Toxic Effects of Visible-light Irradiation on Eugenol-treated Oral Mucosa

Methods: HGF cells were obtained in accordance with the guidelines of the local ethics committee. HGF cells and mouse oral mucous membranes were treated with two agents, EUG and IsoEUG, in the absence or presence of VL irradiation. The cells were irradiated with a dental VL lamp from a distance of 10 cm for various times. Twelve adult mice (ICR, 8 weeks) were used for this experiment. The oral mucosa was treated for 1 minute with a 1-cm-diameter round filter paper soaked in each reagent (about 0.5 ml) under anaesthesia, and then irradiated with VL for 0 or 5 minutes. H-E and TUNEL (ApopTag® kit) staining were performed.

Results: The concentrations of EUG and IsoEUG producing damage to 50% of the HGF cells were 0.23 mM and 0.03 mM, respectively. EUG-treated HGF cells were highly damaged by VL, whereas IsoEUG-treated cells were highly damaged even without VL. At the tissue level, VL irradiation caused severe inflammation of mucosa treated with EUG or IsoEUG in comparison with unirradiated mucosa, and the damage caused by IsoEUG treatment was greater than that caused by EUG treatment. Induction of apoptosis was determined using the TUNEL method, but the predominant change shown in VL-irradiated EUG- or IsoEUG-treated mucous membranes was necrosis.

Conclusions: IsoEUG caused markedly greater damage to tissue and HGF cells than EUG, and the toxic effects of both compounds were highly enhanced by VL irradiation.