Effect of 635nm Light-Emitting Diode Irradiation on Intracellular Superoxide Anion Scavenging Independent of the Cellular Enzymatic Antioxidant System

Objective: The aim of this study was to examine the reactive oxygen species (ROS) that are dissipated by 635 nm irradiation, and the effect of 635 nm irradiation on ROS scavenging system. Background data: Intracellular ROS are produced in the form of superoxide anion by either nicotinamide adenine dinucleotide phosphate (NADPH) oxidase or xanthine oxidase in response to a number of stimuli. Low-level light irradiation decreases the intracellular ROS level and has been used in clinical situations for reducing the level of oxidative stress. Methods: Human epithelial cells were exposed to exogenous and endogenous oxidizing agents that promote the generation of harmful ROS. These were then irradiated with 635nm LED light, 5 mW/cm(2) for 1 h, 18 J/cm(2) or by 470nm LED light, also 5 mW/cm(2) for 1 h, 18 J/cm(2) on a 9 cm cell culture dish. After irradiation, the MTT reduction method and malondialdehyde (MDA) colorimetric assay were performed in xanthine/xanthine oxidase (XXO)- or hydrogen peroxide (H2O2)-treated HaCaT cells. The superoxide anion was detected by an electron spin resonance (ESR) spectrometer using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin trap and H2O2 was assayed by flow cytometry using 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA). Results: Irradiation at 635nm enhanced cell viability in the XXO-treated HaCaT cells. Also, irradiation had a much lesser effect on cell viability in the HaCaT cells treated with exogenous H2O2 as compared with that in cells treated with N-acetyl-L-cysteine. The level of the superoxide anion increased in response to XXO treatment, and then decreased after 635nm irradiation. Irradiation with 635nm led to a decrease in superoxide anion and lipid peroxidation levels in the presence or absence of diethyldithiocarbamate. Conclusions: These results highlight the potential role of 635nm irradiation in protection against oxidative stress by scavenging superoxide anions. Also, a pathway that is independent of the activities of intracellular enzymatic ROS scavengers, such as superoxide dismutase, glutathione peroxidase and catalase might be involved in its mechanism of action.