Blue light stress in retinal neuronal (R28) cells is dependent on wavelength range and irradiance.

The aim of our study was to elucidate the role of wavelength and irradiance in blue light retinal damage. We investigated the impact of blue light emitted from light-emitting diode (LED) modules with peaks at either 411nm (half bandwidth 17nm) or 470nm (half bandwidth 25nm) at defined irradiances of 0.6, 1.5 and 4.5W/m(2) for 411nm and 4.5W/m(2) for 470nm on retinal neuronal (R28) cells in vitro. We observed a reduction in metabolic activity and transmembrane potential of mitochondria when cells were irradiated at 411nm at higher irradiances. Furthermore, production of mitochondrial superoxide radicals increased significantly when cells were irradiated with 411nm light at 4.5W/m(2) . In addition, such irradiation caused an activation of the antioxidative glutathion system. Using vital staining, flow cytometry and western blotting, we were able to show that apoptosis only took place when cells were exposed to 411nm blue light at higher irradiances; necrosis was not observed. Enhanced caspase-3 cleavage product levels confirmed that this effect was dependent on light irradiance. Significant alterations of the above-mentioned parameters were not observed when cells were irradiated with 471nm light despite a high irradiance of 4.5W/m(2) , indicating that the cytotoxic effect of blue light is highly dependent on wavelength. The observed phenomena in R28 cells at 411nm (4.5W/m(2) ) point to an apoptosis pathway elicited by direct mitochondrial damage and increased oxidative stress. Thus, light of 411nm should act via impairment of mitochondrial function by compromising the metabolic situation of these retinal neuronal cells.