Every year in the U.S. alone, 610,000 people die from coronary artery/heart disease (CAD). It is the leading cause of death for both men and women accounting for 1 in 4 deaths. Diet, lifestyle, and genetics determine your propensity to develop CAD, right?
The answer to this may not be as simple as we would like. Beginning in the 1990’s evidence started to mount suggesting that Chlamydia pneumoniae might be involved in both the onset and the progression of the disease. Through the mid-2000s trials were published, funded by makers of branded antibiotics (Pfizer and others) examining the impact of antibiotic therapy on CAD.
Trial Design Failure
Sadly, the studies weren’t designed with the bug in mind and they failed. Drug trials examined the sickest patients (prevention of secondary events), used a single antibiotic, and employed an intermittent or insufficient duration of treatment. C. pneumoniae has a complex, triphasic lifecycle with an “elementary body” (EB) that is impervious to any antimicrobial. It’s the infectious, non-replicating form of the organism. In addition, there is a replicating form called the “reticulate body” that is susceptible to antibiotics as well as a “cryptic body” that does not replicate and is not very susceptible to antibiotics. The cryptic body is sometimes known as an “aberrant body”. Research has shown that in order to treat CpN successfully, a combination of antibiotics is required rather than just one (like Azithromycin alone for example), and the treatment has to be long enough to address the presence of these EBs, essentially “unhatched eggs”, which convert to the active replicating form called a “reticulate body” or to the “cryptic body”. Dr. Lee Ann Campbell and Dr. Michael Rosenfeld sum up the landscape well in terms of CpN and CAD.
“…other investigators have underscored several factors that warrant critical evaluation before dismissing C. pneumoniae as a contributor to atherosclerotic processes. First, treatment was given to patients with “end stage of disease” that is likely not modifiable. By analogy, antibiotic treatment is not effective in individuals in which inflammation resulting from chronic C. trachomatis infection of the upper genital tract or eye has led to the fibrosis and scarring observed in tubal factor infertility and trachoma, respectively. Whether antibiotics would be efficacious in the treatment of patients with early atherosclerosis has not been determined as such studies would be difficult to design and execute. Second, it is possible that antibiotic treatment might be ineffective due to pathogen burden as viruses or other bacteria contributing to atherosclerotic processes may not be susceptible to the chosen antibiotics. Third, the patients in the large scale trials had advanced atherosclerosis and the events being measured were likely due to plaque destabilization and rupture, events that may be independent of plaque progression due to infection. Fourth, a single antibiotic was used in the trials and it is possible that treatment Persistent C. pneumoniae infection with a combination of antibiotics might be more effective as has been shown for patients with chronic Chlamydia-induced reactive arthritis. Last, and the focus of this opinion is the ability of Chlamydiae to establish persistent/chronic infection and the difficulty in treating such infections. Chlamydiae undergo a developmental cycle in which the elementary body, an infectious but metabolically inactive form, is not susceptible to antibiotics. The cryptic body, the intracellular non-replicating form, can establish persistence, a state in which the developmental cycle is arrested rendering the organism refractory to antibiotics.”
New trials with a more appropriate study design are desperately needed: 1) The correct combination of antibiotics to address the lifecycle of CpN. 2) The appropriate duration of therapy and 3) The patient population whose disease process isn’t beyond the point of treatments.
Clinical study of Chlamydia pneumoniae infection in patients with coronary heart disease
n=92 patients with CHD, treated with percutaneous coronary intervention (PCI), in addition, 50 healthy controls. BMC Cardiovascular Disorders, 2019.
Methods- “The incidences of CP infection and serum Chlamydia pneumoniae IgA antibody (CP-IgA), high sensitive C-reactive protein (hs-CRP), and interleukin-6 (IL-6) were compared in these two groups. The classification of coronary artery lesion, the incidence of perioperative cardiovascular events, and adverse prognosis events within six months after procedure were compared.”
Results- “The incidence of CP infection in the case group was higher (42.4% vs. 0%, P < 0.05). Furthermore, 17 patients were at grade I, 39 patients were at grade II, and 36 patients were at grade III. The incidences for these three kinds of patients were 17.6, 30.8, and 66.7%. The incidence of CP infection at grade III was higher than that of grade I or II (P < 0.05). Serum CP-IgA, hs-CRP, and IL-6 levels increased with the severity of the coronary artery disease (P < 0.05), and the serum hs-CRP and IL-6 levels of patients with perioperative cardiovascular events were higher (P < 0.05). Moreover, the serum CP-IgA levels of the patients with adverse prognosis events were also higher (P < 0.05).”
Conclusions- “Patients with coronary heart disease have a high CP infection rate. The degree of infection is relevant to the severity of the coronary artery lesions and postoperative prognosis of patients, suggesting that CP infection may be an important factor affecting the incidence and prognosis of coronary heart disease.”
Effect of Treatment for Chlamydia pneumoniae and Helicobacter pylori on Markers of Inflammation and Cardiac Events in Patients With Acute Coronary Syndromes South Thames Trial of Antibiotics in Myocardial Infarction and Unstable Angina (STAMINA)
Prospective, randomized, placebo-controlled trial, n= 325, Circulation 2002.
Methods – Acute myocardial infarction or unstable angina (acute coronary syndromes) were randomized to receive a 1-week course of 1 of 3 treatment regimens: (1) placebo; (2) amoxicillin (500 mg twice daily), metronidazole (400 mg twice daily), and omeprazole (20 mg twice daily); or (3) azithromycin (500 mg once daily), metronidazole (400 mg twice daily), and omeprazole (20 mg twice daily).
Result– At 12 weeks, there was a 36% reduction in all end points in patients receiving antibiotics compared with placebo (P=0.02). This reduction persisted during the 1-year follow-up.
Conclusion – Antibiotic treatment significantly reduced adverse cardiac events in patients with acute coronary syndromes, but the effect was independent of H pylori or C pneumoniae seropositivity.
Antibiotic Treatment of Chlamydia pneumoniae after Acute Coronary Syndrome
Prospective, randomized, placebo-controlled trial, n=4,162, NEJM 2005.
400mg gatifloxacin QD for 2 weeks, then 10 days of treatment per month for (18-32 months, mean 2 years).
Primary efficacy outcome – death from all causes, myocardial infarction, documented unstable angina that required rehospitalization, revascularization with either percutaneous coronary intervention or coronary-artery bypass surgery (if these procedures were performed at least 30 days after randomization), or stroke.
Result – no statistically significant difference between placebo and gatifloxacin groups.
Limitations – duration of antimicrobial therapy (10 day “pulses” versus continuous treatment) and the use of one antimicrobial versus combination therapy to address the various stages in the CpN life cycle and persistence of the organism.
Azithromycin for the Secondary Prevention of Coronary Events (ACES)
Randomized, double-blind, placebo-controlled trial, n=4012, NEJM 2005.
Methods- Men and women 18 years of age or older who had documented, stable coronary heart disease. Participants were randomly assigned to receive either a 600-mg azithromycin tablet or a matching placebo tablet once weekly for one year.
Result- This trial found that one year of weekly azithromycin therapy was not associated with any clinically significant benefit in the secondary prevention of coronary events.
Conclusion- this study suggests that neither C. pneumoniae nor another organism susceptible to azithromycin plays an important role in events associated with late-stage coronary heart disease.
Limitations- “Our study has several limitations, including the advanced stage of disease (described above), the possibility that the antibiotic does not reach the microorganism in the chronic lesions of atherosclerosis, the possibility that the treatment was not continued long enough or that the dose of antibiotic given was too small, and the possibility that the antibiotic was not sufficiently effective against C. pneumoniae. These limitations do not, for practical purposes, weaken the basic conclusion of this study that antibiotic treatment cannot be recommended for the treatment of chronic coronary heart disease.”
Randomized secondary prevention trial of azithromycin in patients with coronary artery disease and serological evidence for Chlamydia pneumoniae infection (ACADEMIC)
A prospective, randomized, placebo-controlled trial, n=302, Circulation 1999.
Methods- CAD patients that had a seropositive reaction to C pneumoniae (IgG titers ≥1:16) randomized to receive placebo or azithromycin, 500 mg/d for 3 days, then 500 mg/wk for 3 months.
Result- Azithromycin reduced a global rank sum score of the 4 inflammatory markers at 6 (but not 3) months (P=0.011) as well as the mean global rank sum change score: 531 (SD=201) for active drug and 587 (SD=190) for placebo (P=0.027). Specifically, change-score ranks were significantly lower for CRP (P=0.011) and IL-6 (P=0.043). Antibody titers were unchanged, and number of clinical cardiovascular events at 6 months did not differ by therapy (9 for active drug, 7 for placebo). Azithromycin decreased infections requiring antibiotics (1 versus 12 at 3 months, P=0.002) but caused more mild, primarily gastrointestinal, adverse effects (36 versus 17, P=0.003).
Conclusions- In CAD patients positive for C pneumoniae antibodies, global tests of 4 markers of inflammation improved at 6 months with azithromycin. However, unlike another smaller study, no differences in antibody titers and clinical events were observed. Longer-term and larger studies of antichlamydial therapy are indicated.
Azithromycin for the secondary prevention of coronary heart disease events: the WIZARD study: a randomized controlled trial.
Randomized, placebo-controlled trial, n = 7747, JAMA, 2003
Methods- adults with previous myocardial infarction that had occurred at least 6 weeks previously (median, 2.6 years) and a C pneumoniae IgG titer of 1:16 or more. The patients received either azithromycin (600 mg/d for 3 days during week 1, then 600 mg/wk during weeks 2-12; n = 3879) or placebo (n = 3868).
Results- After a median of 14 months of follow-up, there was no significant risk reduction in the likelihood of a primary event with azithromycin vs placebo (7% [95% confidence interval, -5% to 17%], P =.23).
Conclusion- Among stable patients with previous myocardial infarction and with evidence of C pneumoniae exposure, a 3-month course of azithromycin did not significantly reduce the clinical sequelae of coronary heart disease.
Limitations- As in previous studies, the choice of a single antimicrobial (azithromycin) versus combination therapy, and relatively short duration of treatment (3 months) may not address the persistence of the organism, Chlamydia pneumonaie.
Clarithromycin for stable coronary heart disease increases all-cause and cardiovascular mortality and cerebrovascular morbidity over 10years in the CLARICOR randomised, blinded clinical trial
Randomized, placebo-controlled trial, n=4373, International Journal of Cardiology, 2015
Methods- patients with stable coronary heart disease were randomized to 2 weeks of clarithromycin 500 mg a day versus placebo. 10 year follow up was performed through Danish public registers and analyzed with Cox regression. “Primary outcome: composite of all-cause mortality, myocardial infarction, or unstable angina pectoris during three years’ follow-up. Secondary outcome: composite of cardiovascular mortality, myocardial infarction, or unstable angina pectoris. The outcomes were obtained from Danish registers and were blindly assessed by the event committee.”
Results- “2172 participants were randomised to clarithromycin and 2201 to placebo. We found no significant effects of clarithromycin on the primary outcome (hazard ratio 1.15, 95% confidence interval 0.99 to 1.34) or secondary outcome (1.17, 0.98 to 1.40). Mortality was significantly higher in the clarithromycin arm (1.27, 1.03 to 1.54; P = 0.03) as a result of significantly higher cardiovascular mortality (1.45, 1.09 to 1.92; P = 0.01).”
Conclusions- “Short term clarithromycin in patients with stable coronary heart disease may cause significantly higher cardiovascular mortality. The long term safety of clarithromycin in patients with stable ischaemic heart disease should be examined.”
Detection of Viable Chlamydia pneumoniae in Abdominal Aortic Aneurysms
Case-control study, n=26 AAA surgical patients compared to 17 autopsy controls, European Journal of Vascular and Endovascular Surgery 2000.
Result – C. pneumoniae was detected in the aortic aneurysms of 20/26 patients by immunohistochemical analysis (IHC). C. pneumoniae was cultured from 10 of the 20 IHC-positive patients. Only 1/17 controls were positive for C. pneumoniae by IHC (p=0.0001).
Conclusion – C. pneumoniae is often present in AAAs in a viable form and that C. pneumoniae is linked to the pathogenesis of AAA.
Roxithromycin Treatment Prevents Progression of Peripheral Arterial Occlusive Disease in Chlamydia pneumoniae Seropositive Men
n= 40, randomized, double-blind, placebo-controlled trial
Methods – roxithromycin 300mg QD for 28 days versus placebo in C pneumoniae seropositive men with established PAOD.
Results – The effect of macrolide treatment on the number of interventions per patient and on pre-interventional walking distance was significant. Carotid plaque areas monitored over 6 months decreased in the roxithromycin group (mean relative value, 94.4%) but remained constant in the placebo group (100.2%). Regression of carotid plaque size observed in roxithromycin-treated patients was significant for soft plaques.
Conclusion – This study indicates that macrolide treatment for 1 month is effective in preventing C pneumoniae seropositive men from progression of lower limb atherosclerosis for several years.
Matrix metalloproteinase-9 expression is associated with the presence of Chlamydia pneumoniae in human coronary atherosclerotic plaques
n=31 coronary atherosclerotic plaque specimens, BMJ Heart 2005.
Methods – immunohistochemistry (IHC), polymerase chain reaction (PCR), and reverse transcription PCR for the presence of C pneumoniae (CpN) antigen and genomic DNA, and of MMP-9 protein and transcripts.
Results – IHC analysis identified a strong association between the presence of CpN antigen and the production of MMP-9 in coronary atherosclerotic plaques (p = 0.001). Analysis of the intralesional amount of CpN and MMP-9 indicated an increased number of cells positive for MMP-9 in arterial sections that had increased CpN positivity (p < 0.05).
Conclusion – This study provides evidence of an association between expression of MMP-9 and the intravascular presence of CpN and may suggest a potential pathological mechanism whereby CpN may contribute to the progression of coronary atherosclerosis.
n= 58 tissue culture and PCR, Journal of Medical Microbiology, 2001.
Abstract- “Samples of atherosclerotic tissue from 58 patients undergoing carotid surgery were analysed by tissue culture and PCR for Chlamydia pneumoniae; PCR was performed to detect Omp1, 16S rRNA and HSP-70 genes. To understand the active pathogenic role of C. pneumoniae, a reverse transcriptase-PCR (RT-PCR) assay was applied to detect the specific RNAs expressed either in the replicative form or in the cryptic form found in chronic infection. The C. pneumoniae omp1 gene, encoding the major outer-membrane protein (MOMP), was detected in 13 of 58 samples. Among these, the result was confirmed in 11 samples after amplification of a further target, the 16S rRNA, and the presence of the HSP-70 gene, encoding heat-shock protein 70, was revealed in only five cases. All the samples were negative for evidence of specific RNAs by RT-PCR. The presence of genomic DNA and absence of specific RNAs in atherosclerotic tissue samples suggests a lack of an active metabolic or persistent infective role for C. pneumoniae. Thus, traces of C. pneumoniae DNA in these samples could be due to a degradative pathway of the host defensive cellular and biochemical mechanisms.”
Chlamydia pneumoniae-Mediated Inflammation in Atherosclerosis: A Meta-Analysis
Mediators of Inflammation, 2015.
Abstract- “Several studies have attempted to relate the C. pneumoniae-mediated inflammatory state with atherosclerotic cardiovascular diseases, providing inconsistent results. Therefore, we performed a meta-analysis to clarify whether C. pneumoniae may contribute to the pathogenesis of atherosclerosis by enhancing inflammation. 12 case-control, 6 cross-sectional, and 7 prospective studies with a total of 10,176 patients have been included in this meta-analysis. Odds Ratio (OR) with a 95% confidence interval was used to assess the seroprevalence of C. pneumoniae and differences between levels of inflammatory markers were assessed by standard mean differences. Publication bias was performed to ensure the statistical power. hsCRP, fibrinogen, interleukin- (IL-) 6, TNF-α, and IFN-γ showed a significant increase in patients with atherosclerosis compared to healthy controls (P < 0.05), along with a higher seroprevalence of C. pneumoniae (OR of 3.11, 95% CI: 2.88-3.36, P < 0.001). More interestingly, hsCRP, IL-6, and fibrinogen levels were significantly higher in C. pneumoniae IgA seropositive compared to seronegative atherosclerotic patients (P < 0.0001). In conclusion, the present meta-analysis suggests that C. pneumoniae infection may contribute to atherosclerotic cardiovascular diseases by enhancing the inflammatory state, and, in particular, seropositivity to C. pneumoniae IgA, together with hsCRP, fibrinogen, and IL-6, may be predictive of atherosclerotic cardiovascular risk.”
Persistent C. pneumoniae infection in atherosclerotic lesions: rethinking the clinical trials
Frontiers in Cellular and Infection Microbiology, 2014.
Summary- Dr. Campbell and Dr. Rosenfeld sum up the landscape in the CAD research related to in vitro and in vivo studies. They speak about the continued isolation of Chlamydia in atherosclerotic lesions, the failure of monotherapy trials and the “why” behind it, and the effect that this had on the enthusiasm around and pursuit of the infection hypothesis in CAD. They contend that the jury is still out and more research is warranted based upon the body of evidence implicating this pathogen.
Infectious burden and atherosclerosis: A clinical issue
World Journal of Clinical Cases, 2014.
Abstract- “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.”
Chlamydia pneumoniae Infection in Atherosclerotic Lesion Development through Oxidative Stress: A Brief Overview
International Journal of Molecular Sciences, 2013.
Abstract- “Chlamydia pneumoniae, an obligate intracellular pathogen, is known as a leading cause of respiratory tract infections and, in the last two decades, has been widely associated with atherosclerosis by seroepidemiological studies, and direct detection of the microorganism within atheroma. C. pneumoniae is presumed to play a role in atherosclerosis for its ability to disseminate via peripheral blood mononuclear cells, to replicate and persist within vascular cells, and for its pro-inflammatory and angiogenic effects. Once inside the vascular tissue, C. pneumoniae infection has been shown to induce the production of reactive oxygen species in all the cells involved in atherosclerotic process such as macrophages, platelets, endothelial cells, and vascular smooth muscle cells, leading to oxidative stress. The aim of this review is to summarize the data linking C. pneumoniae-induced oxidative stress to atherosclerotic lesion development.”
Chlamydia pneumoniae and Oxidative Stress in Cardiovascular Disease: State of the Art and Prevention Strategies
International Journal of Molecular Sciences, 2014.
Abstract- “Chlamydia pneumoniae, a pathogenic bacteria responsible for respiratory tract infections, is known as the most implicated infectious agent in atherosclerotic cardiovascular diseases (CVDs). Accumulating evidence suggests that C. pneumoniae-induced oxidative stress may play a critical role in the pathogenesis of CVDs. Indeed, the overproduction of reactive oxygen species (ROS) within macrophages, endothelial cells, platelets and vascular smooth muscle cells (VSMCs) after C. pneumoniae exposure, has been shown to cause low-density lipoprotein oxidation, foam cell formation, endothelial dysfunction, platelet adhesion and aggregation, and VSMC proliferation and migration, all responsible for the typical pathological changes of atherosclerotic plaque. The aim of this review is to improve our insight into C. pneumoniae-induced oxidative stress in order to suggest potential strategies for CVD prevention. Several antioxidants, acting on multi-enzymatic targets related to ROS production induced by C. pneumoniae, have been discussed. A future strategy for the prevention of C. pneumoniae-associated CVDs will be to target chlamydial HSP60, involved in oxidative stress.”