Characterization of lethal action of near-ultraviolet on retinal pigment epithelial cells in vitro

Melanin Precursor 5,6-Dihydroxyindol: Protective Effects and Cytotoxicity on Retinal Cells in vitro and in vivo

5,6-Dihydroxyindole (DHI) is a melanin pigment precursor with antioxidant properties. In the light of a report about cytotoxicity of DHI, the aim of this study was to assess possible toxic effects of DHI on cells related to the eye, such as human ARPE-19 cells and mouse retinal explants. Moreover, DHI was tested on its effects on retinal function in vivo using electroretinography. We found cytotoxicity of DHI against ARPE-19 cells at 100 μM, but not at 10 μM. 10 μM DHI exhibited a slight, though not significant protective activity against UV-A damage in ARPE-19 cells. We found cytoprotection in cultured mouse retinas by 50 μM DHI or its diacetylated derivative 5,6-diacetoxyindole (DAI), respectively. In ERG measurements in vivo, amplitudes were decreased only slightly by 100 μM DHI compared to saline, whereas a better preservation of amplitudes was visible at 10 μM DHI, in particular with respect to cones. In histological sections, more cones were found at 10 μM DHI than at 100 μM DHI. As a conclusion, DHI shows a slight protective effect at 10 μM both in vitro and in vivo. At 100 μM, it shows a strong cytotoxicity in vitro, which is strongly reduced in vivo.

Artificial senescence of bovine retinal pigment epithelial cells induced by near-ultraviolet in vitro

RPE cells irradiated by near-ultraviolet (NUV) were characterized at cellular, biochemical and molecular levels in order to determine whether light-induced RPE changes contribute to the senescence of RPE cells in vitro. Biochemical and molecular parameters of cellular senescence were studied by using both bovine RPE cells at confluence repeatedly irradiated by NUV (peaking at 365 nm) and RPE cells at different levels of population doubling (PDL). After repeated NUV irradiation, RPE proliferation was markedly suppressed. In parallel, the BrdU index significantly reduced to a minimum level, similar to RPE cells undergoing multiple population doublings. NUV irradiation resulted in a decrease in cellular alkali-soluble melanin and an increase in lipofuscin-like fluorophores. The lipofuscin-like fluorophores, isolated from RPE cells exposing repeated NUV irradiation, represented a gradual hyperchromic change and red-shift, reaching the wavelength maxima (560-572 nm), at excitation wavelength of 365 nm, a typical range of 'age pigment'. These phenomena were substantially eliminated in oxygen-free conditions. Both the NUV-irradiated RPE cells and RPE cells at 20 Pd expressed 4 to 8-fold and 2 to 4-fold less PEDF and TIMP-3 genes, respectively. As result of experiments using chronic photochemical treatment, RPE cells represented several characteristics of cellular senescence. In addition to alterations of the melanin/lipofuscin system, DNA synthesis was greatly suppressed in NUV-irradiated RPE cells, indicating replicative senescence. The phenomena of downregulation of the possible senescence markers imply that photochemical reactions of RPE cells accelerate the process of RPE senescence.

Extracellular matrix of retinal pigment epithelium regulates choriocapillaris endothelial survival in vitro

The role of extracellular matrix of retinal pigment epithelial cells (RPE-ECM) in the regulation of the survival of choriocapillaris endothelial cells (CCE) was investigated in vitro. The CCE survival was evaluated by trypan blue staining, neutral red uptake, and the counting of viable cells. Results showed that CCE cells survived on RPE-ECM. Pre-treatment of RPE-ECM individually with neutralizing antibodies to acidic fibroblast growth factor, vascular endothelial growth factor, platelet-derived growth factor, or transforming growth factor beta(pan specific to TGFbeta1, TGFbeta1.2, TGFbeta2 and TGFbeta5), did not alter the survival rate of CCE cells on RPE-ECM, as compared to that of the control (CCE survival rates on RPE-ECM pretreated with normal rabbit IgG). However, the treatment of RPE-ECM with neutralizing antibody to basic fibroblast growth factor (bFGF) caused CCE death by 77.1+/-15.7%. The CCE death was defined as apoptosis based on the morphological markers (shrinkage in cell size with blebbing of plasma membranes, condensation and fragmentation of nuclei, and DNA fragmentation in multiples of approximately 200 bp). The addition of phorbol 12-myristate 13-acetate (PMA) (2 nM) to the culture medium was effective for complete prevention of CCE apoptosis; the protecting effect of PMA on CCE apoptosis can be abolished by H7 (25 microM), but not HA1004 (50 microM), suggesting the involvement of PKC in protecting CCE from apoptosis. The inhibition of protein synthesis of CCE cells by cycloheximide (0.1 microM) did not affect the apoptotic process of the cells. In a separate experiment, when CCE cells were cultured in a medium saturated with bFGF (5 ng ml-1) without RPE-ECM, the cells also died by apoptosis. However, this apoptotic process was not affected by PMA. Cycloheximide also failed to affect the apoptotic process. These results suggest that both RPE-ECM insoluble molecules and RPE-ECM-bound bFGF modulate choriocapillaris survival by suppressing CCE apoptosis.