Effect of azithromycin on murine arteriosclerosis exacerbated by Chlamydia pneumoniae

Chlamydia pneumoniae infection can exacerbate atherosclerosis in animals. To test the hypothesis that antibiotic therapy inhibits the atherogenic effects of C. pneumoniae infection, 10-week-old apolipoprotein E (ApoE) null mice were infected with C. pneumoniae or placebo, were treated for 2 weeks after infection with azithromycin or placebo, and were killed at 20 weeks of age. Infection did not affect the size of the aortic lesion, and antibiotic treatment had no effect. Another group of mice, 12-week-old ApoE mice, were infected with C. pneumoniae or placebo, were treated for 2 weeks after infection with azithromycin or placebo, and were killed at 26 weeks of age. C. pneumoniae infection increased the size of the lesion in infected mice, but azithromycin did not reduce the size of the aortic lesion in infected mice. Therefore, immediate therapy of acute infection may be necessary to prevent the proatherogenic effects of C. pneumoniae infection.

Chlamydia pneumoniae and the lung

Chlamydia pneumoniae is a frequently occurring respiratory pathogen affecting all age groups. It may cause 5-20% of community-acquired pneumonias in adults and children. The organism has also been implicated as an infectious trigger for asthma. Furthermore, new studies suggest that it may play a role in the pathogenesis of several chronic diseases including atherosclerosis. However, despite the growing significance of C. pneumoniae as a pathogen, progress is hampered by the lack of standardized diagnostic methods including serology and polymerase chain reaction. This makes it practically impossible for the practitioner to make a specific microbiological diagnosis. The lack of standardized methods has also had an adverse effect on treatment trials. The dependence on serology for diagnosis in treatment studies has generated some questionable results. Unless cultures are performed, microbiological efficacy cannot be assessed and it may never be possible to survey for or document the emergence of resistance.

[Inflammation, infection and coronary artery disease: myths and realities. Special XXXV Conference of the National Congress of the Spanish Society of Cardiology]

In the past decades it has become apparent that inflammation plays a role in atherogenesis and rapid coronary artery disease progression. Active, or vulnerable, atheromatous plaques are responsible for acute coronary events and contain high concentrations of inflammatory cells as well as molecules involved in the inflammatory process, such as cytokines, adhesion molecules and growth factors. From a clinical perspective, early detection of these plaques may prevent the occurrence of serious coronary events. Unfortunately, current diagnostic techniques -i.e. angiography- do not allow the characterization of events taking place in the arterial wall. Therefore, these diagnostic tools cannot identify vulnerable plaques. Recent studies have suggested that markers of systemic inflammation may help in the detection of high risk patients. Although the role of inflammation in the pathogenesis of atherosclerosis is established, it is not known what triggers inflammation in this context. Infectious agents such as viruses and Gram negative bacteria -i.e. Chlamydia pneumoniae- have been postulated to play a role. Several mechanisms, involving inflammation and immunological processes, have been suggested to explain how chronic infections may cause atherosclerosis. Small pilot studies have also been carried out which suggest a causal role of infection in coronary artery disease. These results, however, await confirmation by other large, currently ongoing, studies. The infectious hypothesis of atherosclerosis is still a matter of debate; however, this theory has contributed to the rapid advance of our knowledge regarding the pathogenesis of coronary artery disease in the past few years. Moreover, the notion that coronary artery disease can be considered to be an inflammatory condition in its own right has opened new and challenging avenues for research.

[Impact of Chlamydia pneumoniae infections on asthma]

VIRUSES AND BACTERIA: The fact that the airways are exposed to a large number of infectious agents could explain the frequency of respiratory infections and their causal effect in bronchial inflammation. Viruses are most often the causal agent, but the frequency of bacterial infections make them potential candidates in certain respiratory diseases. Chlamydia are particularly important due to their capacity to provoke immune dysfunction and chronic inflammation. EFFECT ON ASTHMA: It is not surprising to find biological evidence of Chlamydia pneumoniae infection in a large number of subjects who experience major degradation of their asthma because asthmatic subjects are particularly susceptible to respiratory infections and Chlamydia pneumoniae is a frequent cause of such infections. PATHOGENIC EFFECT: Finding Chlamydia pneumoniae as the causal agent in asthma is however much more surprising, with a much different consequence. There are however many epidemiological and clinical findings and case observations (Chlamydia pneumoniae asthma associations, prolonged favorable course in certain obstructive bronchial diseases after a short antibiotic regimen) as well as provocative pathophysiological data favoring this particular form of "infectious asthma".

FURTHER INFORMATION

Large-scale studies with rigorous methodology remain to be performed. The would be needed to determine the exact relationship between Chlamydia pneumoniae infections and certain types of asthma, particularly when wheezing occurs after a respiratory infection and when chronic obstruction develops. The could also determine the role of anti-Chlamydia pneumoniae antibiotics in case of obstructive respiratory failure and also determine their efficacy on long-term outcome.

Antibiotic therapy for treatment of Chlamydia to prevent coronary heart disease events

Evidence is mounting that infectious agents might be involved in atherosclerosis. Therefore, antibiotic therapy might be helpful in its prevention. Early pilot therapeutic trials have targeted Chlamydia pneumoniae because it has the most evidence associating it with atherosclerosis. Small, randomized pilot trials that test the effect of macrolide therapy on future clinical events in patients with coronary artery disease have already shown promising but mixed results. Large clinical trials are presently underway that should provide more definitive information regarding the use of antibiotics in coronary artery disease. Until the results of these studies are available, it is not recommended that antibiotic therapy be routinely utilized for the treatment or prevention of complications of atherosclerosis.