Possibility of Involvement of Porphyromonas gingivalis in Coronary Heart Disease

Porphyromonas gingivalis has been implicated in periodontal diseases. Accumulating evidence suggests that cardiovascular disease is the most prevalent medical problem in patients with periodontal diseases. In order to check the possibility that P. gingivalis is involved in coronary heart disease, the present study was performed to observe P. gingivalis adherence and invasion of human coronary artery endothelial cells (HCAEC) and production of cytokines and growth factors by HCAEC upon P. gingivalis infection. $^3H$-labeled P. gingivalis 381 was incubated with HCAEC for 90 min. The radioactivity of the washed HCAEC was a measure of the absorbed (adhering and invading) P. gingivalis. The absorption radioactivity of the HCAEC infected by P. gingivalis was determined to be 59.58% of the input bacterial cells. In contrast, the absorption radioactivity of the cells infected by S. gordonii Challis which was employed as a control was negligible (0.59%). DPG3, a P. gingivalis mutant defective of fimbriae, appeared to be impaired to some extent in capability of adherence/invasion as compared to that of the parental strain 381, showing 43.04% of the absorption radioactivity. The absorption radioactivity of the HCAEC infected by P. gingivalis 381 in the presence of excessive fimbriae at the concentrations of $50\;{\mu}g$ and $100\;{\mu}g/ml$ was 57.27 and 45.44%, respectively. Invasion of HCAEC by P. gingivalis 381 was observed by an antibiotic (metronidazole) protection assay and transmission electron microscopy (TEM). In the antibiotic protection assay, invasion by the bacterium was measured to be 0.73, 1.09, and 1.51% of the input bacterial cells after incubation for 30, 60, and 90 min, respectively. Invasion by DPG3 was shown to be 0.16% after 90-min incubation. In comparison of invasion efficiency at 90 min of the incubation, the invasion efficiency of DPG3 was 0.37% while that of its parental strain 381 was 2.54%. The immunoblot analysis revealed fimbriae of P. gingivalis did not interact with the surface of HCAEC. These results suggest that fimbriae are not the major contribution to the adherence of P. gingivalis to HCAEC but may be important in the invasion of HCAEC by the bacterium. The presence of cytochalasin D ($1\;{\mu}g/ml$) and staurosporine ($1\;{\mu}M$) reduced the invasion of HCAEC by P. gingivalis 381 by 78.86 and 53.76%, respectively, indicating that cytoskeletal rearrangement and protein kinase of HCAEC are essential for the invasion. Infection of P. gingivalis induced HCAEC to increase the production of TNF-${\alpha}$. by 60.6%. At 90 min of the incubation, the HCAEC infected with P. gingivalis cells was apparently atypical in the shape, showing loss of the nuclear membrane and subcellular organelles. The overall results suggest that P. gingivalis may cause coronary heart disease by adhering to and invading endothelial cells, and subsequently damaging the cells.