New gum disease treatment kills harmful bacteria while saving beneficial microbes

Researchers at Nagoya University in Japan have created an innovative treatment for periodontitis that targets and eliminates harmful bacteria while preserving beneficial oral microbes essential for health. The findings were published in the Journal of Translational Medicine.

Oral health relies on a diverse and balanced microbial community. Porphyromonas gingivalis (P. gingivalis) is a keystone pathogen that triggers inflammation and disrupts this balance. Such disruption can damage the bone supporting teeth and eventually lead to tooth loss.

Current treatments for periodontitis, including antibiotics and antimicrobial photodynamic therapy (aPDT), eliminate both pathogenic and beneficial oral bacteria. These approaches often disrupt the entire oral microbial ecosystem and can also release lipopolysaccharide (LPS), an endotoxin that may exacerbate inflammation."

Kazuhide Sato, one of the corresponding authors and lecturer, Nagoya University

To address these challenges, researchers from Nagoya University Graduate School of Medicine, including first author Hiroshi Maruyama, Professor Hideharu Hibi, and corresponding authors Sato and Kiyoshi Sakai, adapted near-infrared photoimmunotherapy, a technique originally developed for cancer treatment. This method uses an antibody-dye compound that binds to target cells and is activated by near-infrared light.

Expanding on this therapy, the team developed a method using IgY, an antibody from egg yolks of hens immunized against P. gingivalis. Because IgY can be produced in large quantities at low cost, it offers significant clinical potential. The researchers evaluated this new approach, called near-infrared photo-antibacterial targeting therapy (NIR-PAT²), in human cell cultures and mice to eliminate P. gingivalis while preserving a healthy oral environment, comparing its performance to conventional therapies.

Selective elimination of pathogens without damaging healthy tissue

In cell culture experiments, the antibody-dye compound selectively bound to P. gingivalis, leaving other bacteria and healthy human gum cells unaffected. When exposed to near-infrared light, the dye accumulated on P. gingivalis, disrupted its outer membrane, and eliminated the bacterium.

Microscopic analysis showed that treated P. gingivalis developed small membrane holes but retained its overall structure, while aPDT resulted in complete bacterial destruction. Tests confirmed that the new therapy did not harm human gum cells, whereas aPDT caused cellular injury and delayed healing.

Reduction of bone loss and improved oral microbiota in mouse models

In mouse models of periodontitis, the new treatment significantly reduced alveolar bone loss. Saliva analysis indicated that the therapy improved oral microbiota by eliminating pathogenic P. gingivalis while preserving beneficial Streptococcus populations. In comparison, standard antibiotics and aPDT removed both pathogenic and beneficial bacteria, further disrupting the oral microbiota.

"Results demonstrated that, unlike antibiotics or standard light therapy, this approach selectively removes the primary pathogenic species while preserving the remainder of the oral bacterial community," Sato said.

To achieve clinical application

The researchers explain that periodontitis is caused by several types of bacteria, so focusing on just one may not be enough. They intend to use artificial intelligence (AI) to analyze publicly available oral bacteria data to identify other important species and better understand how they interact. These insights will help develop more precise treatments.

Because periodontitis is connected to health issues such as rheumatoid arthritis and diabetes, the researchers believe that their AI-driven analysis could also help determine which patients are most likely to benefit from targeted treatments.