Neodymium-doped Yttrium-Aluminium-Garnet Laser Irradiation Abolishes the Increase in Interleukin-6 Levels Caused by Peptidoglycan through the p38 Mitogen-activated Protein Kinase Pathway in Human Pulp Cells

The anti-inflammatory effects of low-power laser irradiation have previously been reported. However, how the laser irradiation regulates the expression of inflammatory cytokines remains unknown. In the present study, to elucidate the mechanism behind the anti-inflammatory effect, we examined the effects of low-power neodymium-doped yttrium-aluminium-garnet (Nd:YAG) laser irradiation on interleukin (IL)-6 expression in human pulp (HP) cells stimulated by peptidoglycan (PGN) and focused on intracellular signaling pathways. Low-power Nd:YAG laser irradiation obviated the PGN-induced increase in IL-6 levels in HP cells. A p38 mitogen-activated protein kinase inhibitor, SB203580, also inhibited the increase in IL-6 messenger RNA levels. PGN stimulated the activity of phosphorylated p38 in HP cells. Low-power laser irradiation inhibited the activity. Thus, suppression of the phosphorylated p38 activity by low-power laser irradiation in HP cells culminates in inhibition of the increase in IL-6 induced by PGN, suggesting that low-power laser irradiation regulates intracellular signaling molecule activities to exert its anti-inflammatory effect.