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 2000’s 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 lengthy 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 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.
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)
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.
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 was 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 preinterventional 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 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.
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 continual 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.