Linkages between oral commensal bacteria and atherosclerotic plaques in coronary artery disease patients

Abstract

Coronary artery disease is an inflammatory disorder characterized by narrowing of coronary arteries due to atherosclerotic plaque formation. To date, the accumulated epidemiological evidence supports an association between oral bacterial diseases and coronary artery disease, but has failed to prove a causal link between the two. Due to the recent surge in microbial identification and analyses techniques, a number of bacteria have been independently found in atherosclerotic plaque samples from coronary artery disease patients. In this study, we present meta-analysis from published studies that have independently investigated the presence of bacteria within atherosclerotic plaque samples in coronary artery disease patients. Data were collated from 63 studies covering 1791 patients spread over a decade. Our analysis confirms the presence of 23 oral commensal bacteria, either individually or in co-existence, within atherosclerotic plaques in patients undergoing carotid endarterectomy, catheter-based atherectomy, or similar procedures. Of these 23 bacteria, 5 (Campylobacter rectus, Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella intermedia, Prevotella nigrescens) are unique to coronary plaques, while the other 18 are additionally present in non-cardiac organs, and associate with over 30 non-cardiac disorders. We have cataloged the wide spectrum of proteins secreted by above atherosclerotic plaque-associated bacteria, and discuss their possible roles during microbial migration via the bloodstream. We also highlight the prevalence of specific poly-microbial communities within atherosclerotic plaques. This work provides a resource whose immediate implication is the necessity to systematically catalog landscapes of atherosclerotic plaque-associated oral commensal bacteria in human patient populations.

Fig. 1

Schematic representation of inflammatory mechanisms involved in pathogenesis of atherosclerosis and plaque formation. LDL is retained in arterial intima via ionic interactions with endothelial cells, leading to the enzymatic oxidative modification of LDL into OxLDL. This is followed by secretion of pro-inflammatory cytokines that leads to the differentiation of monocytes into macrophages. Macrophages secrete more chemokines and mediate recruitment of neutrophils via scavenger receptors and further attract monocytes. Macrophages retained in arterial intima get converted into foam cells leading to the formation of atherosclerotic plaques

Fig. 2

a Graphical representation of the techniques used to identify the atherosclerotic plaque-associated bacteria in CAD patients. Y-axis represents the number of studies reporting the presence of bacteria in the plaque samples, while X-axis depicts the corresponding bacteria. The cohort of 23 commensal bacteria is dominated by gram-negative bacteria with the exception of Streptococcus sp., which are gram-positive. Of these 23 atherosclerotic plaque-associated bacteria, A. actinomycetemcomitans, C. rectus, E. corrodens, E. hormaechei, S. gordonii, S. mitis, S. mutans, S. oralis, S. sanguinis, H. pylori, and P. aeruginosa are facultative anaerobes, while C. pneumoniae, F. necrophorum, F. nucleatum, M. pneumoniae, P. endodontalis, P. gingivalis, P. intermedia, P. nigrescens, T. denticola, and T. forsythia are obligatory anaerobes. There are two exceptions in P. luteola (aerobe) and Veillonella (anaerobe). IF immunofluorescence, IHC immunohistochemistry, mAb monoclonal antibodies. b Atherosclerotic plaque-associated bacteria identified using 16S rRNA technique. X-axis represents the % of patients positive for the bacteria identified using 16S rRNA gene sequencing, while Y-axis represents the corresponding bacteria. Total number of study subjects vs. positive patients is mentioned on the top of graph. c Atherosclerotic plaque-associated bacteria identified using traditional PCR techniques. X-axis represents the % of patients positive for the bacteria identified using traditional PCR techniques, while Y-axis represents the corresponding bacteria. Total number of study subjects vs. positive patients is mentioned on the top of graph. d Atherosclerotic plaque-associated bacteria identified using immunofluorescence, immuno-histochemistry, and antibody screening methods. X-axis represents the % of patients positive for the bacteria identified using multiple techniques, while Y-axis represents the corresponding bacteria. Total number of study subjects vs. positive patients is mentioned on the top of graph

Fig. 3

The tissue localization of the 23 oral commensal bacteria associated with atherosclerotic plaque samples from CAD patients. Sixteen of the 23 atherosclerotic plaque-associated bacteria were not unique to atherosclerotic plaque samples and are present in multiple non-cardiac organs (gram-negative microbes are in red)

Fig. 4

Multiple diseases caused by the atherosclerotic plaque-associated bacteria. Dot plot graph for cardiac and non-cardiac diseases caused by the atherosclerotic plaque-associated oral bacteria divided into categories based on their tissue localization (prepared using GG plot)

Fig. 5

Proteins secreted by the atherosclerotic plaque-associated bacteria. a Histogram representing the number of secretory protein/peptides and proteases from atherosclerotic plaque-associated bacteria. b The gingival crevice is a habitat to many oral microbes that secrete proteins, peptides and proteases. (1) Secretory peptides and proteases are likely responsible for altering the host actin cytoskeleton in the gingival epithelium leading to microbial entry into the system. (2) These secreted proteins can also activate the immune system causing inflammation. Primarily, cytokine-mediated (IL-6 and IL-8) inflammation is associated with atherosclerotic plaque formation. Certain proteases cause inflammatory response by activating the complement system

Fig. 6

Atherosclerotic plaque-associated bacteria form biofilm structures within the atherosclerotic plaque samples. During initial phase of biofilm formation, early colonizers—Veillonella, Streptococcus, and Actinomyces—interact to establish an initial microenvironment supporting each other with the help of metabolic products. These bacteria act as a platform for the middle colonizer F. nucleatum, which then completes the biofilm formation by providing an adhering platform for the late colonizers—T. forsythia, A. actinomycetemcomitans, T. denticola, and P. gingivalis

Fig. 7

Study selection criteria to determine the population of microbes present in atherosclerotic plaques of CAD patients. Cataloguing procedure used to annotate all known oral microbes that have been identified from atherosclerotic plaque samples of CAD patients. In brief, the records present in PUBMED were studied by using combination of terminologies such as microbes, microorganism, and bacteria along with CAD, cardiovascular disease, atheroma, atherosclerosis, and atherosclerotic plaque. The articles were collated, duplicates removed, and relevant data extracted