Background: Periodontal disease is suggested to increase the risk of atherothrombotic disease by inducing dyslipidemia. Recently, we demonstrated that proprotein convertase subtilisin/kexin type 9 (PCSK9), which is known to play a critical role in the regulation of circulating low-density lipoprotein (LDL) cholesterol levels, is elevated in periodontitis patients. However, the underlying mechanisms of elevation of PCSK9 in periodontitis patients are largely unknown. Here, we explored whether Porphyromonas gingivalis, a representative periodontopathic bacterium, -induced inflammatory response regulates serum PCSK9 and cholesterol levels using animal models. Methods: We infected C57BL/6 mice intraperitoneally with Porphyromonas gingivalis, a representative strain of periodontopathic bacteria, and evaluated serum PCSK9 levels and the serum lipid profile. PCSK9 and LDL receptor (LDLR) gene and protein expression, as well as liver X receptors (Lxrs), inducible degrader of the LDLR (Idol), and sterol regulatory element binding transcription factor (Srebf)2 gene expression, were examined in the liver. Results: P. gingivalis infection induced a significant elevation of serum PCSK9 levels and a concomitant elevation of total and LDL cholesterol compared with sham-infected mice. The LDL cholesterol levels were significantly correlated with PCSK9 levels. Expression of the Pcsk9, Ldlr, and Srebf2 genes was upregulated in the livers of the P. gingivalis-infected mice compared with the sham-infected mice. Although Pcsk9 gene expression is known to be positively regulated by sterol regulatory element binding protein (SREBP)2 (human homologue of Srebf2), whereas Srebf2 is negatively regulated by cholesterol, the elevated expression of Srebf2 found in the infected mice is thought to be mediated by P. gingivalis infection. Conclusions: P. gingivalis infection upregulates PCSK9 production via upregulation of Srebf2, independent of cholesterol levels. Further studies are required to elucidate how infection regulates Srebf2 expression and subsequently influences lipid metabolism.

This study aimed to clarify the antibacterial and antibiofilm effects of ferulic acid against periodontal pathogenic bacteria. The cytotoxicity of ferulic acid was examined using the MTT assay on the human oral epithelial cell line Ca9-22. To determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration, Porphyromonas gingivalis ATCC 33277, Fusobacterium nucleatum ATCC 25586, Prevotella intermedia ATCC 25611, Aggregatibacter actinomycetemcomitans JP2, and Streptococcus mitis ATCC 903 were treated with ferulic acid. The inhibition of biofilm formation was evaluated by crystal violet staining. The inhibition of P. gingivalis autoinducer-2 (AI-2) production and receptor activity was evaluated by luminescence measurements using the sensor strain Vibrio harveyi BB170. Ferulic acid did not exhibit any cytotoxicity on human oral epithelial cells. The MICs of ferulic acid against P. gingivalis and A. actinomycetemcomitans were 1000 and 500 µg/mL, respectively. It did not show antibacterial activity against F. nucleatum, P. intermedia, and S. mitis, indicating the weak antibacterial activity of ferulic acid. However, ferulic acid significantly inhibited P. gingivalis biofilm formation at low concentrations below 1/8 MIC. It specifically inhibited AI-2 production from P. gingivalis below 1/8 MIC and suppressed the receptor activity of AI-2. Although ferulic acid showed weak antibacterial activity against periodontopathogenic bacteria, it had low cytotoxicity and inhibited P. gingivalis biofilm formation. Ferulic acid inhibited AI-2 production and receptor activity, suggesting that ferulic acid is an efficient quorum-sensing inhibitor for controlling P. gingivalis biofilm formation.