The effect of low-level laser irradiation on the proliferation, osteogenesis, inflammatory reaction, and oxidative stress of human periodontal ligament stem cells under inflammatory conditions

Abstract

Periodontitis often causes damage to the periodontal tissue and affects the function of human periodontal ligament stem cells (hPDLSCs). Low-level laser therapy (LLLT) has been used for periodontal treatment and can upregulate the proliferation and osteogenesis of hPDLSCs. The purpose of this study was to investigate the effects of LLLT on the proliferation, osteogenic differentiation, inflammatory reaction, and oxidative stress of hPDLSCs in an inflammatory environment (pPDLSCs). We designed one control group and three testing groups (treated with Nd:YAG laser at 4, 8, and 16 J/cm²) of hPDLSCs from periodontitis patients who were diagnosed with stable phase periodontitis. Cell proliferation was measured by colony-forming unit fibroblast (CFU-F) assays and 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assays. The osteogenic capacity of the cells was determined by alkaline phosphatase (ALP) staining, ALP activity assays, Alizarin Red S staining and the mRNA transcript levels of runt-related transcription factor 2 (Runx2), ALP, and osteocalcin (OCN). The effects of LLLT on the secretion of tumor necrosis factor-α (TNF-α) and interleukin (IL)-1β by PDLSCs were measured by enzyme-linked immunosorbent assay (ELISA). We also evaluated the oxidative stress of hPDLSCs and pPDLSCs by measuring the reactive oxygen species (ROS) level, malondialdehyde (MDA) level, and superoxide dismutase (SOD) activity after treatment with LLLT at 4, 8, and 16 J/cm². Our results demonstrated that LLLT could modulate the osteogenic potential of pPDLSCs at 8 J/cm². Inflammatory stimuli induced excess ROS release, and LLLT at 4-8 J/cm² promoted oxidative stress levels in hPDLSCs but decreased the expression of inflammatory cytokines and ROS levels in pPDLSCs. Moreover, LLLT at 16 J/cm² could significantly suppress proliferation and osteogenic differentiation and promote inflammatory cytokines and ROS levels in pPDLSCs. In conclusion, LLLT could regulate proliferation, osteogenesis, inflammatory reaction, and oxidative stress of human periodontal ligament stem cells under inflammatory conditions.

Keywords: Human periodontal ligament stem cells; Inflammation; Low-level laser therapy; Osteogenesis; Proliferation; Reactive oxygen species.