In the case of VD patients, 9.5% of this group was positive for ChP. The presence of ChP DNA in the CSF of patients with AD significantly increases the occurrence of this disease (odds ratio = 7.21). Cerebrospinal fluid Abeta42 levels were significantly lower in patients with AD than in the CG (p < 0.001). Cerebrospinal tau protein was significantly higher in AD vs. CG (p = 0.007). However, no relationships between the presence of the bacterium in CSF and the level of either tau or Abeta42 protein were observed. In conclusion, we may suspect that testing for the presence of ChP in CSF, along with the tau and Abeta42 markers, may be used in the clinic diagnosis of AD.

TLR2 transmodulates monocyte adhesion and transmigration via Rac1- and PI3K-mediated inside-out signaling in response to Porphyromonas gingivalis fimbriae

We present evidence for a novel TLR2 function in transmodulating the adhesive activities of human monocytes in response to the fimbriae of Porphyromonas gingivalis, a pathogen implicated in chronic periodontitis and atherosclerosis. Monocyte recruitment into the subendothelium is a crucial step in atherosclerosis, and we investigated the role of P. gingivalis fimbriae in stimulating monocyte adhesion to endothelial cells and transendothelial migration. Fimbriae induced CD11b/CD18-dependent adhesion of human monocytes or mouse macrophages to endothelial receptor ICAM-1; these activities were inhibited by TLR2 blockade or deficiency or by pharmacological inhibitors of PI3K. Moreover, this inducible adhesive activity was sensitive to the action of Clostridium difficile toxin B, but was not affected by Clostridium botulinum C3 exoenzyme, pertussis toxin, or cholera toxin. Accordingly, we subsequently showed through the use of dominant negative signaling mutants of small GTPases, that Rac1 mediates the ability of fimbria-stimulated monocytes to bind ICAM-1. A dominant negative mutant of Rac1 also inhibited the lipid kinase activity of PI3K suggesting that Rac1 acts upstream of PI3K in this proadhesive pathway. Furthermore, fimbriae stimulated monocyte adhesion to HUVEC and transmigration across HUVEC monolayers; both activities required TLR2 and Rac1 signaling and were dependent upon ICAM-1 and the high-affinity state of CD11b/CD18. P. gingivalis-stimulated monocytes displayed enhanced transendothelial migration compared with monocytes stimulated with nonfimbriated isogenic mutants. Thus, P. gingivalis fimbriae activate a novel proadhesive pathway in human monocytes, involving TLR2, Rac1, PI3K, and CD11b/CD18, which may constitute a mechanistic basis linking P. gingivalis to inflammatory atherosclerotic processes.

Atrial Fibrillation Ablation: Reaching the Mainstream

INTRODUCTION AND AIMS

Ablation of atrial fibrillation (AF) has evolved rapidly in the decade since its inception. We aimed to review the results of this evolution as reflected in the published literature.

METHODS

Publications through 2005 were reviewed, and data included if there was information on the technique used, and follow-up of at least 6 months.

RESULTS

More than 23,000 patients met criteria for inclusion. There has been a steady improvement in reported outcomes (P<0.001). Variations on radiofrequency catheter ablation for pulmonary vein isolation result in apparent elimination ("cure") or improvement of AF in 75%, and surgical techniques are even better.

CONCLUSIONS

Catheter ablation of AF is now a mainstream procedure. Continuing technical advances are needed to achieve better results with more uniformity and reduced procedure times.

Infección previa por Chlamydia pneumoniae y pronóstico a largo plazo en pacientes con síndrome coronario agudo sin elevación del segmento ST

BACKGROUND AND OBJECTIVE

Contradictory data exists from case-control studies and in patients with stable coronary artery disease on the association of prior exposure to Chlamydia pneumoniae and cardiovascular events. We underwent a prospective study to investigate the prognostic value of C. pneumoniae seropositivity in patients with acute coronary syndromes.

PATIENTS AND METHOD

In a prospective cohort of 259 consecutive patients (194 men and 65 women), mean age 65 (10 years) with non-ST elevation acute coronary syndromes, we measured serum levels of IgG antibodies directed against C. pneumoniae.

RESULTS

After a mean follow-up of 28 (25, 29) months, the incidence of cardiovascular death or myocardial infarction was of 15% in seropositive patients versus 13% in seronegatives at IgG titers (1:64 (p=0.58); of 14% versus 14% at IgG titers > or = 1:128 (p=0.96); and of 14% versus 15% at IgG titers (1:256 (p=0.82). The relative risks (RR, 95% CI) of these major cardiac events adjusted for possible confounding factors were 1.11 (0.52-2.40); 1.01 (0.52-1.96); and 0.94 (0.48-1.87) respectively.

CONCLUSIONS

Chlamydia pneumoniae IgG seropositivity is not associated with a higher incidence of death or myocardial infarction in patients with non-ST segment elevation acute coronary syndromes.

New and emerging theories of cardiovascular disease: infection and elevated iron

Heart disease is the leading cause of death in both men and women in industrialized countries. Despite the tremendous gains made in decreasing the number of deaths due to cardiovascular disease, it still is health care's greatest challenge. Traditional risk factors account for only 50% of the incidence of cardiac disease. In fact, many individuals who develop heart disease have normal cholesterol and blood pressure levels. This suggests that other less well-studied risk factors may also play a role. The purpose of this report is to examine the role that recently suggested risk factors may play in the development of heart disease: coronary artery infection, specifically from Chlamydia pneumoniae, and elevated iron levels. Both initiate an inflammatory response, which might explain the elevated C-reactive protein levels frequently found in those who suffer from cardiac disease.

Genomic, serologic, and clinical case-control study of Chlamydia pneumoniae and peripheral artery occlusive disease

OBJECTIVES

Chlamydia pneumoniae has been related to atherosclerotic disease in both seroepidemiologic and genomic studies. We performed a case-control study to determine seropositivity and DNA detection in arteries of patients with peripheral artery occlusive disease and of healthy subjects.

METHODS

The study included 64 patients with peripheral artery occlusive disease, and 50 control subjects who underwent varicose vein surgery, matched to the patient group for age, sex, and tobacco use. The fibrinogen level in all study subjects was measured as a marker of inflammation. Blood samples were taken from all subjects for determination of immunoglobulin (Ig) G elementary bodies (EB) against C pneumoniae with microimmunofluorescence (MIF) and enzyme-linked immunosorbent assay (ELISA), and of IgA EB with ELISA. The cutoff titers were 1:32 for MIF and 1.1 for ELISA. Biopsy specimens of arterial atheromatous plaque were obtained from patients, and of pudendal artery and saphenous vein from control subjects, and were studied with hemi-nested polymerase chain reaction.

RESULTS

There were no differences in fibrinogen level between patients and controls. The prevalence of IgG anti-EB with MIF was 78% in patients and 24% in control subjects (P =.0001; odds ratio [OR], 11.3; 95% confidence interval [CI], 4.7-27.2). Prevalence of IgG anti-EB with ELISA was 75% in patients and 16% in control subjects (P =.0001; OR, 15.7; 95% CI, 6.1-40). There were no differences in IgA anti-EB titers. Bacterial DNA was detected in 67% of atheromatous plaques versus 12% of pudendal arteries (P =.0001) and 4% of saphenous veins. A weak correlation was found between seropositivity and the presence of intravascular DNA.

CONCLUSIONS

Our results support the hypothesis that C pneumoniae is related to the pathogenesis of atherosclerotic peripheral artery occlusive disease.

CLINICAL RELEVANCE

This study explored the infectious hypothesis in the context of the pathogenesis of atherosclerosis. This hypothesis has been supported by findings that certain infectious agents can cause or accelerate the course of diseases in which the possibility of a microbial cause was not previously proposed, as in the case of peptic ulcer and spongiform encephalopathy. The present study demonstrated the presence of Chlamydia pneumoniae and seropositivity in atheromatous plaques in patients with peripheral artery occlusive disease. These results contribute to a body of research that is opening up the possibility of treating atherosclerotic disease with antibiotic agents, and preventing it with immunization.

No evidence of involvement of Chlamydia pneumoniae in severe cerebrovascular atherosclerosis by means of quantitative real-time polymerase chain reaction

BACKGROUND AND PURPOSE

All studies reporting high numbers of Chlamydia pneumoniae DNA positives in stroke patients published to date have used polymerase chain reaction (PCR) techniques highly prone to generate false-positive results. The aim of this study was to analyze the prevalence of C. pneumoniae DNA in plaques of the carotid artery as well as in peripheral blood by means of a new, closed, real-time PCR system.

METHODS

Carotid endarterectomy specimens and preoperative peripheral blood mononuclear cells (PBMC) of 75 individuals with severe cerebrovascular atherosclerosis were analyzed by means of a C. pneumoniae-specific quantitative ompA-based real-time PCR TaqMan system. Plaques were also cultured onto HEp-2 cells. Before the surgical intervention, C. pneumoniae-specific IgM, IgG, and IgA as well as C-reactive protein (CRP) levels were determined.

RESULTS

89% of all patients studied had C. pneumoniae-specific antibodies, but the pathogen was not detected in a single carotid atheroma by real-time PCR and cell culture. However, C. pneumoniae DNA was detected in 4 PBMC samples (5.3%) at very low levels (<1 inclusion/6 mL EDTA blood). No statistical significance was found between symptomatic/asymptomatic patients, C. pneumoniae PCR, results and CRP values after correction for multiplicity-of-test adjustment.

CONCLUSIONS

By means of a closed, highly sensitive, and specific real-time PCR, C. pneumoniae was not detected in cerebrovascular atherosclerosis. PCR on PBMC was not predictive for endovascular chlamydia infection and most likely stem from previous C. pneumoniae respiratory tract infection in individual cases.

Inflammation, infection, and aortic valve sclerosis

Atherosclerosis-related mechanisms, including inflammation and possibly infection, are likely to be involved in the pathogenesis of calcific aortic valve disease. The purpose of this study was to examine whether systemic inflammatory markers and Chlamydia pneumoniae seropositivity are associated with aortic valve sclerosis (AVS) in a sample of the general population. Transesophageal echocardiography was performed in 381 subjects (median age: 67 years, range: 51-101; 52% men), a sample of the adult population in Olmsted County, Minnesota. The associations between systemic inflammatory markers (blood counts, including white blood cells differential counts, fibrinogen, and high-sensitivity C-reactive protein [hs-CRP]), C. pneumoniae immunoglobulin G (IgG) antibody titers, and AVS were examined. AVS was present in 140 subjects (37% of the population). After adjustment for age, sex, and smoking status: (1). hs-CRP was associated with AVS (odds ratio: 1.20 per two-fold increase in hs-CRP; 95% confidence interval: 1.01-1.43; P = 0.04) but this association was not significant after adjustment for additional risk factors for AVS, including body mass index (P = 0.52). (2). Blood counts and fibrinogen were not associated with AVS (P-values >0.30). (3). C. pneumoniae IgG antibody titers (low [1:16-1:32], intermediate [1:64-1:128], or high [>or=1:256] titers, compared with titers <1:16) were not associated with AVS (P = 0.21). In conclusion, hs-CRP is weakly associated with AVS, an association that is not independent of other AVS risk factors. Blood counts, fibrinogen, and C. pneumoniae seropositivity are not associated with AVS. These findings suggest that other non-inflammatory non-infectious mechanisms are likely to have a role in the pathogenesis of calcific aortic valve disease.

Clinical and Biochemical Results of the Metalloproteinase Inhibition with Subantimicrobial Doses of Doxycycline to Prevent Acute Coronary Syndromes (MIDAS) Pilot Trial

Background— Vulnerable plaque demonstrates intense inflammation in which macrophages secrete matrix metalloproteinases (MMPs) that degrade the fibrous cap, ultimately leading to rupture, in situ thrombosis, and an associated clinical event. Thus, inhibition of MMP activity or more general suppression of vascular inflammation are attractive targets for interventions intended to reduce plaque rupture. We hypothesized that subantimicrobial doses of doxycycline (SDD) (20 mg twice daily) would benefit patients with coronary artery disease by reducing inflammation and MMP activity and thus possibly prevent coronary plaque rupture events.

Methods and Results— We conducted a prospective, randomized, double-blind, placebo-controlled pilot study of 6 months of SDD or placebo treatment to reduce inflammation and prevent plaque rupture events. A total of 50 patients were enrolled, of whom 24 were randomized to placebo and 26 to SDD. At 6 months, there was no difference in the composite endpoint of sudden death, fatal myocardial infarction (MI), non-fatal MI, or troponin-positive unstable angina in SDD compared with placebo-treated patients (8.4% versus 0%, P =0.491). Biochemical markers of inflammation were assessed in plasma at study entry and after 6 months of therapy in 30 patients. In SDD-treated patients, high-sensitivity C-reactive protein (CRP) was reduced by 46% from 4.8±0.6 μg/mL to 2.6±0.4 μg/mL ( P =0.007), whereas CRP was not significantly reduced in placebo patients. Interleukin (IL)-6 decreased from 22.1±3.7 pg/mL at baseline to 14.7±1.8 pg/mL at 6 months in SDD-treated patients ( P =0.025) but did not decrease significantly in placebo-treated patients. On zymography, pro-MMP-9 activity was reduced 50% by SDD therapy ( P =0.011), whereas it was unchanged by placebo treatment.

Conclusion— SDD appears to exert potentially beneficial effects on inflammation that could promote plaque stability. These findings should be investigated in a larger study.

Does high plant feed magnesium and potassium protect healthy ruminants from atherosclerosis? A review

The literature data were surveyed to clarify the role of magnesium and potassium in the development of atherosclerosis (AS) in cows and the findings were compared with human data. Special attention was paid to the eastern Finland where AS is very common in humans and absent in the cattle. A hypothesis is proposed that high magnesium and potassium intakes at plant feeding protect from severe AS processes at least in cows in the absence of chronic infections. In about 1500 necropsies in calves and cows on plant feeding, neither antemortem clinical AS symptoms nor postmortal macroscopical AS were detected in the endocardium or in aorta. Also, abattoiries in endemic selenium- and vitamin E-deficient areas report that no macroscopic AS have been found in the inspected more than 400000 slaughtered cattle. In vitamin D(3) poisoned cows AS is readily detected. The milk-fed calves in magnesium deficiency experiments regularly show AS after 3 months of age. Adult ruminating cattle get daily 150-300 g potassium while the need is 35 g. During the indoor feeding period the cows suffered in eastern Finland often from carotene, vitamin E and selenium deficiencies as well as also of energy, protein, phosphorus and zinc deficiencies before grass ensiling feeding started. Endemic goiter prevalence was about 30%. Still such cows did not have AS under such unfavorable conditions. The findings support the hypothesis that the high magnesium and potassium intakes protect cows from AS.

Medical treatment of peripheral arterial disease

PURPOSE OF REVIEW

The evolution of interventional treatments of peripheral arterial disease is progressing at a dizzying pace. However, optimized medical therapy of these patients may be neglected. Recent advances in our understanding of atherosclerosis and the epidemiology of vascular disease reemphasize the importance of a consistent and complete medical regimen. They have also opened new avenues for potential therapy.

RECENT FINDINGS

A diagnosis of peripheral arterial disease confers an increased risk of morbidity and mortality that can be at least partially mitigated with a properly designed medical regimen. New evidence supports the importance of risk factor modification including controlling hypertension, lowering lipid levels, and the routine use of antiplatelet agents. For claudication symptoms, several newer drugs and the use of immune-modifying therapy are showing some improvement in symptoms. The use of gene therapy and other means to achieve improved collateral formation in ischemic tissues are showing some promise in the early stages of study.

SUMMARY

Peripheral arterial disease is a marker of cardiovascular morbidity and mortality risk. An individualized plan should be devised to include smoking cessation, exercise, lowering serum lipids, lowering high blood pressure, and daily antiplatelet therapy. Supervised exercise programs and cilostazol remain the first-line medical therapies for claudication symptoms, and anticoagulants are added to patients who have bypasses at high risk for thrombosis. The utilities of immune-modifying, antibiotic, and angiogenic therapies remain to be proven.

Recruitment of Chlamydia pneumoniae-infected macrophages to the carotid artery wall in noninfected, nonatherosclerotic mice

OBJECTIVE

Monocyte recruitment into the subendothelium is a crucial step in atherogenesis. Chlamydia pneumoniae resides in circulating monocytes and in the atherosclerotic vascular wall. However, the role of C pneumoniae for monocyte recruitment is unknown. The aim of this study was to examine the impact of C pneumoniae on monocyte adhesion and migration.

METHODS AND RESULTS

C pneumoniae-infected, fluorescence-labeled mouse macrophages (ANA-1) were injected intravenously into noninfected, healthy mice. In vivo videomicroscopy showed increased rolling and firm adhesion to the carotid artery compared with noninfected macrophages. In vitro, C pneumoniae infection (yielding 25% to 35% infected monocytes) increased adhesion of human monocytes or MonoMac6 cells to human umbilical vein endothelial cells and improved cell migration through endothelial-like ECV604 cells. Cell adhesion was inhibited by antibody blockade of very late antigen-4, lymphocyte function-associated antigen-1, macrophage antigen-1, or urokinase receptor, which were found upregulated or activated on C pneumoniae infection (flow cytometry). In contrast, C trachomatis did not induce monocyte adhesion at comparable infection rates (25% to 35%), indicating a unique activation pathway for C pneumoniae. Polymyxin B did not affect C pneumoniae-induced adhesion, excluding a relevant role of lipopolysaccharide in this process.

CONCLUSIONS

These data indicate that C pneumoniae can direct monocytes to predilection sites of nonatherosclerotic vessel walls in vivo by activation of the integrin adhesion receptor system.