Porphyromonas gingivalis infection accelerates the progression of atherosclerosis in a heterozygous apolipoprotein E-deficient murine model

Induction of monocyte chemoattractant protein-1 by Porphyromonas gingivalis in human endothelial cells

The association between periodontal and cardiovascular diseases could be mediated by direct interaction of periodontal pathogens with cardiac tissue. In order to explore this possibility, the effect of the periodontal pathogen Porphyromonas gingivalis on monocyte chemoattractant protein-1 (MCP-1) production by endothelial cells was investigated. When incubated with live P. gingivalis 381, MCP-1 production by human umbilical vein endothelial cells (HUVEC) was potently increased. Compared to the type strain 381, non-adhesive/invasive strains (W50 and DPG3) did not increase MCP-1 production, which was also demonstrated at the mRNA level. Killed P. gingivalis 381 was much less effective than live bacteria for MCP-1 induction. Treatment of HUVEC with cytochalasin D, an inhibitor of endocytosis, prevented MCP-1 mRNA up-regulation by P. gingivalis 381, suggesting that internalization of P. gingivalis is necessary for MCP-1 induction. In conclusion, the secretion of high levels of MCP-1 resulting from interactions of P. gingivalis with endothelial cells could enhance atherosclerosis progression by contributing to the recruitment of monocytes.

Cellular Responses to Oral Pathogens

BACKGROUND

Several previous epidemiological studies, along with the results of more recent animal model approaches, have suggested a role for periodontitis in atherosclerosis. Such an association could be mediated by direct interactions of periodontopathic bacteria with host vascular tissues.

METHODS

The interactions of Porphyromonas gingivalis with endothelial cells and macrophages in vitro were investigated relative to modification of low-density lipoproteins (LDL).

RESULTS

P. gingivalis 381, its outer membrane vesicles, and the lipopolysaccharide (LPS) derived from these organisms were all shown to induce modification of LDL in the presence of the murine macrophage J774.A.1. Such alterations led to an increase in the migration of the particles through agarose gels. In addition, direct modification of LDL by strain 381 was demonstrated in the absence of macrophages. This latter property appears to be related to the potent protease activities of the bacterium. These properties may contribute to modification of LDL to forms which have been strongly implicated in cholesterol lipid accumulation in vascular tissues. P. gingivalis 381 also appears to induce cyclooxygenase-2 expression in endothelial cells as determined with human umbilical vascular endothelial cells (HUVEC).

CONCLUSIONS

These in vitro results with vascular cells in culture suggest a molecular basis for a potential role for periodontopathic bacteria such as P. gingivalis in augmenting foam cell formation characteristic of atherosclerotic lesions.

CD14-mediated induction of interleukin-8 and monocyte chemoattractant protein-1 by a heat-resistant constituent of Porphyromonas gingivalis in endothelial cells

Viable and inactivated Porphyromonas gingivalis dose-dependently induced interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) secretion in human umbilical vein endothelial cells (HUVECs). The inactivated P. gingivalis, in comparison with viable bacteria, tended to enhance the production of both chemokines more strongly. The production of MCP-1 protein began increasing immediately after stimulation by P. gingivalis, and there was a nearly linear increase from 0 to 8 h of incubation, whereas IL-8 production showed a linear increase between 4 and 12 h of incubation. The IL-8 and MCP-1 mRNA expressions in HUVECs as determined by reverse transcriptase-polymerase chain reaction (RT-PCR) or Quantikine mRNA colorimetric quantification kits were found to be enhanced by P. gingivalis. Furthermore, the time courses of IL-8 and MCP-1 mRNA expressions were in accordance with those of protein production. Addition of polymyxin B or boiling did not weaken the stimulatory effect of P. gingivalis, which inhibited the effect of Escherichia coli lipopolysaccharide (E. coli LPS) and tumour necrosis factor-alpha (TNF-alpha), respectively. In contrast, the induction of IL-8 and MCP-1 by P. gingivalis was significantly reduced by anti-CD14 antibody. Our results suggest that some heat-stable component of P. gingivalis, including LPS, may be responsible for the induction of IL-8 and MCP-1 in HUVECs by a CD14-dependent mechanism. These effects might be involved in the accumulation and activation of neutrophils and monocytes at an early stage of the periodontal pathogenesis.

A role for glycoprotein Ib in Streptococcus sanguis-induced platelet aggregation

Numerous studies have implicated bacteria in cardiovascular disease, but there is a paucity of information on the mechanism involved. In this study we show how the common oral bacterium Streptococcus sanguis can directly interact with platelets, resulting in activation and aggregate formation. Platelet aggregation was dependent on glycoprotein IIb/IIIa (GPIIb/IIIa) and thromboxane. Platelets could also directly bind to S sanguis, but this interaction was not inhibited by GPIIb/IIIa antagonists. Antibodies to GPIb could inhibit both platelet aggregation and platelet adhesion to bacteria. This suggested a direct interaction between GPIb and S sanguis; however, this interaction did not require von Willebrand factor, the normal ligand for GPIb. By use of a range of monoclonal antibodies to GPIb and the enzyme mocharagin, which cleaves GPIb at amino acid 282, the interaction was localized to a region within the N-terminal 1-225 portion of GPIbalpha. Furthermore S sanguis failed to induce aggregation of platelets from a patient with Bernard-Soulier disease, the organism bound to Chinese hamster ovary cells transfected with the GPIbalpha gene but did not bind to mock-transfected cells and biotin-labeled S sanguis cells bound to purified GPIb in ligand blots. It is suggested that the interaction between S sanguis and GPIb is important in the pathogenesis of infective endocarditis and may also play a contributory role in some cases of myocardial infarction.

Infections and their role in atherosclerotic vascular disease

BACKGROUND

Complications of atherosclerosis are the leading cause of mortality in developed countries, and infections may play a role in the pathogenesis. Numerous studies have addressed this issue in the past decade.

TYPES OF STUDIES REVIEWED

The author examined peer-reviewed studies and reviews on the role of microbes or infections in atherosclerosis, cardiovascular disease and cerebrovascular disease. He included selected articles on epidemiology, pathology, in vitro experiments, animal models and clinical studies.

RESULTS

Cross-sectional and retrospective studies have shown an association between Chlamydia pneumoniae antibodies and cardiovascular disease, but prospective studies have not been as convincing. Studies on the association between cardiovascular disease and periodontal disease or loss of teeth have produced conflicting results. Cytomegalovirus infection is associated mainly with accelerated arteriosclerosis after cardiac transplantation. Infectious agents can induce biological mechanisms important for atherogenesis. Mice and rabbit studies have indicated that C. pneumoniae is capable of initiating or accelerating the progression of atherosclerosis. Limited studies on cytomegalovirus also suggest the ability to induce early changes of atherosclerosis in a rodent model. Preliminary clinical trials of treatment for C. pneumoniae infection suggest a possible short-term benefit, but larger randomized trials for longer periods are in progress.

CONCLUSION AND CLINICAL IMPLICATIONS

Infectious agents may play an important role in atherogenesis, but currently the jury is not in. Further management of cardiovascular disease could change radically if this concept were proven.