The failure of antibiotics to prevent heart attacks

Gut Microbiota and Coronary Artery Disease: Current Therapeutic Perspectives

The human gut microbiota is the community of microorganisms living in the human gut. This microbial ecosystem contains bacteria beneficial to their host and plays important roles in human physiology, participating in energy harvest from indigestible fiber, vitamin synthesis, and regulation of the immune system, among others. Accumulating evidence suggests a possible link between compositional and metabolic aberrations of the gut microbiota and coronary artery disease in humans. Manipulating the gut microbiota through targeted interventions is an emerging field of science, aiming at reducing the risk of disease. Among the interventions with the most promising results are probiotics, prebiotics, synbiotics, and trimethylamine N-oxide (TMAO) inhibitors. Contemporary studies of probiotics have shown an improvement of inflammation and endothelial cell function, paired with attenuated extracellular matrix remodeling and TMAO production. Lactobacilli, Bifidobacteria, and Bacteroides are some of the most well studied probiotics in experimental and clinical settings. Prebiotics may also decrease inflammation and lead to reductions in blood pressure, body weight, and hyperlipidemia. Synbiotics have been associated with an improvement in glucose homeostasis and lipid abnormalities. On the contrary, no evidence yet exists on the possible benefits of postbiotic use, while the use of antibiotics is not warranted, due to potentially deleterious effects. TMAO inhibitors such as 3,3-dimethyl-1-butanol, iodomethylcholine, and fluoromethylcholine, despite still being investigated experimentally, appear to possess anti-inflammatory, antioxidant, and anti-fibrotic properties. Finally, fecal transplantation carries conflicting evidence, mandating the need for further research. In the present review we summarize the links between the gut microbiota and coronary artery disease and elaborate on the varied therapeutic measures that are being explored in this context.

Mechanisms, therapeutic implications, and methodological challenges of gut microbiota and cardiovascular diseases: a position paper by the ESC Working Group on Coronary Pathophysiology and Microcirculation

The human gut microbiota is the microbial ecosystem in the small and large intestines of humans. It has been naturally preserved and evolved to play an important role in the function of the gastrointestinal tract and the physiology of its host, protecting from pathogen colonization, and participating in vitamin synthesis, the functions of the immune system, as well as glucose homeostasis and lipid metabolism, among others. Mounting evidence from animal and human studies indicates that the composition and metabolic profiles of the gut microbiota are linked to the pathogenesis of cardiovascular disease, particularly arterial hypertension, atherosclerosis, and heart failure. In this review article, we provide an overview of the function of the human gut microbiota, summarize, and critically address the evidence linking compositional and functional alterations of the gut microbiota with atherosclerosis and coronary artery disease and discuss the potential of strategies for therapeutically targeting the gut microbiota through various interventions.

The intestinal microbiota and cardiovascular disease

The intestinal microbiota of human hosts is the community of microorganisms living in the small and, mainly, the large intestine of humans. This microbial ecosystem has co-evolved with humans across the millennia, has come to play an important interactive role in human physiology and has been aptly called our forgotten organ. Significant properties of the microbiota benefiting its host include energy harvest from food sources indigestible by humans, protection from pathogen colonization, and vitamin synthesis. Mounting evidence has linked changes in the composition or metabolic profiles of the microbiota with human disease, including disorders of the cardiovascular spectrum. Although cause and effect mechanisms are as yet essentially unproven in the relevant literature, the established associations point to the importance of the microbiota in the pathophysiology of cardiovascular disease (CVD). In this review, we first summarize key information on the gut microbial communities and the elaborate tools developed to analyse their structure and metabolic functions. Ecological terms are explained and analytical techniques are simplified, to enhance the understanding of published studies. Statistical methods used in microbial analysis are also described in simple terms. We then present published literature on the association of the compositional and functional changes of the microbiota with CVD, including heart failure, hypertension, and atherosclerosis. Each section of the review deals with the underlying pathophysiology of the relevant associations, connecting the observational and mechanistic aspects. Finally, we discuss the challenges that remain to be met before this field of research can generate knowledge which can impact everyday clinical practice.

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.

Observations on Chlamydia trachomatis and other microbes in reactive arthritis

There are problems in attributing causality in inflammatory arthritis. So far as C. trachomatis and sexually acquired reactive arthritis are concerned, there is much in favour of a causal relationship, although there are important caveats which need to be explored before it is possible to say unreservedly that C. trachomatis plays a causative role in reactive arthritis. For example, micro-organisms have never been cultured from synovial effusions in early disease, and only once has substantial benefit of antimicrobial treatment been reported. The claim that ocular strains of C. trachomatis are of over-riding importance in pathogenesis needs confirmation before it can be accepted. No conclusion can be made about the possibility of other small intracellular bacteria in joints having a role in causing disease. However, if it can be shown that eradication of the micro-organism, which may be difficult to prove, coincides with clinical recovery, it would go some way to recognising causality. In spite of the recognised difficulties, antibiotic studies have an important role in identifying aetiology. They need to focus on very early disease and on eradication of intra-articular bacteria. Treatment of established disease is likely to be less informative. Although a combination of antibiotics might have a future in treating established disease, diagnosing and treating non-gonococcal urethritis as soon as possible should be the aim in order to prevent the development of reactive arthritis.

Inflammatory Disease Processes and Interactions with Nutrition

Inflammation is a stereotypical physiological response to infections and tissue injury; it initiates pathogen killing as well as tissue repair processes and helps to restore homeostasis at infected or damaged sites. Acute inflammatory reactions are usually self-limiting and resolve rapidly, due to the involvement of negative feedback mechanisms. Thus, regulated inflammatory responses are essential to remain healthy and maintain homeostasis. However, inflammatory responses that fail to regulate themselves can become chronic and contribute to the perpetuation and progression of disease. Characteristics typical of chronic inflammatory responses underlying the pathophysiology of several disorders include loss of barrier function, responsiveness to a normally benign stimulus, infiltration of inflammatory cells into compartments where they are not normally found in such high numbers, and overproduction of oxidants, cytokines, chemokines, eicosanoids and matrix metalloproteinases. The levels of these mediators amplify the inflammatory response, are destructive and contribute to the clinical symptoms. Various dietary components including long chain ω-3 fatty acids, antioxidant vitamins, plant flavonoids, prebiotics and probiotics have the potential to modulate predisposition to chronic inflammatory conditions and may have a role in their therapy. These components act through a variety of mechanisms including decreasing inflammatory mediator production through effects on cell signaling and gene expression (ω-3 fatty acids, vitamin E, plant flavonoids), reducing the production of damaging oxidants (vitamin E and other antioxidants), and promoting gut barrier function and anti-inflammatory responses (prebiotics and probiotics). However, in general really strong evidence of benefit to human health through anti-inflammatory actions is lacking for most of these dietary components. Thus, further studies addressing efficacy in humans linked to studies providing greater understanding of the mechanisms of action involved are required.

Cultivation and laboratory maintenance of Chlamydia pneumoniae

Chlamydiae are Gram-negative obligate intracellular parasites. Chlamydia pneumoniae is a human respiratory pathogen that causes pneumonia, bronchitis, sinusitis, and pharyngitis. C. pneumoniae has also been associated with cardiovascular disease. C. pneumoniae can only be grown in cell culture and is more difficult to isolate from specimens than Chlamydia trachomatis. Commonly used cell lines for isolation of C. trachomatis are not sensitive for C. pneumoniae. The most sensitive cell lines for isolation of C. pneumoniae are HL and HEp-2. Centrifugation of the inoculum onto the monolayer and inclusion of cycloheximide in the medium enhance isolation. Inclusions are smaller than those of other chlamydiae and are visualized by staining with FITC-conjugated genus- or C. pneumoniae-specific monoclonal antibodies. Slow expansion and use of a small inoculum are key to successful culture. Infectious organisms can be purified by use of Hypaque-76 gradients to titers >1 x 10(8)/ml.

Multiple inflammatory markers in patients with significant coronary artery disease

BACKGROUND

Several inflammatory biomarkers are linked to cardiovascular risk. In order to investigate their coexistence and relative responses, several established and two novel markers (lactoferrin and the terminal complement complex), representing infection and central components of inflammation, were measured simultaneously in patients undergoing first-time coronary angiography.

METHODS AND RESULTS

Blood samples from patients with (n=131) or without (n=103) significant coronary artery stenosis were analyzed for plasma markers representing endothelium, platelets, neutrophils, monocytes, and complement, C-reactive protein, and antibodies against the infectious agents Chlamydia pneumoniae, Helicobacter pylori, and cytomegalovirus. In multivariate logistic regression analysis, hypercholesterolemia (p<0.001), increased concentrations of the neutrophil activation marker lactoferrin (p<0.001) and the monocyte activation marker neopterin (p=0.012), lower concentrations of the terminal complement complex (p<0.001), and antibodies against C. pneumoniae (p=0.023) were variables linked to coronary artery stenosis. In univariate analysis additional relationships were found to current smoking (p<0.001), increased plasma concentrations of vascular cell adhesion molecule-1 (p=0.015), E-selectin (p<0.01), myeloperoxidase (p=0.051) and endothelin-1 (p=0.053), as well as diabetes (p=0.039).

CONCLUSIONS

Activation of multiple inflammatory pathways and C. pneumoniae infection may influence the inflammatory response in atherosclerosis. These pilot data provide an indication of the relative usefulness of various inflammatory biomarkers, indicating that the novel markers lactoferrin and the terminal complement complex warrant further investigation.

Randomised placebo controlled multicentre trial to assess short term clarithromycin for patients with stable coronary heart disease: CLARICOR trial

OBJECTIVE

To determine if the macrolide clarithromycin affects mortality and cardiovascular morbidity in patients with stable coronary heart disease.

DESIGN

Centrally randomised multicentre trial. All parties at all stages were blinded. Analyses were by intention to treat.

SETTING

Five Copenhagen University cardiology departments and a coordinating centre.

PARTICIPANTS

13,702 patients aged 18 to 85 years who had a discharge diagnosis of myocardial infarction or angina pectoris in 1993-9 and alive in August 1999 were invited by letter; 4373 were randomised.

INTERVENTIONS

Two weeks' treatment with clarithromycin 500 mg/day or matching placebo.

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. Trial registration ClinicalTrials.gov NCT00121550.