Effects of the antimicrobial peptide cathelicidin (LL-37) on immortalized gingival fibroblasts infected with Porphyromonas gingivalis and irradiated with 625-nm LED light.

Porphyromonas gingivalis causes chronic inflammatory diseases (periodontal diseases) that destroy the periodontal ligament and alveolar bone. Antimicrobial peptides are crucial components of the host defense response required to maintain cellular homeostasis during microbial invasion. Because light-emitting diode (LED) irradiation influences the host defense response against bacterial infections, we investigated its effect on immortalized gingival fibroblasts (IGFs) infected with P. gingivalis. IGFs were incubated with P. gingivalis following LED irradiation at 425, 525, and 625 nm. The dark 1 group comprised noninfected, nonirradiated IGFs, and the dark 2 group comprised nonirradiated IGFs infected with P. gingivalis. These groups served as controls. Infected cells and controls were assayed for reactive oxygen species (ROS) and were subjected to RT-PCR and Western blotting analyses to determine the levels of expression of antimicrobial peptides. LED irradiation enhanced the bactericidal effects of the antimicrobial peptide LL-37 in cells infected with P. gingivalis. Irradiation at 625 nm decreased inflammatory responses involving the release of prostaglandin E2 induced by ROS in P. gingivalis-infected IGFs. LED irradiation at 625 nm induces an anti-inflammatory response that elicits the production of antimicrobial peptides, providing an efficacious method of treatment for periodontal diseases.