Periodontal bacterial invasion and infection: contribution to atherosclerotic pathology.

OBJECTIVE: The objective of this review was to perform a systematic evaluation of the literature reporting current scientific evidence for periodontal bacteria as contributors to atherosclerosis. METHODS: Literature from epidemiological, clinical and experimental studies concerning periodontal bacteria and atherosclerosis were reviewed. Gathered data were categorized into seven "proofs" of evidence that periodontal bacteria: 1) disseminate from the oral cavity and reach systemic vascular tissues; 2) can be found in the affected tissues; 3) live within the affected site; 4) invade affected cell types in vitro; 5) induce atherosclerosis in animal models of disease; 6) non-invasive mutants of periodontal bacteria cause significantly reduced pathology in vitro and in vivo; and 7) periodontal isolates from human atheromas can cause disease in animal models of infection. RESULTS: Substantial evidence for proofs 1 to 6 was found. However, proof 7 has not yet been fulfilled. CONCLUSIONS: Despite the lack of evidence that periodontal bacteria obtained from human atheromas can cause atherosclerosis in animal models of infection, attainment of proofs 1 to 6 provides support that periodontal pathogens can contribute to atherosclerosis.

Klebsiella pneumoniae induces an inflammatory response in human retinal-pigmented epithelial cells.

PURPOSE: The retinal pigment epithelium (RPE) is a barrier to Klebsiella pneumoniae infection in endogenous endophthalmitis. Nevertheless, the inflammatory response of RPE cells upon interaction with this pathogen has not been studied. Here we tested the hypothesis that K. pneumoniae induces an inflammatory response in human retinal epithelial cells. METHODS: In this study we set out to investigate the effects of whole K. pneumoniae and of its lipopolysaccharide on RPE cells in vitro using bacterial invasion and cytotoxicity assays, fluorescent microscopy and ELISA. For that, we utilized K. pneumoniae strain ATCC 43816 and the continuous human retinal-pigmented epithelial cell line ARPE-19. RESULTS: Stimulation of ARPE-19 with live K. pneumoniae for 24h induced a 31.5-fold (p=0.0132) increase in IL-6 and 6.5-fold (p=0.0004) increase in MCP-1 levels compared to the non-infected control cells. Purified K. pneumoniae LPS (1µgml(-1)) also induced cytokine levels, MCP-1 (1.7-fold upregulation; p=0.0006) and IL-6 (1.3-fold upregulation, p=0.065). The tested K. pneumoniae strain ATCC 43816 did not have a significant effect on the viability of ARPE-19 cells (11% decrease, p=0.096) and showed a low ability to invade the cells. CONCLUSIONS: Both whole live K. pneumoniae and K. pneumoniae LPS exert a strong pro-inflammatory effect on retinal pigmented epithelial cells, consistent with clinical manifestations of disease. Bacterial pro-inflammatory effects are not likely related to host cell invasion. This is the first investigation of the interactions of a major endogenous endophthalmitis pathogen, K. pneumoniae with human retinal pigmented epithelial cells.

Both the unique and repeat regions of the Porphyromonas gingivalis hemagglutin A are involved in adhesion and invasion of host cells.

Porphyromonas gingivalis is one of the major etiologic agents of adult periodontitis and has been associated with cardiovascular diseases. It expresses multiple hemagglutinins that are significant virulence factors and play an important role in bacterial attachment and invasion of host cells. The objective of this study was to determine the impact of P. gingivalis hemagglutinin A (HagA) on the attachment to and invasion of human coronary artery endothelial cells (HCAEC) and gingival epithelial cells (GEC). Bacterial strains expressing the HagA protein (or subunits), including Escherichia coli carrying plasmid pEKS5, E. coli carrying plasmid ST2, and Salmonella enterica serovar Typhimurium with plasmid pNM1.1 were used in this study. The strains were tested for their ability to attach to and invade HCAEC and GEC using antibiotic protection assays. In addition, the unique 5' N-terminal non-repeated segment of HagA was purified in recombinant form and a monoclonal antibody was created against the polypeptide. The monoclonal antibody against the unique portion of HagA was tested for inhibitory activity in these assays. The attachment of both E. coli strains expressing HagA fragment to host cells was significantly increased compared to their respective controls. However, they did not invade GEC or HCAEC. Interestingly, HagA expression in the Salmonella strain increased both adherence to and invasion of HCAEC, which may be due to the presence of the entire hagA ORF. A monoclonal antibody against the unique 5' N-terminal portion of HagA reduced invasion. Further experiments are needed to determine the role of the unique and the repeat segments of P. gingivalis HagA.

Intracellular survival and vascular cell-to-cell transmission of Porphyromonas gingivalis.

BACKGROUND: Porphyromonas gingivalis is associated with periodontal disease and invades different cell types including epithelial, endothelial and smooth muscle cells. In addition to P. gingivalis DNA, we have previously identified live invasive bacteria in atheromatous tissue. However, the mechanism of persistence of this organism in vascular tissues remains unclear. Therefore, the objective of this study was to analyze the ability of intracellular P. gingivalis to persist for extended periods of time, transmit to and possibly replicate in different cell types. RESULTS: Using antibiotic protection assays, immunofluorescent and laser confocal microscopy, we found that after a prolonged intracellular phase, while P. gingivalis can still be detected by immunostaining, the intracellular organisms lose their ability to be recovered in vitro. Surprisingly however, intracellular P. gingivalis could be recovered in vitro upon co incubation with fresh vascular host cells. We then demonstrated that the organism was able to exit the initially infected host cells, then enter and multiply in new host cells. Further, we found that cell-to-cell contact increased the transmission rate but was not required for transmission. Finally, we found that the invasion of new host cells allowed P. gingivalis to increase its numbers. CONCLUSION: Our results suggest that the persistence of vascular tissue-embedded P. gingivalis is due to its ability to transmit among different cell types. This is the first communication demonstrating the intercellular transmission as a likely mechanism converting latent intracellular bacteria from state of dormancy to a viable state allowing for persistence of an inflammatory pathogen in vascular tissue.

Detection of bacterial DNA in atheromatous plaques by quantitative PCR.

This is the first study to analyze atheromatous plaques for the presence of bacterial DNA from ten species, including periodontal species and Chlamydia pneumoniae. We examined 129 samples of DNA extracted from atheromas from 29 individuals for the presence of bacterial 16S rDNA sequences from ten different species: Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans (A.a.), Tannerella forsythensis, Eikenella corrodens, Prevotella intermedia, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mutans, Treponema denticola and C. pneumoniae. All determinations were made using real-time quantitative polymerase chain reaction (PCR) methods employing SYBR Green. Species from the Bacteroides family were found in about 17% of the young but approximately 80% in elderly patients. Almost half of the samples contained DNA from A. a. and C. pneumoniae, although the proportion of the latter was minimal. S. aureus and S. epidermidis were found with the lowest frequency, 5 and 10%, respectively. S. mutans was found in approximately 20% of the samples. The proportions of each bacterial species were calculated relative to the total amount of prokaryotic DNA. The data support our previous findings of an association between periodontal organisms and vascular inflammation. We conclude that DNA from oral infectious agents is commonly found in atheromas from young but especially from elderly subjects, and that the contribution of C. pneumoniae to the inflammation may be minimal.

Infection-associated biomarkers of inflammation in atherosclerosis.

Atherosclerosis is a systemic inflammatory disease leading to lipid-laden inflammatory lesions in the arterial walls that may destabilize and rupture. It is becoming clear that addressing the "classical" risk factors for atherosclerosis does not entirely reduce the risk of cardiovascular events. Novel biomarkers to be used in highthroughput assays are necessary for diagnosis, for determination of the residual risk and for monitoring the effects of the therapy. Since inflammation is a hallmark of atherosclerosis, tests for pro-inflammatory biomarkers have been introduced such as for hsCRP, fibrinogen and IL-6, with many more at different stages of development. There has been a dearth of novel approaches for the diagnosis and management of atherosclerosis, reflected in a continuous reliance on LDL cholesterol as a proven target of investigations. To bring another perspective, here we briefly overview the accumulated epidemiological and sero-epidemiological evidence suggesting systemic infections as a component of atherosclerotic inflammations. We have shown that different individuals' plaques are colonized with different bacterial species (atherosclerosis microbiota). Most of the time the pathogens are likely in an intracellular state, shielded from the host immune responses. There are controlled clinical trials and metaanalyses that corroborate the infections, specifically periodontal disease as a contributing risk factor of atherosclerosis. Infection-related markers, including transcriptome signatures, may identify latent infection patients with sub-clinical disease. Thus, the emerging infection- associated markers of inflammation could complement the existing ones and their use as companion diagnostics for atherosclerosis should stimulate the growing field of personalized medicine within cardiovascular diseases.

Role of gut microbiota in the modulation of atherosclerosis-associated immune response.

Inflammation and metabolic abnormalities are linked to each other. At present, pathogenic inflammatory response was recognized as a major player in metabolic diseases. In humans, intestinal microflora could significantly influence the development of metabolic diseases including atherosclerosis. Commensal bacteria were shown to activate inflammatory pathways through altering lipid metabolism in adipocytes, macrophages, and vascular cells, inducing insulin resistance, and producing trimethylamine-N-oxide. However, gut microbiota could also play the atheroprotective role associated with anthocyanin metabolism and administration of probiotics and their components. Here, we review the mechanisms by which the gut microbiota may influence atherogenesis.

View of statins as antimicrobials in cardiovascular risk modification.

Atherosclerosis is a complex arterial pathological development underlying heart attack and stroke and a leading cause of death in developed and now also in developing countries. The primary processes that lead to the inflammatory lipid-laden proliferative lesion, obstructing the blood flow, and referred to as atherosclerotic plaque are dyslipidaemia and inflammation. Here, we will review one of the most efficient classes of drugs indicated for management of cardiovascular disease (CVD), statins. We will assess their pleiotropic effects that emerged from CVD applications, focusing this review specifically on plausible antimicrobial activity. Only recently gaining strength, the recognition of possible antibacterial activity may extend the statin applicability for vascular as well as to other critical inflammatory conditions.

Intestinal mucosal tolerance and impact of gut microbiota to mucosal tolerance.

The mucosal barriers are very sensitive to pathogenic infection, thereby assuming the capacity of the mucosal immune system to induce protective immunity to harmful antigens and tolerance against harmless substances. This review provides current information about mechanisms of induction of mucosal tolerance and about impact of gut microbiota to mucosal tolerance.

Periodontal bacterial invasion and infection: contribution to atherosclerotic pathology.

OBJECTIVE: The objective of this review was to perform a systematic evaluation of the literature reporting current scientific evidence for periodontal bacteria as contributors to atherosclerosis. METHODS: Literature from epidemiological, clinical and experimental studies concerning periodontal bacteria and atherosclerosis were reviewed. Gathered data were categorized into seven "proofs" of evidence that periodontal bacteria: 1) disseminate from the oral cavity and reach systemic vascular tissues; 2) can be found in the affected tissues; 3) live within the affected site; 4) invade affected cell types in vitro; 5) induce atherosclerosis in animal models of disease; 6) non-invasive mutants of periodontal bacteria cause significantly reduced pathology in vitro and in vivo; and 7) periodontal isolates from human atheromas can cause disease in animal models of infection. RESULTS: Substantial evidence for proofs 1 to 6 was found. However, proof 7 has not yet been fulfilled. CONCLUSIONS: Despite the lack of evidence that periodontal bacteria obtained from human atheromas can cause atherosclerosis in animal models of infection, attainment proofs 1 to 6 provides support that periodontal pathogens can contribute to atherosclerosis.

Bacterial invasion of vascular cell types: vascular infectology and atherogenesis.

To portray the chronic inflammation in atherosclerosis, leukocytic cell types involved in the immune response to invading pathogens are often the focus. However, atherogenesis is a complex pathological deterioration of the arterial walls, where vascular cell types are participants with regards to deterioration and disease. Since other recent reviews have detailed the role of both the innate and adaptive immune response in atherosclerosis, herein we will summarize the latest developments regarding the association of bacteria with vascular cell types: infections as a risk factor for atherosclerosis; bacterial invasion of vascular cell types; the atherogenic sequelae of bacterial presence such as endothelial activation and blood clotting; and the identification of the species that are able to colonize this niche. The evidence of a polybacterial infectious component of the atheromatous lesions opens the doors for exploration of the new field of vascular infectology and for the study of atherosclerosis microbiome.

Genomic comparison of invasive and rare non-invasive strains reveals Porphyromonas gingivalis genetic polymorphisms.

BACKGROUND: Porphyromonas gingivalis strains are shown to invade human cells in vitro with different invasion efficiencies, varying by up to three orders of magnitude. OBJECTIVE: We tested the hypothesis that invasion-associated interstrain genomic polymorphisms are present in P. gingivalis and that putative invasion-associated genes can contribute to P. gingivalis invasion. DESIGN: Using an invasive (W83) and the only available non-invasive P. gingivalis strain (AJW4) and whole genome microarrays followed by two separate software tools, we carried out comparative genomic hybridization (CGH) analysis. RESULTS: We identified 68 annotated and 51 hypothetical open reading frames (ORFs) that are polymorphic between these strains. Among these are surface proteins, lipoproteins, capsular polysaccharide biosynthesis enzymes, regulatory and immunoreactive proteins, integrases, and transposases often with abnormal GC content and clustered on the chromosome. Amplification of selected ORFs was used to validate the approach and the selection. Eleven clinical strains were investigated for the presence of selected ORFs. The putative invasion-associated ORFs were present in 10 of the isolates. The invasion ability of three isogenic mutants, carrying deletions in PG0185, PG0186, and PG0982 was tested. The PG0185 (ragA) and PG0186 (ragB) mutants had 5.1×10(3)-fold and 3.6×10(3)-fold decreased in vitro invasion ability, respectively. CONCLUSION: The annotation of divergent ORFs suggests deficiency in multiple genes as a basis for P. gingivalis non-invasive phenotype.

Cultivation of Enterobacter hormaechei from human atherosclerotic tissue.

AIM: To determine whether culturable bacterial strains are present in human atheromatous tissue and to investigate their properties using culture, quantitative PCR, metagenomic screening, genomic and biochemical methods. METHODS: We analyzed femoral atherosclerotic plaque and five pairs of diseased and healthy arterial tissue for the presence of culturable bacteria using cell cultures and genomic analysis. RESULTS: Gram negative aerobic bacilli were cultivated from the plaque tissue. Ribosomal 16S DNA amplification and sequencing identified the isolates as Enterobacter hormaechei. The isolate was resistant to ampicillin, cefazolin, and erythromycin. A circular 10 kb plasmid was isolated from the strain. Antibiotic protection assays of the isolate demonstrated invasive ability in a human monocytic cell line. To extend the study, five matched pairs of diseased and healthy aortic tissue were analyzed via quantitative PCR. Eubacterial 16S rDNA was detected in all specimens, however, E. hormaechei DNA was detected in surprisingly high numbers in two of the diseased tissues only. CONCLUSIONS: While it is well documented that inflammation is an important risk factor for vascular pathophysiology, the association of bacteria with atherosclerosis has not been clearly established, in large part due to the inability to isolate live bacteria from atheromatous tissue. This is the first study providing direct evidence of Enterobacter spp. associated with atheromatous tissues. The data suggest that chronic infection with bacteria may be an under-reported etiologic factor in vascular pathogenesis. Importantly, characterization of the clinical isolate supports a model of atherogenesis where systemic dissemination of bacteria to atherosclerotic sites may occur via internalization in phagocytic cells.

Hemagglutinin B is involved in the adherence of Porphyromonas gingivalis to human coronary artery endothelial cells.

Porphyromonas gingivalis is a periodontopathogen that may play a role in cardiovascular diseases. Hemagglutinins may function as adhesins and are required for virulence of several bacterial pathogens. The aim of this study was to determine the role of hemagglutinin B (HagB) in adherence of P. gingivalis to human coronary artery endothelial (HCAE) cells. P. gingivalis strain 381, a P. gingivalis 381 HagB mutant, Escherichia coli JM109 expressing HagB (E. coli-HagB), and E. coli JM109 containing pUC9 (E. coli-pUC9) were tested for their ability to attach to HCAE cells. Inhibition assays were performed to determine the ability of purified recombinant HagB (rHagB) as well as antibodies to HagB, including the polyclonal antibody (PAb) A7985 and the monoclonal antibody (MAb) HL1858, to inhibit the attachment of P. gingivalis to HCAE cells. As expected, when the attachment of P. gingivalis and the HagB mutant were compared, no statistical significance was observed between the two groups (P = 0.331), likely due to the expression of the hagB homolog hagC. However, E. coli-HagB adhered significantly better to HCAE cells than did E. coli-pUC9, the control strain. In a competition assay, the presence of purified rHagB decreased bacterial adhesion of P. gingivalis or E. coli-HagB to HCAE cells. The presence of PAb A7985 or MAb HL1858 also significantly decreased attachment of P. gingivalis and E. coli-HagB to host cells. These results indicate that HagB is involved in the adherence of P. gingivalis to human primary endothelial cells.

Genes of periodontopathogens expressed during human disease.

BACKGROUND: Since many bacterial genes are environmentally regulated, the screening for virulence-associated factors using classical genetic and molecular biology approaches can be biased under laboratory growth conditions of a given pathogen, because the required conditions for expression of many virulence factors may not occur during in vitro growth. Thus, technologies have been developed during the past several years to identify genes that are expressed during disease using animal models of human disease. However, animal models are not always truly representative of human disease, and with many pathogens, there is no appropriate animal model. METHODS: A new technology, in vivo-induced antigen technology (IVIAT) was thus engineered and tested in our laboratory to screen for genes of pathogenic organisms induced specifically in humans, without the use of animal or artificial models of infection. This technology uses pooled sera from patients to probe for genes expressed exclusively in vivo (or ivi, in vivo-induced genes). IVIAT was originally designed for the study of Actinobacillus actinomycetemcomitans pathogenesis, but we have now extended it to other oral pathogens including Porphyromonas gingivalis. RESULTS: One hundred seventy-one thousand (171,000) clones from P. gingivalis strain W83 were screened and 144 were confirmed positive. Over 300,000 A. actinomycetemcomitans clones were probed, and 116 were confirmed positive using a quantitative blot assay. CONCLUSION: MAT has proven useful in identifying previously unknown in vivo-induced genes that are likely involved in virulence and are thus excellent candidates for use in diagnostic : and therapeutic strategies, including vaccine design.