Blue light-induced apoptosis in cultured retinal pigment epithelium cells of the rat.
BACKGROUND
We previously demonstrated that phagosome-free retinal pigment epithelium (RPE) cells in culture can be damaged directly by blue light (wavelength 440+/-10 nm) as observed by electron microscope. A low intensity (1.0 mW/cm2) of light induced only swelling of mitochondria, while a high intensity (4.0 mW/cm2) induced necrosis in the RPE. The aim of the present study was to investigate what intensity of blue light could induce apoptosis in cultured phagosome-free RPE.


METHODS
Primary cultured RPE cells, harvested from Long-Evans rats, that contained no phagosomes were exposed to a cool blue light (wavelength 440+/-10 nm). After exposure, transmission electron microscopy (TEM) and TdT-mediated dUTP nick-end labeling (TUNEL) staining were used to detect apoptosis in the RPE cells. To assess the relationship of oxidation to apoptosis by blue light, we added N-acetylcysteine (NAC) as a free radical scavenger and investigated its inhibitory effect on apoptosis.


RESULTS
In RPE cells exposed to blue light of 2.7 mW/cm2 for 24 h, apoptotic bodies were found by TEM. In RPE cells exposed to blue light of 2.0 mW/cm2 for 60 h, apoptotic bodies, nuclear condensation and nuclear segmentation were observed by TEM and some RPE cells showed positive TUNEL staining. When 30 mM of NAC was added, TUNEL staining was negative.


CONCLUSIONS
Our findings demonstrate that apoptotic cell death is induced by blue light exposure in cultured RPE cells in vitro. The findings of our previous experiments and those of the present study suggest that a higher intensity of blue light could induce necrosis, and moderately intense blue light could induce non-necrotic cell death or apoptosis, in RPE cells. Furthermore, it is suggested that blue light caused cell death by a free-radical-associated mechanism.
Seko
Y
Y
Department of Ophthalmology and Visual Science, Tokyo Medical and Dental University Graduate School, Japan.
Pang
J
J
Tokoro
T
T
Ichinose
S
S
Mochizuki
M
M
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects*; D002478:Cells, Cultured; D016166:Free Radical Scavengers / Q000494:pharmacology; D020287:In Situ Nick-End Labeling; D008027:Light / Q000009:adverse effects*; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000528:radiation effects* / Q000648:ultrastructure; D051381:Rats; D020318:Rats, Long-Evans
D016166:Free Radical Scavengers; D000111:Acetylcysteine