Oral P. gingivalis infection alters the vascular reactivity in healthy and spontaneously atherosclerotic mice

Porphyromonas gingivalis regulates atherosclerosis through an immune pathway

Atherosclerosis (AS) is a chronic inflammatory disease, involving a pathological process of endothelial dysfunction, lipid deposition, plaque rupture, and arterial occlusion, and is one of the leading causes of death in the world population. The progression of AS is closely associated with several inflammatory diseases, among which periodontitis has been shown to increase the risk of AS. Porphyromonas gingivalis (P. gingivalis), presenting in large numbers in subgingival plaque biofilms, is the “dominant flora” in periodontitis, and its multiple virulence factors are important in stimulating host immunity. Therefore, it is significant to elucidate the potential mechanism and association between P. gingivalis and AS to prevent and treat AS. By summarizing the existing studies, we found that P. gingivalis promotes the progression of AS through multiple immune pathways. P. gingivalis can escape host immune clearance and, in various forms, circulate with blood and lymph and colonize arterial vessel walls, directly inducing local inflammation in blood vessels. It also induces the production of systemic inflammatory mediators and autoimmune antibodies, disrupts the serum lipid profile, and thus promotes the progression of AS. In this paper, we summarize the recent evidence (including clinical studies and animal studies) on the correlation between P. gingivalis and AS, and describe the specific immune mechanisms by which P. gingivalis promotes AS progression from three aspects (immune escape, blood circulation, and lymphatic circulation), providing new insights into the prevention and treatment of AS by suppressing periodontal pathogenic bacteria.

The impact of periodontitis on vascular endothelial dysfunction

Periodontitis, an oral inflammatory disease, originates from periodontal microbiota dysbiosis which is associated with the dysregulation of host immunoinflammatory response. This chronic infection is not only harmful to oral health but is also a risk factor for the onset and progress of various vascular diseases, such as hypertension, atherosclerosis, and coronary arterial disease. Vascular endothelial dysfunction is the initial key pathological feature of vascular diseases. Clarifying the association between periodontitis and vascular endothelial dysfunction is undoubtedly a key breakthrough for understanding the potential relationship between periodontitis and vascular diseases. However, there is currently a lack of an updated review of their relationship. Therefore, we aim to focus on the implications of periodontitis in vascular endothelial dysfunction in this review.

Oral Microbiota: A Major Player in the Diagnosis of Systemic Diseases

The oral cavity is host to a complex and diverse microbiota community which plays an important role in health and disease. Major oral infections, i.e., caries and periodontal diseases, are both responsible for and induced by oral microbiota dysbiosis. This dysbiosis is known to have an impact on other chronic systemic diseases, whether triggering or aggravating them, making the oral microbiota a novel target in diagnosing, following, and treating systemic diseases. In this review, we summarize the major roles that oral microbiota can play in systemic disease development and aggravation and also how novel tools can help investigate this complex ecosystem. Finally, we describe new therapeutic approaches based on oral bacterial recolonization or host modulation therapies. Collaboration in diagnosis and treatment between oral specialists and general health specialists is of key importance in bridging oral and systemic health and disease and improving patients' wellbeing.

Periodontitis induces endothelial dysfunction in mice

The treatment of periodontitis has numerous positive effects on established chronic health conditions, including cardiovascular disease and diabetes. However, ethical considerations do limit the establishment of human trials to investigate whether periodontitis promotes the early stages of chronic conditions. Therefore, the aim of this study was to investigate whether periodontitis induces endothelial dysfunction in hyperlipidemic apolipoprotein E gene-deficient (ApoE^-/-) mice. Forty-five 8-week-old ApoE^-/- mice were challenged by oral lavage with Porphyromonas gingivalis and Streptococcus gordonii for 4 weeks. A subgroup of animals (n = 15-17/group) was placed in a metabolic chamber immediately before euthanasia at 4 weeks to measure VO₂/CO₂ concentrations and voluntary locomotion. In infected and control animals alveolar bone levels were measured by x-ray imaging and endothelial function was determined by measuring endothelial-dependent vasorelaxation of aortic rings. The mRNA expression levels of serum amyloid A and tumor necrosis factor were determined in liver tissues by qRT PCR and protein concentrations in serum by ELISA. Caecal contents were analysed by sequencing to determine changes to the gut microbiota to investigate linkages between microbiome and systemic changes. The results showed that oral lavage of P. gingivalis and S. gordonii for 4 weeks, initiated periodontitis in ApoE^-/- mice, similar to the human situation. The oral inflammation was accompanied by a significant increase in mRNA expression of pro-inflammatory mediators serum amyloid A1 and tumor necrosis factor in the liver. Mice with periodontitis also exhibited impaired endothelial-dependent vasorelaxation responses to acetylcholine. This systemic response was connected to increased energy expenditure, locomotion and respiratory quotient. No differences were detected in caecal microbiota between the infected and control animals. Overall, this is the first report that provide evidence that periodontitis induces endothelial dysfunction in mice. Other systemic responses observed in response to the local reaction need further investigation. The study suggests that early prevention of periodontitis may help limit the early stages of endothelial dysfunction that is linked to atherogenesis in humans.

Mechanisms underlying the association between periodontitis and atherosclerotic disease

Atherosclerosis is central to the pathology of cardiovascular diseases, a group of diseases in which arteries become occluded with atheromas that may rupture, leading to different cardiovascular events, such as myocardial infarction or ischemic stroke. There is a large body of epidemiologic and animal model evidence associating periodontitis with atherosclerotic disease, and many potential mechanisms linking these diseases have been elucidated. This chapter will update knowledge on these mechanisms, which generally fall into 2 categories: microbial invasion and infection of atheromas; and inflammatory and immunologic. With respect to the invasion and infection of atheromas, it is well established that organisms from the subgingival biofilm can enter the circulation and lodge in most distant tissues. Bacteremias resulting from oral interventions, and even oral hygiene activities, are well documented. More recently, indirect routes of entry of oral organisms (via phagocytes or dendritic cells) have been described for many oral organisms, into many tissues. Such organisms include the periodontal pathogens Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Prevotella intermedia, Tannerella forsythia, and Fusobacterium nucleatum. Intracellular survival of these organisms with dissemination to distant sites (The Trojan Horse approach) has been described. Their relative contribution to atheroma formation and progression has been studied mainly in experimental research, with results demonstrating that these organisms can invade endothelial cells and phagocytic cells within the atheroma, leading to pathogenic changes and progression of the atheroma lesion. The second category of mechanisms potentially linking periodontitis to atherosclerosis includes the dumping of inflammatory mediators originating from periodontal lesions into the systemic circulation. These inflammatory mediators, such as C-reactive protein, matrix metalloproteinases, fibrinogen, and other hemostatic factors, would further accelerate atheroma formation and progression, mainly through oxidative stress and inflammatory dysfunction. Moreover, direct effects on lipid oxidation have also been described. In summary, the evidence supports the concept that periodontitis enhances the levels of systemic mediators of inflammation that are risk factors for atherosclerotic diseases.

The Distinct Immune-Stimulatory Capacities of Porphyromonas gingivalis Strains 381 and ATCC 33277 Are Determined by the fimB Allele and Gingipain Activity

The Porphyromonas gingivalis strain ATCC 33277 (33277) and 381 genomes are nearly identical. However, strain 33277 displays a significantly diminished capacity to stimulate host cell Toll-like receptor 2 (TLR2)-dependent signaling and interleukin-1β (IL-1β) production relative to 381, suggesting that there are strain-specific differences in one or more bacterial immune-modulatory factors. Genomic sequencing identified a single nucleotide polymorphism in the 33277 fimB allele (A→T), creating a premature stop codon in the 33277 fimB open reading frame relative to the 381 fimB allele. Gene exchange experiments established that the 33277 fimB allele reduces the immune-stimulatory capacity of this strain. Transcriptome comparisons revealed that multiple genes related to carboxy-terminal domain (CTD) family proteins, including the gingipains, were upregulated in 33277 relative to 381. A gingipain substrate degradation assay demonstrated that cell surface gingipain activity is higher in 33277, and an isogenic mutant strain deficient for the gingipains exhibited an increased ability to induce TLR2 signaling and IL-1β production. Furthermore, 33277 and 381 mutant strains lacking CTD cell surface proteins were more immune-stimulatory than the parental wild-type strains, consistent with an immune-suppressive role for the gingipains. Our data show that the combination of an intact fimB allele and limited cell surface gingipain activity in P. gingivalis 381 renders this strain more immune-stimulatory. Conversely, a defective fimB allele and high-level cell surface gingipain activity reduce the capacity of P. gingivalis 33277 to stimulate host cell innate immune responses. In summary, genomic and transcriptomic comparisons identified key virulence characteristics that confer divergent host cell innate immune responses to these highly related P. gingivalis strains.

Apolipoprotein E, periodontal disease and the risk for atherosclerosis: a review

The association between cardiovascular and periodontal diseases is characterized by chronic inflammatory processes, with a high prevalence worldwide and complex genetic-environment interactions. Although apolipoprotein E4 (ApoE4), one of the isoforms coded by a polymorphic APOE gene, has been widely recognized as a risk factor for cardiovascular diseases and as an immunoinflammatory factor, less is known regarding how ApoE4 affects atherosclerosis in periodontitis patients. The aim of this review was to investigate the potential underlying mechanisms related to APOE4 that could increase the risk of periodontal disease and, ultimately, of atherosclerosis. There have only been a few studies addressing apoE polymorphisms in patients with chronic periodontitis. To date, no studies have been performed that have assessed how ApoE4 affects atherosclerotic disease in chronic periodontitis patients. Although clinical studies are warranted, experimental studies have consistently documented the presence of periodontal pathogens, which are usually found in the oral cavity and saliva, in the atherosclerotic plaques of ApoE-deficient mice. In addition, in this review, the potential role of the APOE4 allele as an example of antagonistic pleiotropy during human evolution and its relation to oral health is discussed.

Hypercholesterolemia-Induced Loss of Flow-Induced Vasodilation and Lesion Formation in Apolipoprotein E-Deficient Mice Critically Depend on Inwardly Rectifying K+ Channels

BACKGROUND

Hypercholesterolemia-induced decreased availability of nitric oxide (NO) is a major factor in cardiovascular disease. We previously established that cholesterol suppresses endothelial inwardly rectifying K+ (Kir) channels and that Kir2.1 is an upstream mediator of flow-induced NO production. Therefore, we tested the hypothesis that suppression of Kir2.1 is responsible for hypercholesterolemia-induced inhibition of flow-induced NO production and flow-induced vasodilation (FIV). We also tested the role of Kir2.1 in the development of atherosclerotic lesions.

METHODS AND RESULTS

Kir2.1 currents are significantly suppressed in microvascular endothelial cells exposed to acetylated-low-density lipoprotein or isolated from apolipoprotein E-deficient (Apoe-/- ) mice and rescued by cholesterol depletion. Genetic deficiency of Kir2.1 on the background of hypercholesterolemic Apoe-/- mice, Kir2.1+/-/Apoe-/- exhibit the same blunted FIV and flow-induced NO response as Apoe-/- or Kir2.1+/- alone, but while FIV in Apoe-/- mice can be rescued by cholesterol depletion, in Kir2.1+/-/Apoe-/- mice cholesterol depletion has no effect on FIV. Endothelial-specific overexpression of Kir2.1 in arteries from Apoe-/- and Kir2.1+/-/Apoe-/- mice results in full rescue of FIV and NO production in Apoe-/- mice with and without the addition of a high-fat diet. Conversely, endothelial-specific expression of dominant-negative Kir2.1 results in the opposite effect. Kir2.1+/-/Apoe-/- mice also show increased lesion formation, particularly in the atheroresistant area of descending aorta.

CONCLUSIONS

We conclude that hypercholesterolemia-induced reduction in FIV is largely attributable to cholesterol suppression of Kir2.1 function via the loss of flow-induced NO production, whereas the stages downstream of flow-induced Kir2.1 activation appear to be mostly intact. Kir2.1 channels also have an atheroprotective role.

Porphyromonas gingivalis in periodontal pockets and heart valves

BACKGROUND

There is evidence that advanced infectious chronic periodontal inflammatory disease may have an impact on general health including cardiovascular diseases. The aim of this clinical study was to evaluate the ability of Porphyromonas gingivalis to colonize heart valves and, subsequently, to assess whether there is an association between the presence of the DNA of Porphyromonas gingivalis in periodontal pockets and in degenerated heart valves.

MATERIALS AND METHODS

Thirty patients were enrolled in the study and 31 valve specimens harvested during cardiac surgery operations were examined. All patients underwent a periodontal examination. To evaluate the periodontal status of the patients the following clinical parameters were recorded: the pocket depth, bleeding on probing (BOP) and aproximal plaque index (API). The presence of P. gingivalis in heart valve specimens and samples from periodontal pockets was analyzed using a single-step PCR method.

RESULTS

P. gingivalis DNA was detected in periodontal pockets of 15 patients (50%). However, the DNA of this periopathogen was found neither in the aortic nor in the mitral valve specimens.

CONCLUSIONS

This study suggests that P. gingivalis may not have an influence on the development of the degeneration of aortic and mitral valves.

Porphyromonas gingivalis strain specific interactions with human coronary artery endothelial cells: a comparative study

Both epidemiologic and experimental findings suggest that infection with Porphyromonas gingivalis exacerbates progression of atherosclerosis. As P. gingivalis exhibits significant strain variation, it is reasonable that different strains possess different capabilities and/or mechanisms by which they promote atherosclerosis. Using P. gingivalis strains that have been previously evaluated in the ApoE null atherosclerosis model, we assessed the ability of W83, A7436, 381, and 33277 to adhere, invade, and persist in human coronary artery endothelial (HCAE) cells. W83 and 381 displayed an equivalent ability to adhere to HCAE cells, which was significantly greater than both A7436 and 33277 (P<0.01). W83, 381, and 33277 were more invasive than A7436 (P<0.0001). However, only W83 and A7436 were able to remain viable up to 48 hours in HCAE cell cultures, whereas 381 was cleared by 48 hours and 33277 was cleared by 24 hours. These differences in persistence were in part due to strain specific differences in intracellular trafficking. Both W83 and 381 trafficked through the autophagic pathway, but not A7436 or 33277. Internalized 381 was the only strain that was dependent upon the autophagic pathway for its survival. Finally, we assessed the efficacy of these strains to activate HCAE cells as defined by production of IL-6, IL-8, IL-12p40, MCP-1, RANTES, TNF-α, and soluble adhesion molecules (sICAM-1, sVCAM-1, and sE-selectin). Only moderate inflammation was observed in cells infected with either W83 or A7436, whereas cells infected with 381 exhibited the most profound inflammation, followed by cells infected with 33277. These results demonstrate that virulence mechanisms among different P. gingivalis strains are varied and that pathogenic mechanisms identified for one strain are not necessarily applicable to other strains.

Endothelial dysfunction in the apolipoprotein E-deficient mouse: insights into the influence of diet, gender and aging

Since the early 1990s, several strains of genetically modified mice have been developed as models for experimental atherosclerosis. Among the available models, the apolipoprotein E-deficient (apoE⁻/⁻) mouse is of particular relevance because of its propensity to spontaneously develop hypercholesterolemia and atherosclerotic lesions that are similar to those found in humans, even when the mice are fed a chow diet. The main purpose of this review is to highlight the key achievements that have contributed to elucidating the mechanisms pertaining to vascular dysfunction in the apoE⁻/⁻ mouse. First, we summarize lipoproteins and atherosclerosis phenotypes in the apoE⁻/⁻ mouse, and then we briefly discuss controversial evidence relative to the influence of gender on the development of atherosclerosis in this murine model. Second, we discuss the main mechanisms underlying the endothelial dysfunction of conducting vessels and resistance vessels and examine how this vascular defect can be influenced by diet, aging and gender in the apoE⁻/⁻ mouse.