Blue Light Induces Mitochondrial DNA Damage and Free Radical Production in Epithelial Cells

Abstract

Exposure of biological chromophores to ultraviolet radiation can lead to photochemical damage. However, the role of visible light, particularly in the blue region of the spectrum, has been largely ignored. To test the hypothesis that blue light is toxic to non-pigmented epithelial cells, confluent cultures of human primary retinal epithelial cells were exposed to visible light (390 -550 nm at 2.8 milliwatts/cm 2 ) for up to 6 h. A small loss of mitochondrial respiratory activity was observed at 6 h compared with dark-maintained cells, and this loss became greater with increasing time. To investigate the mechanism of cell loss, the damage to mitochondrial and nuclear genes was assessed using the quantitative PCR. Light exposure significantly damaged mitochondrial DNA at 3 h (0.7 lesion/10 kb DNA) compared with darkmaintained controls. However, by 6 h of light exposure, the number of lesions was decreased in the surviving cells, indicating DNA repair. Isolated mitochondria exposed to light generated singlet oxygen, superoxide anion, and the hydroxyl radical. Antioxidants confirmed the superoxide anion to be the primary species responsible for the mitochondrial DNA lesions. The effect of lipofuscin, a photoinducible intracellular generator of reactive oxygen intermediates, was investigated for comparison. Exposure of lipofuscin-containing cells to visible light caused an increase in both mitochondrial and nuclear DNA lesions compared with non-pigmented cells. We conclude that visible light can cause cell dysfunction through the action of reactive oxygen species on DNA and that this may contribute to cellular aging, age-related pathologies, and tumorigenesis.

Mechanisms involved in A2E oxidation

“…Support for the involvement of singlet oxygen in A2E photooxidation is further provided by the observation that azide, histidine and DABCO, all of which are quenchers/scavengers of singlet oxygen, suppress irradiation-induced death of cells that have accumulated A2E in culture; conversely, the effect is potentiated in deuterium oxide-based medium . Additionally, however, investigations employing a cholesterol peroxidation assay or electron paramagnetic resonance (EPR), suggest that aerobic irradiation of A2E or whole lipofuscin, with short-wavelength visible light, brings about the generation of reactive oxygen species other than singlet oxygen including superoxide anion (O 2•− ) and perhaps hydroxyl radical (•OH) Godley et al, 2005;Kanofsky et al, 2003;Pawlak et al, 2003;Rozanowska et al, 1995). An important question that we address here, is the extent to which superoxide anion can add to carbon-carbon double bonds of A2E to form oxidized A2E species.…”

Low-concentration mechanical biosensor based on a photonic crystal nanowire array

“…Second, the wavelength of our driving light can be broadband, ranging from ultraviolet to near infrared. In biosensing, this broad-band excitation capability enables the protection of the biomolecules that are sensitive to high-energy photons 23 , by using low-energy photon excitation, such as near infrared range.…”

The Protective Effects of a Dietary Carotenoid, Astaxanthin, Against Light-Induced Retinal Damage

“…Tomohiro Otsuka 1 , Masamitsu Shimazawa 1 , Tomohiro Nakanishi 1 exposed to light (6,7). It is known that ROS is produced by light exposure in the retina, and it evokes photoreceptor degeneration (8,9); thus, antioxidants such as dimethylthiourea (10), phenyl-N-tert-butyl nitrone (11), and 2,2,6,6-tetramethyl-4-piperidinol-1-oxyl (12) have been reported to be effective in animal experiments.…”