[The correlation between the concentrations of VEGF and PEDF and Ca2+-PKC signaling pathways in human retinal pigment epithelial cells cultured in vitro after exposuring to blue light]

OBJECTIVE

To investigate the concentrations of vascular endothelial growth factor (VEGF), pigment epithelium-derived factor (PEDF), inositol triphosphate (IP3) and diacylglycerol (DAG) in human retinal pigment epithelium (RPE) cells after exposuring to blue light, and to explore the relationship with Ca2+-PKC signaling pathways, to evaluate the role of Ca2+-PKC signaling pathways of blue-light irradiation induced apoptosis in RPE cells.

METHODS

The fourth generation human RPE cells in vitro were exposured to blue light (2000±500 lux) for 6 hours, 24 hours prolongation of post-exposure culture. The concentrations of VEGF, PEDF, IP3 and DAG were assayed by enzyme linked immunosorbent assay (ELISA). Cells were randomly divided into 6 groups, group A (control), group B (exposure to blue light), group C (exposure to blue light+PMA), group D (exposure to blue light+Calphostin C), group E (exposure to blue light+Nifedipine), group F (exposure to blue light+Calphostin C+Nifedipine). Flow cytometry was used to detect the apoptosis rate of human RPE cells in A, B and F group.

RESULTS

Comparing with group A (584.38±10.66), the concentration of VEGF in group B (700.70±5.88), group C (698.21±6.66) and group E (648.30±4.91) was higher, the difference was statistically significant (P=0.002, 0.002, 0.016). Comparing with group B (700.70±5.88), the concentration of VEGF in Group D (623.87±3.12) and E (648.30±4.91) was lower (P=0.001, 0.002). Comparing with group A (75.96±1.70), the concentration of PEDF in Group B (71.82±1.67) and C (72.43±0.58) was lower (P=0.004, 0.011), but the concentration of PEDF in Group D (86.31±1.35) and E (93.72±1.24) was higher (P=0.000, 0.000). Comparing with group B (71.82±1.67), the concentration of PEDF in Group D (86.31±1.35) and E (93.72±1.24) was higher (P=0.000, 0.000). Comparing with group A (7.70±0.29), the ratio of VEGF to PEDF in Group B (9.85±0.34) and Croup C (9.64±0.02) was higher (P=0.008, 0.027) Comparing with group B, The ratio of VEGF to PEDF in Group D (7.23±0.08) and E (6.92±0.06) was lower (P=0.016, 0.015). Comparing with group A (108.42±0.75, 995.47± 13.61), the concentration of IP3 and DAG in Group B (117.24±1.06, 1070.10±10.07), C (137.12±2.71, 1046.40±7.90), D (139.17±1.40, 1041.13±9.76) and E (149.61±0.77, 1273.14±10.89) was higher, the difference was statistically significant (P=0.003, 0.007, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000). Comparing with group B, the concentration of IP3 in Group C, D and E was higher (P=0.011, 0.000, 0.000). Comparing with group B, the concentration of DAG in Group C and D was lower (P=0.021, 0.007). Comparing with group B, the concentration of DAG in Group E was higher (P=0.000). Comparing with group A (10.27±1.88), the apoptosis rate of RPE cells in Group B(25.07±2.66) and F(19.37±3.23) was higher, the difference was statistically significant (P=0.001, 0.009). Comparing with group B (25.07±2.66), the apoptosis rate of RPE cells in Group F (19.37±3.23) was lower (P=0.038).

CONCLUSIONS

(1) After exposuring to blue light, the concentrations of VEGF, IP3 and DAG are increased and the ratio of VEGF to PEDF is also increased and the concentration of PEDF is decreased in human RPE cells. (2) L-Type Calcium Channels and Ca2+-PKC signaling pathways may be regulate the concentrations of VEGF, PEDF, IP3 and DAG in RPE cells after exposuring to blue light by feedback regulation. (3) The application of Calphostin C combined with Nifedipine may be restrain the apoptosis of RPE cells after exposuring to blue light.

High lenticular tolerance to ultraviolet radiation-B by pigmented guinea-pig; application of a safety limit strategy for UVR-induced cataract

PURPOSE

The purpose of this study was to determine a threshold measure, maximum tolerable dose (MTD), for avoidance of UVR-B-induced cataract in the pigmented guinea-pig.

METHODS

Thirty pupil-dilated anesthetized young female guinea-pigs, divided into five equal groups, received between 0 and 84.9 kJ/m(2) unilateral UVR-B. Lens extraction and in vitro lens photography occurred 24 hr after exposure. Measurement of intensity of lens light scattering served as quantifying tool for the degree of cataract. Data analysis included regression, using a second order polynomial model. The applied MTD concept was based on the UVR-B dose-response curve obtained for the pigmented guinea-pig. A smaller number of pigmented guinea-pigs, pigmented rats and albino rats underwent morphometric analysis of the anterior segment geometry.

RESULTS

All eyes exposed to UVR-B developed cataract in the anterior subcapsular region. MTD for avoidance of UVR-B-induced cataract was 69.0 kJ/m(2) in the pigmented guinea-pig. Iris was considerably thicker in the guinea-pig than in the rats. Lens blockage by the dilated iris was lowest in the guinea-pig.

CONCLUSIONS

Maximum tolerable dose for avoidance of UVR-B-induced cataract in the pigmented guinea-pig was 69.0 kJ/m(2), over 10-fold higher than the threshold 5 kJ/m(2) obtained by Pitts et al. in the pigmented rabbit. Maximum tolerable dose is an appropriate method for estimation of toxicity for UVR-B-induced cataract in the guinea-pig. The pigmented guinea-pig is significantly less sensitive to UVR-B exposure than the pigmented rabbit and pigmented rat.

Expression of Ubiquitin Carboxy-Terminal Hydrolase-L1 in Photocoagulated Human Retinal Pigment Epithelial Cells

PURPOSE

To date, the exact mechanisms involved in laser-induced remission of ocular neovascular disorders are still poorly understood. Recent studies suggest that the expression of various antiangiogenic cytokines is upregulated after thermal photocoagulation. In the current study, we sought to identify novel laser-regulated proteins in cultured human retinal pigment epithelial (HRPE) cells.

METHODS

Protein extracts from photocoagulated HRPE cells were subjected to 2D-gel electrophoresis. Potentially regulated protein spots were identified by mass spectroscopy. Regulation of protein and mRNA was determined by Western blot analysis and reverse transcription-polymerase chain reaction, respectively.

RESULTS

2D-Gel electrophoresis of HRPE whole-cell extracts exposed to photocoagulation revealed a reproducible increase in a protein band identified as ubiquitin carboxy-terminal hydrolase-L1 (UCH-L1) compared with untreated controls. Protein levels showed a time-dependent upregulation over 24 hr. UCH-L1 mRNA was maximally increased after 8 hr.

CONCLUSIONS

Our findings indicate that the ubiquitin-proteasome system contributes to the effects seen clinically after thermal photocoagulation in eyes with neovascular diseases of the retina or choroid. Because ubiquitin carboxy-terminal hydrolase-L1 has been shown to be involved in the regulation of cell cycle proteins, it may be speculated that deubiquitinating enzymes have a role in the regeneration and proliferation of retinal pigment epithelial cells.

Toxicity of Indocyanine Green (ICG) in Combination with Light on Retinal Pigment Epithelial Cells and Neurosensory Retinal Cells

PURPOSE

To evaluate the toxicity of indocyanine green (ICG) in combination with light.

METHODS

Human retinal pigment epithelial cells (ARPE-19) and rat neurosensory retinal cells (R28) were treated with four different concentrations of ICG in combination with light exposure. Cell viability, mitochondrial function, and DNA synthesis were measured.

RESULTS

All concentrations of ICG with 10 min of light exposure caused a significant decrease in mitochondrial dehydrogenase activity in R28 and ARPE-19 cells. ICG without light exposure did not decrease mitochondrial dehydrogenase activity. In both cell lines, [(3)H]thymidine incorporation was increased when treated with ICG with or without light. R28 cells did not show any significant decrease in cell viability.

CONCLUSIONS

The duration of light was a significant factor in ICG toxicity. ICG needs to be used with caution as it decreases the mitochondrial dehydrogenase activity and increases the DNA synthesis in retinal cells, markers for cell toxicity and dysfunction.

[Specification of reflectometric measurement complex to evaluate optic density of macular pigments and concentration of phototoxic chemicals in retina]

Suggestion is to specify reflectometric measurement complex based on digital multisensor imaginery fundus-camera, in order to evaluate optic density of macular pigments and concentration of phototoxic chemicals in human retina. The authors presented a review of role played by macular pigments (zeaxanthine and lutein) in human eye viability, analyzed yellow spot as a protective light filter against harmful effects of short-wave light, increasing optic image quality in human eye and responsible for colour vision. Role of evaluating the individual density of macular pigments was stressed as a forecasting efficient criterion of occupational selection in operators performing visual tasks of detection, distance and dimensions measurement for remote objects, monitoring the changeable circumstances.

Selective targeting of pigmented retinal pigment epithelial (RPE) cells by a single pulsed laser irradiation: an in vitro study

This work describes the selective targeting of pigmented retinal pigment epithelial (RPE) cells by a single pulsed laser irradiation. We observed: (1) single pulsed laser irradiation caused cellular damages on pigmented, and not on non-pigmented RPE cells at laser radiant exposure up to 2550 mJ/cm(2); (2) in the mixture of pigmented and non-pigmented RPE cells, single pulsed laser-induced damage was confined to pigmented RPE cells. This study demonstrates that the pigmented RPE cells can be selectively damaged, using a single pulsed laser irradiation, without thermal coagulation to adjacent non-pigmented RPE cells.

AcrySof Natural filter decreases blue light-induced apoptosis in human retinal pigment epithelium

PURPOSE

The effect of AcrySof filter (UV light-filtering chromophore; Alcon) and AcrySof Natural filter (UV- and blue light-filtering chromophores) on blue light-induced apoptosis in human retinal pigment epithelial (RPE) cells was evaluated.

DESIGN

Laboratory investigation

CLINICAL RELEVANCE

Acrysof Natural filter reduces the blue-light toxicity in RPE cells and may have a positive impact on age-related macular degeneration (AMD).

METHODS

RPE cells were exposed to blue light (430-450 nm) in the presence of either the AcrySof (UV only) filter or Acrysof Natural (UV and blue light) filter for 10 days. The rate of apoptosis was analyzed.

RESULTS

Blue light induced significant apoptosis in RPE cells. AcrySof Natural filter significantly reduced the blue light-induced apoptosis when compared to AcrySof filter. The amount of blue-light energy reaching the cells with the AcrySof filter was 4.25 mW/cm(2) and with the AcrySof Natural filter was 2.5 mW/cm(2).

CONCLUSIONS

AcrySof Natural filter significantly reduced blue light-induced apoptosis. This was most likely due to its filtering effect on blue wavelength light, which reduces the energy that reaches the cells. In patients with cataract who are at a high risk for AMD, the implantation of a blue light-filtering intraocular lens may be considered.

[The research of the protection of recombinant human erythropoietin in human RPE cells by light-induced injuries]

OBJECTIVE

The aim of this study was to assess the protection of recombinant human erythropoietin (rhEPO) in light-induced injures in human retinal pigment epithelial (RPE) cells.

METHODS

It was a experimental study. Cultured human RPE cells were exposed to light of 8w 2000 +/- 500 Lux for 12 hours. The 3-(4,5-dimethylthiazole-2y1)-2,5-diphenyl tetrazolium bromide (MTT) cell viability assay were used to assess the effects of rhEPO in light-induced injury on human RPE cells. The effect of inhibiting apoptosis of rhEPO was detected by AnnexinV-fluorescein isothiocyanate/Propidium iodium labeling and flow cytometry. The enzyme linked immunosorbant assay (ELISA) and immunocytochemical staining were used to assess the expressions of caspase-3 treated by different doses of rhEPO in light-induced injury on human RPE cells and examine the protective mechanism of rhEPO by treatment with AG490 (the special inhibitor of jak2).

RESULTS

There was a significant increase of inhibiting apoptosis in every rhEPO group, and cell viability was the highest in 40 U/ml rhEPO group, the value was 4.93 +/- 1.45/ml. The decrease in expression of caspase-3 was the most obvious in 40 U/ml rhEPO group, in which the value was 0.125 +/- 0.029 ng/ml. There was a significant increased effect on inhibiting apoptosis in every rhEPO group, and it was the most conspicuous in 40 U/ml rhEPO group. But these increased cell viability and effect on inhibiting apoptosis in rhEPO group were restrained by AG490, in which the value of apoptosis was 11.29 +/- 2.11/ml and the density of caspase-3 increased to 0.362 +/- 0.042 ng/ml.

CONCLUSIONS

It is suggested that rhEPO can protect human RPE cells from the light-induced injures. Its protective mechanism is principally mediated by the EPO-EPOR pathway, which subsequently leads to jak2 activation.

Photobleaching of melanosomes from retinal pigment epithelium: II. Effects on the response of living cells to photic stress

Melanosomes of the retinal pigment epithelium (RPE) are long lived organelles that may undergo photobleaching with aging, which can diminish the antioxidant efficiency of melanin. Here, isolated porcine RPE melanosomes were experimentally photobleached with visible light to simulate aging and compared with untreated granules or control particles (black latex beads) for their effects on the survival of photically stressed ARPE-19 cultures. Particles were delivered to cultures for uptake by phagocytosis then cells were exposed to violet light and analyzed by a new live cell imaging method to identify the time of apoptotic blebbing as a dynamic measure of reduced cell survival. Results indicated that untreated melanosomes did not decrease photic injury to ARPE-19 cells when compared with cells lacking particles or with cells containing control particles, as might be expected if melanin performed an antioxidant function. Instead cells with untreated melanosomes showed reduced survival indicated by an earlier onset of blebbing and a lower fraction of surviving cells after photic stress. Cell survival was reduced even further in stressed cells containing melanosomes that were photobleached, and survival decreased with increasing photobleaching time. Photobleaching of RPE melanosomes therefore makes cells containing them more sensitive to light-induced cytotoxicity. This observation raises the possibility that aged melanosomes increase RPE cell photic stress in situ, perhaps contributing to reduced tissue function and to degeneration of the adjacent retina that the RPE supports. How melanosomes (photobleached or not) interact with their local subcellular environment to modify RPE cell survival is poorly understood and is likely determined by the physicochemical state of the granule and its constituent melanin. The live cell imaging method introduced here, which permitted detection of a graded effect of photobleaching, provides a sensitive bioassay for probing the effects of melanosome modifications.

Photochemistry and photocytotoxicity of alkaloids from Goldenseal (Hydrastis canadensis L.) 3: effect on human lens and retinal pigment epithelial cells

The dried root or rhizome of Goldenseal (Hydrastis canadensis L.) contains several alkaloids including berberine, hydrastine, palmatine and lesser amounts of canadine and hydrastinine. Preparations derived from Goldenseal have been used to treat skin and eye ailments. Berberine, the major alkaloid in Goldenseal root powder, has been used in eye drops to treat trachoma, a disease characterized by keratoconjunctivitis. Berberine and palmatine are also present in extracts from Berberis amurensis Ruprecht (Berberidaceae) which are used to treat ocular disorders. We have previously shown that Goldenseal alkaloids are phototoxic to keratinocytes (Chem Res Toxicol. 14, 1529, 2001; ibid 19, 739, 2006) and now report their effect on human lens and retinal pigment epithelial cells. Human lens epithelial cells (HLE-B3) were severely damaged when incubated with berberine (25 microM) and exposed to UVA (5 J cm(-2)). Under the same conditions, palmatine was less phototoxic and hydrastine, canadine and hydrastinine were inactive. Moderate protection against berberine phototoxicity was afforded by the antioxidants ascorbate (2 mM) and N-acetylcysteine (5 mM). When exposed to UVA (5 J cm(-2)) both berberine (10 microM) and palmatine (10 microM) caused mild DNA damage as determined by the alkaline comet assay which measures single strand breaks. Berberine and palmatine are the only Goldenseal alkaloids with appreciable absorption above 400 nm. Because light at wavelengths below 400 nm is cut off by the anterior portion of the adult human eye only berberine and palmatine were tested for phototoxicity to human retinal pigment epithelial (hRPE) cells. Although berberine did damage hRPE cells when irradiated with visible light (lambda > 400 nm) approximately 10 times higher concentrations were required to produce the same amount of damage as seen in lens cells. Palmatine was not phototoxic to hRPE cells. Neither berberine nor palmatine photodamaged DNA in hRPE. Infusions of Goldenseal are estimated to contain approximately 1 mM berberine, while in tinctures the alkaloid concentration may be more than 10 times higher. Our findings show that eyewashes and lotions derived from Goldenseal or containing berberine must be used with caution when the eyes are exposed to bright sunlight but that oral preparations are not likely to cause ocular phototoxicity.

Optical detection of intracellular cavitation during selective laser targeting of the retinal pigment epithelium: dependence of cell death mechanism on pulse duration

Selective laser targeting of the retinal pigment epithelium (RPE) is an attractive method for treating RPE-associated disorders. We are developing a method for optically detecting intracellular microcavitation that can potentially serve as an immediate feedback of the treatment outcome. Thermal denaturation or intracellular cavitation can kill RPE cells during selective targeting. We examined the cell damage mechanism for laser pulse durations from 1 to 40 micros ex vivo. Intracellular cavitation was detected as a transient increase in the backscattered treatment beam. Cavitation and cell death were correlated for individual cells after single-pulse irradiation. The threshold radiant exposures for cell death (ED(50,d)) and cavitation (ED(50,c)) increased with pulse duration and were approximately equal for pulses of up to 10 micros. For 20 micros, the ED(50,d) was about 10% lower than the ED(50,c); the difference increased with 40-micros pulses. Cells were killed predominantly by cavitation (up to 10-micros pulses); probability of thermally induced cell death without cavitation gradually increases with pulse duration. Threshold measurements are discussed by modeling the temperature distribution around laser-heated melanosomes and the scattering function from the resulting cavitation. Detection of intracellular cavitation is a highly sensitive method that can potentially provide real-time assessment of RPE damage during selective laser targeting.

Phototoxicity in human retinal pigment epithelial cells promoted by hypericin, a component of St. John's wort

St. John's wort (SJW), an over-the-counter antidepressant, contains hypericin, which absorbs light in the UV and visible ranges. In vivo studies have determined that hypericin is phototoxic to skin and our previous in vitro studies with lens tissues have determined that it is potentially phototoxic to the human lens. To determine if hypericin might also be phototoxic to the human retina, we exposed human retinal pigment epithelial (hRPE) cells to 10(-7) to 10(-5) M hypericin. Fluorescence emission detected from the cells (lambda(ex) = 488 nm; lambda(em) = 505 nm) confirmed hypericin uptake by human RPE. Neither hypericin exposure alone nor visible light exposure alone reduced cell viability. However when irradiated with 0.7 J cm(-2) of visible light (lambda > 400 nm) there was loss of cell viability as measured by MTS and lactate dehydrogenase assays. The presence of hypericin in irradiated hRPE cells significantly changed the redox equilibrium of glutathione and a decrease in the activity of glutathione reductase. Increased lipid peroxidation as measured by the thiobarbituric acid reactive substances assay correlated to hypericin concentration in hRPE cells and visible light radiation. Thus, ingested SJW is potentially phototoxic to the retina and could contribute to retinal or early macular degeneration.

In vitro assays for evaluating the ultraviolet B-induced damage in cultured human retinal pigment epithelial cells

The present study demonstrates broadband UV-B-induced damage of cultured human retinal pigment epithelial cells as an effort to develop an in vitro model that can be used, along with in vivo research and other in vitro efforts, to evaluate the need for retinal UV protection in humans after cataract removal. The human retinal pigment epithelial cell line, ARPE-19, was cultured in two groups: control and treated. Treated cells were irradiated with three broadband UVB radiations at energy levels of 0.05, 0.1 and 0.2J/cm(2). After irradiation, cells were incubated for 48h while cellular viability, morphology, and phagocytotic activity were analyzed using the Alamar blue assay, confocal microscopy, and fluorescent microspheres. Confocal analysis concentrated on the study of the cell nuclei and mitochondria. The Alamar blue assay of UV-B-exposed cells showed dose and time-dependent decreases in cellular viability in comparison to control cells. Loss of cell viability was measured at the two higher energy levels (0.2 and 0.1J/cm(2)), but the cell group exposed to 0.05J/cm(2) showed no significant viability change at 1-h time point. Morphological evaluation also showed dose and time-dependent degradation of mitochondria and nucleic acids. Cells exposed with 0.05J/cm(2) UVB did not show significant degradation of mitochondria and nucleic acids during the entire culture period. Phagocytotic activity assay data for UVB-exposed cells showed dose-dependent decreases in phagocytotic activity in comparison with the control cells. The control cells have significantly greater capacities for uptake than the 0.1 and 0.2J/cm(2) UV-B-exposed cells, while the 0.05J/cm(2) UV-B-exposed cell group showed no significant difference from the control cell group. The findings suggest that UVB radiation-induced cultured RPE cell damage can be evaluated by assays that probe cellular viability, morphological change, and phagocytotic activity, and that these assay methods together provide a valuable in vitro model for ultraviolet radiation-induced retinal toxicology research.

Blue light irradiation inhibits the production of HGF by human retinal pigment epithelium cells in vitro

Blue visible light damage to retinal pigment epithelial cells occurs through a photooxidative mechanism and the resultant damage is hypothesized to induce or exacerbate age-related macular degeneration. The purpose of the present study was to identify changes in the cell growth and the expression of hepatocyte growth factor (HGF) in cultured human retinal pigment epithelium (RPE) cells as a result of both blue and red light irradiation. HGF is a growth factor and neurotrophic factor that stimulates growth of various ocular cells and promotes the survival of RPE and retinal neurons. Early passages of human RPE cells were exposed to blue light (460 nm) and red light (640 nm). Nonirradiated cells were used as controls. After 24 and 48 h, conditioned medium was collected and the amount of HGF was measured by ELISA. Cells were detached from the well and counted. Cell viability was evaluated by trypan-blue exclusion study. Blue light at dosage of 63 J/cm(2) significantly inhibited the growth of RPE cells without affecting of cell viability. Amounts of HGF in the culture medium were significantly inhibited by blue-light irradiation at the dosage from 32 to 63 J/cm(2). Red light at a dose of 174 J/cm(2) causes a nonsignificant inhibition of growth of RPE cells and a slight decrease of secretion of HGF. As HGF promotes survival of RPE cells and retinal neurons, the inhibition of production of HGF by visible light, especially by blue light, may enhance the phototoxic effects of visible light on the RPE and retinal neurons.

Modulation of Ku70/80, Clusterin/ApoJ Isoforms and Bax Expression in Indocyanine-Green-Mediated Photo-Oxidative Cell Damage

PURPOSE

In order to characterize the biological effects and molecular mechanism underlying indocyanine-green (ICG)-mediated photo-oxidative cell damage, human cultured retinal pigmented epithelium (RPE) cells preloaded with ICG were exposed to 810-nm laser irradiation. Cell viability and death induction were examined, as well as the modulation of proteins involved in cell death and DNA repair.

METHODS

ARPE-19 cells preloaded with 100 microM ICG were irradiated using continuous and micropulsed 810-nm laser for the dye photoactivation, and cell viability and apoptosis were evaluated. The expression and subcellular localization of Bax, Ku70, Ku80 and clusterin/ApoJ were analyzed by immunocytochemistry and Western blot.

RESULTS

ICG photoactivation induced apoptosis in RPE cells. The micropulsed laser irradiation induced a higher percentage of cell killing as compared to continuous wave. Cell killing was inhibited by sodium azide, suggesting the involvement of reactive oxygen species in the laser-induced cell damage. Bax was strongly induced after 4 and up to 24 h of treatment. The nuclear proapoptotic isoform of clusterin/ApoJ was selectively upregulated after 24 h of treatment. The DNA repair machinery was upregulated after 4 and up to 24 h.

CONCLUSION

These data elucidate some molecular mechanisms involved in cell death induced by ICG photosensitization. The increase and relocalization of Bax into the mitochondria and the upregulation and translocation of the proapoptotic isoform of clusterin/ApoJ in the nucleus demonstrated the involvement of these proteins in the photo-oxidative cell death pathway. These data point out new molecular targets and suggest potential applications in the therapy of the retinal diseases that could benefit by selective RPE treatment.

Damage thresholds for cultured retinal pigment epithelial cells exposed to lasers at 532 nm and 458 nm

The determination of safe exposure levels for lasers has come from damage assessment experiments in live animals, which typically involve correlating visually identifiable damage with laser dosimetry. Studying basic mechanisms of laser damage in animal retinal systems often requires tissue sampling (animal sacrifice), making justification and animal availability problematic. We determined laser damage thresholds in cultured monolayers of a human retinal pigment epithelial (RPE) cell line. By varying exposure duration and laser wavelength, we identified conditions leading to damage by presumed photochemical or thermal mechanisms. A comparison with literature values for ocular damage thresholds validates the in vitro model. The in vitro system described will facilitate molecular and cellular approaches for understanding laser-tissue interaction.

Age-dependent photoionization thresholds of melanosomes and lipofuscin isolated from human retinal pigment epithelium cells

Melanosomes and lipofuscin were isolated from 14-, 59-, and 76-year-old, human retinal pigment epithelium specimens and examined. The morphological features of these samples were studied by scanning electron microscopy and atomic force microscopy, and the photoionization properties were examined by photoelectron emission microscopy. Ovoid- and rod-shaped melanosomes were observed. The size of the granules and the distribution between the two shapes show no significant age-dependent change. However, there is a higher occurrence of irregularly shaped aggregates of small round granules in older samples which suggests degradation or damage to melanosomes occurs with age. The melanosomes from the 14-year-old donor eye are well characterized by a single photoionization threshold, 4.1 eV, while the two older melanosomes exhibit two thresholds around 4.4 and 3.6 eV. Lipofuscin from both young and old cells show two thresholds, 4.4 and 3.4 eV. The similarity of the potentials observed for aged melanosomes and lipofuscin suggest that the lower threshold in the melanosome sample reflects lipofuscin deposited the surface of the melanosome. The amount, however, is not sufficient to alter the density of the melanosome, and therefore these granules do not separate in a sucrose gradient at densities characteristic of the typical melanolipofuscin granule. These data suggest that thin deposits of lipofuscin on the surface of retinal pigment epithelium melanosomes are common in the aged eye and that this renders the melanosomes more pro-oxidant.

Influence of laser parameters on selective retinal treatment using single-phase heat transfer analyses

Selective thermal treatment to retina is induced by short pulsed lasers to denaturize retinal pigment epithelium (RPE) selectively, while sparing the sensitive photoreceptors. The problem associated with the usage of short pulsed laser is the difficulty in determining the correct dosimetry parameters. This study quantifies the influence of laser parameters over the therapeutic range. The laser-tissue interaction is numerically investigated by analyzing the transient temperature in ocular tissues during the treatment. The rate process analysis for thermal injury is employed to estimate the selective damage of retina. The contours of Arrhenius integral value (Omeg/ Omegamax) presented in this study show both the area and magnitude of damage caused by various laser parameters. Results reveal that the 2 micros pulsed laser with green wavelength and Gaussian profile is relatively more effective for selective retinal treatment. The repetition frequency of 100 Hz is found to produce selectively RPE damage, while higher frequencies produce collateral damage to neural retina and choroid located within 2 microm from the RPE interface.

Photobleaching of Melanosomes from Retinal Pigment Epithelium: I. Effects on Protein Oxidation

Melanin in the long-lived melanosomes of the retinal pigment epithelium (RPE) may undergo photobleaching with aging, which appears to diminish the antioxidant function of melanin and could make photobleached melanosomes less efficient in protecting biomolecules from oxidative modification. Here we analyzed whether photobleaching of melanosomes affects their ability to modify the oxidation state of nearby protein. As conventional methods developed to study soluble antioxidants are not well suited for analysis of granules such as melanosomes, we developed a new analytic method to focus on particle surfaces that involves experimentally coating granules with the cytoskeletal protein beta-actin to serve as a reporter for local protein oxidation. Isolated porcine RPE melanosomes were photobleached with visible light to simulate aging, then photobleached melanosomes, untreated melanosomes and control particles (black latex beads) were actin coated and illuminated in a photosensitized cell free system. Protein was re-stripped from particles and analyzed for carbonylation by Western blotting. Quantitative densitometry showed no reproducible differences for protein associated with untreated melanosomes when compared with control particles. Melanin has both anti- and pro-oxidant functions when light irradiated, but neither of these functions predominated in the protein oxidation assay when untreated melanosomes were used. However, protein extracted from photobleached melanosomes showed markedly increased carbonylation, both of associated actin and of endogenous melanosomal protein(s), and the effect increased with extent of granule photobleaching. Photobleaching of RPE melanosomes therefore changes the oxidation state of protein endogenous to the organelle and reduces the ability of the granule to modify the oxidation of exogenous protein near the particle surface. The results support the growing body of evidence that photobleaching of RPE melanosomes, which is believed to occur with aging, changes the physicochemical properties of the organelle and reduces the likelihood that the granules perform an antioxidant function.

Mitochondrial "movement" and lens optics following oxidative stress from UV-B irradiation: cultured bovine lenses and human retinal pigment epithelial cells (ARPE-19) as examples

Mitochondria provide energy generated by oxidative phosphorylation and at the same time play a central role in apoptosis and aging. As a byproduct of respiration, the electron transport chain is known to be the major intracellular site for the generation of reactive oxygen species (ROS). Exposure to solar and occupational ultraviolet (UV) radiation, and thus production of ROS and subsequent cell death, has been implicated in a large spectrum of skin and ocular pathologies, including cataract. Retinal pigment epithelial cell apoptosis generates photoreceptor dysfunction and ultimately visual impairment. The purpose of this article was to characterize in vitro changes following oxidative stress with UV-B radiation in (a) ocular lens optics and cellular function in terms of mitochondrial dynamics of bovine lens epithelium and superficial cortical fiber cells and (b) human retinal pigment epithelial (ARPE-19) cells. Cultured bovine lenses and confluent cultures of ARPE-19 cells were irradiated with broadband UV-B radiation at energy levels of 0.5 and 1.0 J/cm(2). Lens optical function (spherical aberration) was monitored daily up to 14 days using an automated laser scanning system that was developed at the University of Waterloo. This system consists of a single collimated scanning helium-neon laser source that projects a thin (0.05 mm) laser beam onto a plain mirror mounted at 45 degrees on a carriage assembly. This mirror reflects the laser beam directly up through the scanner table surface and through the lens under examination. A digital camera captures the actual position and slope of the laser beam at each step. When all steps have been made, the captured data for each step position is used to calculate the back vertex distance for each position and the difference in that measurement between beams. To investigate mitochondrial movement, the mitochondria-specific fluorescent dye Rhodamine 123 was used. Time series were acquired with a Zeiss 510 (configuration Meta 18) confocal laser scanning microscope equipped with an inverted Axiovert 200 M microscope and 40-x water-immersion C-Apochromat objective (NA 1.2). The optical analysis showed energy level-dependent increases in back vertex distance variability (loss of sharp focus) from 0.39 +/- 0.04 mm (control, n = 11) to 1.63 +/- 0.33 mm (1.0 J/cm(2), n = 10) and 0.63 +/- 0.13 mm (0.5 J/cm(2), n = 9). Confocal laser scanning microscopy analysis of both bovine lenses and ARPE-19 cells showed that following treatment at 0.5 J/cm(2) the mitochondria stopped moving immediately whereas at 1.0 J/cm(2) not only did the mitochondria stop moving, but fragmentation and swelling was seen. Untreated control tissue exhibited up to 15 microm/min of movement of the mitochondria. This could represent normal morphological change, presumably allowing energy transmission across the cell from regions of low to regions of high ATP demand. Lack of mitochondrial movement, fragmentation, and swelling of mitochondria may represent early morphological changes following oxidative stress that may lead to activation of caspase-mediated apoptotic pathways.

Suivi d’un cas de maculopathie solaire par OCT

Solar maculopathy is caused by sun-gazing without protection and in most cases appears to be reversible. Retinal damage may be caused by photochemical changes combined with a rise in temperature at the time of sun observation. We report a case of bilateral solar retinopathy following direct sun gazing after observation of the partial eclipse on 3 October 2005. A 25-year-old Caucasian man presented 24 h after watching the eclipse with symptoms of blurred vision and a bright positive central scotoma. Total direct viewing time was approximately 5 min. While observing the eclipse, the patient kept both eyes open. On presentation, his visual acuity was 20/25 in his right eye and 20/32 in his left eye. Ophthalmoscopic examination revealed a bilateral yellowish-white spot in the center of the foveal region. Static visual field examination did not disclose any absolute scotoma but a decrease in the foveal threshold was noted in both eyes. Optical coherence tomography (OCT) examination revealed a bilateral increased reflectivity of the inner foveal retina that was greater in the left eye. This finding was associated with a hyporeflective area of the underlying retinal pigment epithelium: choriocapillaris complex and an increase in retinal thickness. Eight days later, visual acuity was 20/20 in each eye. Funduscopy showed the yellow lesion had vanished. Four months after exposure, funduscopy was normal and OCT scan showed normal reflectivity of all retinal layers in the fovea. However, static visual field examination disclosed a decreased foveal threshold on the left eye. We compare the OCT findings in this patient with the data reported in the literature. Indeed, various OCT findings have been reported depending on the intensity and frequency of sun exposure. This observation demonstrates that OCT appears to be potentially useful in the evolutive follow-up of solar maculopathy, and emphasizes the importance of eye safety during solar eclipse observation.

Photobleaching of retinal pigment epithelium melanosomes reduces their ability to inhibit iron-induced peroxidation of lipids

Melanin in the human retinal pigment epithelium (RPE) is believed to play an important photoprotective role. However, unlike in skin, melanosomes in the RPE are rather long-lived organelles, which increases their risk of modifications resulting from significant fluxes of light and high oxygen tension. In this work, we subjected purified bovine RPE melanosomes to prolonged aerobic exposure with intense visible and near ultraviolet radiation and studied the effects of irradiation on the melanosome's capacity to inhibit peroxidation of lipids induced by iron/ascorbate. We found that control, untreated melanosomes show a concentration-dependent inhibition of the accumulation of lipid hydroperoxides and the accompanying consumption of oxygen, but photolysed melanosomes lose their antioxidant efficiency and even became prooxidant. The prooxidant action of partially photobleached melanosomes was observed for pigment granules with a melanin content reduced by about 50% compared with untreated melanosomes, as determined by electron spin resonance spectroscopy. We have previously shown that a similar loss in the content of the RPE melanin occurs during human lifetime, which may suggest that the normal antioxidant properties of human RPE melanin become compromised with aging.

Production of a uniform cellular injury by raster scanning of cells for the study of laser bioeffects

Efforts to understand laser bioeffects in cells and tissues have been hindered by a nonuniform cellular response of the specimen, resulting in graded biochemical effects. In addition, the small beam diameters of commonly used lasers limit the number of cells expressing a response to numbers inadequate for the study of biochemical effects. For a limited emission power, expansion of the beam diameter reduces the irradiance, thus requiring longer exposure durations to produce a cellular response. Cultured human retinal epithelial cells were exposed as a single spot ("tophat" exposure) from a carbon dioxide (CO(2)) laser operating at 10.6 microm or scanned with a raster system and compared with thermal injury produced with heated saline for short periods (1-9 s) at relatively high temperature (55-70 degrees C). Cell viability and induction of the 70 kDa heat shock protein were evaluated as indicators of the cellular response. Initial attempts to use a tophat (uniform energy distribution) exposure resulted in a nonuniform cellular response (and nonuniform energy distribution) due to diffraction effects from the 2-mm selection aperture. However, raster scanning for appropriate times with the CO(2) laser yielded uniform cell viability and heat shock protein synthesis that were comparable to dipping cells in heated saline. Because scanning results in a homogeneous exposure of cells, the described scanning technique may be applied to studies of cellular responses to other lasers to evaluate photochemical and photomechanical effects.

Photoprotection of human retinal pigment epithelium cells against blue light-induced apoptosis by melanin free radicals from Sepia officinalis

Cultured retinal pigment epithelium (RPE) cells can phagocytize large foreign particles. Heterogeneous melanin aggregates from Sepia officinalis, a species of cuttlefish, were fed to cultured human RPE cells to produce cells laden with Sepia melanin. Blue light-induced apoptosis (BLIA) assays were performed by flow cytometry on parallel cultures consisting of RPE cells isolated from independent eyes and evenly divided into two cultures, one fed Sepia melanin and one containing only native melanin. After culturing and growth of the cells under blue light illumination for 7 days, the apoptosis percentage of all cultures indicated that Sepia feeding significantly reduced BLIA. To account for Sepia photoprotection, continuous-wave EPR and time-resolved EPR experiments were performed with parallel RPE cultures by using UV (355 nm) and green (532 nm) laser irradiation. Continuous-wave EPR spectra prove that the concentrations of intrinsic and extrinsic melanin free radicals in the Sepia-RPE culture are large compared with those concentrations in the RPE culture. Time-resolved EPR spectra indicate that both UV and green light produced extrinsic melanin radicals as radical pairs from the triplet manifold with a linear dependence on the number of photons per second. These experiments conclusively demonstrate that decreased RPE susceptibility to BLIA correlates with increased intracellular melanin free radical concentrations and that nonnative melanin can supplement native melanin photoprotection of RPE cells.

Evaluation of the safety of xenon/bandpass light in vitrectomy using the A2E-laden RPE model

BACKGROUND

The purpose of the study was to investigate the brightness of the xenon/bandpass light in vitrectomy and assess its phototoxic effects using A2E-laden retinal pigment epithelial (RPE) cells.

METHODS

The total luminous flux and spectral irradiance of 20- and 25-gauge endoilluminators connected to xenon lamps were measured and compared to those of 20- and 25-gauge endoilluminators connected to a halogen lamp. In vitro, A2E-laden cells were evenly exposed to xenon/bandpass light for 5 to 30 min positioned at 1 cm and 2 cm for a standard light probe and an implantable "chandelier" light probe, respectively, above the cells, and the cell viability was assessed using WST-1 assay. The cell viability was compared with cells exposed to 30 min of halogen light projected through a 20-gauge endoilluminator.

RESULTS

The maximal total luminous flux of xenon/bandpass light emitted through the 20-gauge endoilluminator was 2.8 times higher than that of the halogen light. The total luminous flux of the 25-gauge endoilluminators was 0.6-1.1 times greater than the 20-gauge endoilluminators connected to the halogen light. The viability of the A2E-laden cells after exposure to the xenon/bandpass light was no different than that of the cells exposed to the halogen light when the total luminous flux of these lights was at the same level. Xenon/bandpass light from an implantable "chandelier" light probe induced A2E-mediated RPE damage to a similar extent as that of the halogen light through a 20-gauge endoilluminator.

CONCLUSIONS

A2E-mediated phototoxicity of xenon/bandpass light is comparable to that of halogen light.

Photochemical damage of the retina

Visual perception occurs when radiation with a wavelength between 400 and 760 nm reaches the retina. The retina has evolved to capture photons efficiently and initiate visual transduction. The retina, however, is vulnerable to damage by light, a vulnerability that has long been recognized. Photochemical damage has been widely studied, because it can cause retinal damage within the intensity range of natural light. Photochemical lesions are primarily located in the outer layers at the central region of the retina. Two classes of photochemical damage have been recognized: Class I damage, which is characterized by the rhodopsin action spectrum, is believed to be mediated by visual pigments, with the primary lesions located in the photoreceptors; whereas Class II damage is generally confined to the retinal pigment epithelium. The action spectrum peaks in the short wavelength region, providing the basis for the concept of blue light hazard. Several factors can modify the susceptibility of the retina to photochemical damage. Photochemical mechanisms, in particular mechanisms that arise from illumination with blue light, are responsible for solar retinitis and for iatrogenic retinal insult from ophthalmological instruments. Further, blue light may play a role in the pathogenesis of age-related macular degeneration. Laboratory studies have suggested that photochemical damage includes oxidative events. Retinal cells die by apoptosis in response to photic injury, and the process of cell death is operated by diverse damaging mechanisms. Modern molecular biology techniques help to study in-depth the basic mechanism of photochemical damage of the retina and to develop strategies of neuroprotection.

Effects of yellow intraocular lenses on light-induced upregulation of vascular endothelial growth factor

PURPOSE

To investigate the protective effect of a blue-light filtering intraocular lens (yellow IOL) (YA60BB, Hoya) and an ultraviolet (UV)-absorbing IOL (VA60BB, Hoya) on light-induced phototoxicity to retinal pigment epithelial (RPE) cells laden with the lipofuscin fluorophore A2E and on the production of vascular endothelial growth factor (VEGF) after light exposure.

SETTING

University of Tokyo, Tokyo, Japan.

METHODS

The A2E-laden ARPE-19 cells were exposed to white light and a UV-absorbing IOL or a blue-light filtering IOL was placed over the light beam. After 48 hours of irradiation, the viability of the cells was determined with WST-1 (a sodium salt of 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate) assay, and the secreted protein level of VEGF was determined by enzyme-linked immunosorbent assay.

RESULTS

Without an IOL, the white-light exposure decreased cell viability to 28% of the nonirradiated control. Although the UV-absorbing IOL tended to reduce light-induced cell death, the decrease was not significant. However, the presence of the blue-light filtering IOL significantly attenuated light-induced cell damage, increasing cell viability to 42%. The secreted VEGF protein level increased 3.2-fold after the A2E-laden RPE cells were exposed to white light. In the presence of the UV-absorbing IOL, the VEGF protein level decreased, but not significantly. The presence of the blue-light filtering IOL significantly attenuated the upregulated VEGF expression compared to upregulation without an IOL.

CONCLUSION

This study supports the theory that a blue-light filtering IOL may be more protective against A2E-induced photochemical damage and inhibit more light-induced VEGF production than a conventional UV-absorbing IOL.

Damage Thresholds for Exposure to NIR and Blue Lasers in an In Vitro RPE Cell System

PURPOSE

Until reliable nonanimal systems of analysis are available, animal models will be necessary for ocular laser hazard analysis and for evaluating clinical applications. The purpose of this work was to demonstrate the utility of an in vitro system for laser bioeffects by identifying photothermal and photochemical cytotoxicity thresholds for continuous-wave (cw) and mode-locked (ml) laser exposures.

METHODS

Exogenous melanosomes were added to hTERT-RPE1 cells in exposure wells 1 day before laser exposure. Thermal or photochemical laser exposures were delivered to artificially pigmented retinal pigment epithelial (RPE) cultures, with subsequent assay for viability 1 hour after exposure. Beam delivery for the 1-hour photochemical exposures was via a modified culture incubator. The cytoprotective effect of pretreatment with two antioxidants was investigated.

RESULTS

Phagocytosis of melanosomes by the RPE cells was efficient, yielding cultures of uniform pigmentation. The damage threshold for the thermal exposure was consistent with published in vivo results. Thresholds for both blue exposures (cw and ml) were identical. Overnight treatment of cells with ascorbic acid (AA) minimized cell death from both cw and ml blue laser exposure, whereas similar treatment with N-acetyl-L-cysteine (NAC) was less effective.

CONCLUSIONS

The in vitro system described is suitable for measuring meaningful thermal and photochemical laser damage thresholds. The system is also useful in comparative laser bioeffects studies, such as comparisons between cw and ml laser exposures, cells with various degrees of pigmentation, and studies determining the efficacy and mechanisms of treatments altering the response of cells to lasers.

Alcohol- and light-induced electro-oculographic responses in age-related macular degeneration & central serous chorioretinopathy. alcohol- and light-induced EOG responses in ARMD & CSC

The non-photic electro-oculographic (EOG) response induced by alcohol has been proposed as an indicator of retinal pigment epithelial (RPE) integrity, and reported to be abnormal in age-related macular degeneration (ARMD). To evaluate this proposal, we have measured the alcohol-EOG as well as the ISCEV-standard EOG in patients with ARMD (n=11 patients, 4 eyes with drusen, 8 eyes with 'dry' and 7 eyes with 'wet' lesions) and central serous chorioretinopathy (CSC, n=11 patients, 7 eyes with active and 6 eyes with inactive lesions), compared with 29 normal controls. We recorded the alcohol-induced EOG response after a single oral administration of ethanol at 160 mg/kg, followed by an ISCEV-standard EOG. Blood alcohol levels were monitored with a breath analyzer. We found that neither the alcohol-EOG nor the light-induced EOG response showed any difference between either ARMD or CSC patients and normal controls. Nor was there difference among eyes of different ARMD or CSC subgroups. In addition, blood alcohol concentrations near the time of the alcohol-EOG peak showed no obvious relationship with peak/baseline ratios. These data suggest that neither the alcohol- nor the light-induced EOG is a sensitive indicator of these diseases.

Alcohol- and light-induced electro-oculographic responses: variability and clinical utility

The alcohol-induced electro-oculographic (EOG) response has been proposed by Arden as an indicator of retinal pigment epithelial (RPE) integrity. We have evaluated the consistency of the alcohol-EOG with respect to clinical applicability and compared this response to the ISCEV-standard EOG. We recorded, in a group of normal subjects (n=29, 14 men with mean age 42+/-11 years and 15 women with mean age 36+/-13 years), the alcohol response to a single oral dose of ethanol at 160 mg/kg (as 40 proof vodka, drunk in 15 s after 12 h of fasting), followed by an ISCEV-standard EOG 90 min after alcohol administration. Blood alcohol levels were monitored at regular intervals with a breath analyzer. We found a wide range of amplitudes in both light and alcohol responses among participants, from minimal to large values. Subjects had a wide range of blood alcohol concentrations from 0.02 to 0.10%; near the time of the response peak, but there was no relationship between alcohol levels and peak/baseline ratios. In addition, there was no relationship between alcohol peak/baseline ratio and the Arden ratio. Neither the alcohol nor the light response parameters showed any relationship with age or gender. Some of the inter-individual variability in the EOG response to alcohol may reflect variable absorption of oral alcohol. The alcohol-induced EOG has too broad a range of responses to be useful clinically for the one-time evaluation of individual patients. We have similar concerns regarding clinical applications of the standard light-induced EOG.

Cell disintegration by laser-induced transient microbubbles and its simultaneous monitoring by interferometry

Selective retina treatment (SRT) is a novel short pulsed laser therapy of several retinal diseases associated with a decreased metabolism at the retinal pigment epithelium (RPE). The range of laser pulse energies is small, in which the desired selective RPE disintegration is achieved without adverse effects to the neural retina. Thus, a real-time dosimetry control is required. We investigated a noninvasive interferometric technique able to monitor microbubble formation around the intracellular melanin granula, which is the origin of the desired RPE damage. A porcine ex vivo RPE model was irradiated by single pulses (350 ns1.7 mus) of a neodymium: yttrium lithium fluoride laser (527 nm). The specimen was simultaneously probed by a Michelson interferometer (helium neon-laser: 633 nm) and by a hydrophone. Cell viability assays (Calcein-AM) were performed after irradiation. At threshold radiant exposure for cell death (ED(50)=129+/-5 mJ cm2 for 350 ns; ED50=180+/-5 mJ cm2 for 1.7 mus), the interferometric transients changed due to microbubble formation. No major differences in the bubble dynamics were observed between both pulse durations. An algorithm to determine cell death from the interferometric transients showed less than 10% false positive or false negative results for the applied laser expositions compared to the viability assay. Interferometry is a reliable noncontact technique to monitor RPE disintegration and may serve as real-time dosimetry control during SRT.

Pigmented Episcleral Deposits after Brachytherapy of Uveal Melanoma

PURPOSE

To describe the characteristics and evolution of pigmented episcleral deposits after brachytherapy for uveal melanoma to determine their origin and association with melanoma-related mortality.

DESIGN

Noncomparative case series.

PARTICIPANTS

Two hundred eleven patients (108 males, 103 females; median age, 61 years; range, 14-88 years) who were treated with a single ruthenium and iodine plaque therapy (median dose to tumor base, 475 Gy and 392 Gy, respectively) for a choroidal and ciliary body melanoma. Median tumor diameter and height were 12 mm and 5.5 mm, respectively. Eighty-eight patients were treated prospectively during the study.

METHODS

The number and location of pigmented episcleral deposits were recorded under the slit lamp during each visit after brachytherapy. The association of the deposits with tumor characteristics and survival was analyzed with logistic regression and Kaplan-Meier analysis, respectively.

MAIN OUTCOME MEASURES

Number and location of episcleral deposits, melanoma-related mortality.

RESULTS

The pigmented episcleral deposits ranged from black and brownish spots to slightly thickened patches. Most deposits appeared within the first 6 months after brachytherapy. By 1 year, 85% (95% confidence interval, 77-93) of eyes had at least 1 deposit (median, 6). The deposits increased in number until 7 years from irradiation, and decreased with increasing distance from tumor center. An association between the number of deposits at 1 and 2 years and subsequent melanoma-related mortality could not be confirmed (P = 0.80 and P = 0.31, respectively).

CONCLUSIONS

Pigmented macrophage-related episcleral deposits are found in most eyes with uveal melanoma after brachytherapy. Their association with plaque size and isotope rather than with tumor size suggests that radiation atrophy of retinal pigment epithelium and choroid in addition to tumor regression contributes to the formation of the deposits. Knowledge of their existence may save patients from unnecessary enucleation.

A2e mediated phototoxic effects of endoilluminators

AIMS

To compare the theoretical retinal threshold time for endoilluminators and experimental phototoxic effect using A2e laden retinal pigment epithelial (RPE) cells.

METHODS

The spectral irradiances of three types of 20 gauge and 25 gauge endoilluminators, currently commercially available from two manufacturers, were evaluated in conditions where the total beam spectral power was divided by the beam spot size at an estimated use distance of 5 mm from the retina. The retinal threshold time was calculated using the guidelines recommended by the International Commission on Non-Ionizing Radiation Protection. In vitro, A2e laden cells were evenly exposed to light for 30 minutes with a standard endoilluminator positioned 1 cm above the cells and the cell viability was assessed by WST-1 assay.

RESULTS

The retinal threshold times were within 1 minute for all the endoilluminators tested. A significant decrease in the viability of A2e laden RPE cells was observed after they were exposed to light from two of the three 20 gauge endoilluminators. Cell viability was not affected by the exposure to 25 gauge endoilluminators under the same conditions. There was no correlation between the theoretical threshold times and experimental data.

CONCLUSIONS

Light exposure during vitrectomy can induce photochemical damage to the retina. Although the A2e laden RPE model may not correctly mimic a clinical situation, this model may be useful to estimate the possible photochemical damage to RPE cells that could not be deduced by a theoretical retinal hazard model.

The retinitis pigmentosa-mutated RP2 protein exhibits exonuclease activity and translocates to the nucleus in response to DNA damage

Retinitis pigmentosa (RP) is a genetically heterogeneous disease characterized by degeneration of the retina. Mutations in the RP2 gene are linked to the second most frequent form of X-linked retinitis pigmentosa. RP2 is a plasma membrane-associated protein of unknown function. The N-terminal domain of RP2 shares amino acid sequence similarity to the tubulin-specific chaperone protein co-factor C. The C-terminus consists of a domain with similarity to nucleoside diphosphate kinases (NDKs). Human NDK1, in addition to its role in providing nucleoside triphosphates, has recently been described as a 3' to 5' exonuclease. Here, we show that RP2 is a DNA-binding protein that exhibits exonuclease activity, with a preference for single-stranded or nicked DNA substrates that occur as intermediates of base excision repair pathways. Furthermore, we show that RP2 undergoes re-localization into the nucleus upon treatment of cells with DNA damaging agents inducing oxidative stress, most notably solar simulated light and UVA radiation. The data suggest that RP2 may have previously unrecognized roles as a DNA damage response factor and 3' to 5' exonuclease.

Oxidation of A2E Results in the Formation of Highly Reactive Aldehydes and Ketones

It has been reported that the photo-oxidation of A2E, a component of human retinal lipofuscin, leads to products that are toxic to cells via dark reactions. Because these compounds have been implicated in the development of various maculopathies such as age-related macular degeneration (AMD), it is important to determine the structures of those deleterious compounds. Both the photo-oxidation and auto-oxidation of A2E lead to the same complex mixture of products, some of which have lower molecular weights than the staring material. Because A2E is homologous to beta-carotene, it was hypothesized that its oxidation would lead to products analogous to those found in oxidized beta-carotene, namely, a series of cleavage products along the acyclic chain with the concomitant formation of aldehydes. This was found to be the case based upon 1) the formation of all of the aldehydes predicted from the oxidation of beta-carotene, 2) the loss of 28 amu (carbonyl moiety) from the molecular ion, 3) the facile reaction of the aldehydes with nitrophenylhydrazines to form nitrophenylhydrazones and 4) the subsequent MS/MS cleavage of those derivatives at the N-N bond. If formed in vivo, these aldehydes would have toxic effects on any cell. Finally, the similarity in product mixtures from both the photo-oxidation and auto-oxidation strongly suggests that the intermolecular photo-oxidation of A2E results primarily from a radical process without the involvement of singlet oxygen. Any formation of singlet oxygen most likely arises from sensitization by the aldehyde oxidation products, as this process is well known for aldehydes, in general, and retinal, specifically.

Long-term effect of therapeutic laser photocoagulation on gene expression in the eye

Microarray-based gene expression analysis demonstrated that laser photocoagulation (LPC) of mouse eyes had a long-term effect on the expression of genes functionally related to tissue repair, cell migration, proliferation, ion, protein and nucleic acid metabolism, cell signaling, and angiogenesis. Six structural genes, including five crystallins (Cryaa, Cryba1, Crybb2, Crygc, Crygs) and keratin 1-12 (Krt1-12), the anti-angiogenic factor thrombospondin 1 (Tsp1), the retina- and brain-specific putative transcription factor tubby-like protein 1 (Tulp1), and transketolase (Tkt), a key enzyme in the pentose-phosphate pathway, were all shown to be up-regulated by real-time PCR and/or Western blotting. Immunohistochemistry localized five of these proteins to the laser lesions and surrounding tissue within the retina and pigmented epithelium. This is the first study demonstrating long-term changes in the expression of these genes associated with LPC. Therefore, it suggests that modulated gene expression might contribute to the long-term inhibitory effect of LPC. In addition, these genes present novel targets for gene-based therapies aimed at treating microangiopathies, especially diabetic retinopathy, a disease currently only treatable with LPC.

Synthetic carotenoid derivatives prevent photosensitised killing of retinal pigment epithelial cells more effectively than lutein

We studied the photosensitised killing of retinal pigment epithelial (RPE) cells using two photosensitisers that localise in lysosomes. The ARPE-19 cell line was photosensitised using either acridine orange or cis-di(4-sulfonatophenyl)diphenylporphine. We then measured the amount of photoprotection provided to RPE cells by five synthetic carotenoid derivatives and by lutein. The synthetic carotenoid derivatives studied were the Girard's reagent P derivative (GRP) of retinal (GRP-retinal), the GRP derivative of beta-apo-8'-carotenal (GRP-carotenal), the Girard's reagent T derivative of beta-apo-8'-carotenal (GRT-carotenal), the GRP derivative of canthaxanthin ((GRP)2-canthaxanthin) and the dansyl hydrazine derivative of beta-apo-8'-carotenal (dansyl-carotenal). We found that GRP-carotenal, GRT-carotenal (GRP)2-canthaxanthin and dansyl-carotenal were effective photoprotectors. All of these carotenoids had large singlet-oxygen quenching constants and had chemical structures designed to localise either in mitochondria or in lysosomes. In contrast, lutein and GRP-retinal were not effective photoprotectors. The failure of GRP-retinal to provide significant photoprotection may have been due to its relatively low singlet-oxygen quenching constant. Lutein is a potent singlet-oxygen quencher, but may not have provided significant photoprotection in this model because the lutein may have had a different subcellular distribution than the photosensitisers used.

ULTRASTRUCTURAL ANALYSIS OF RABBIT RETINA IRRADIATED WITH A NEW 670-NM DIODE RED LASER AT DIFFERENT POWERS

PURPOSE

Diode lasers have compact dimensions, efficient electric-optical conversion, absence of major cooling requirements, long useful life, and minimal maintenance. We verified the structural and ultrastructural effects of diode red laser emissions at 670 nm on pigmented rabbit retina.

METHODS

Transpupillary laser pulses were applied to rabbit retinas at variable powers with a spot size of 500 microm ( approximately 1,000 microm at the retina level) and duration of 200 milliseconds. Light and electron microscopic analyses were performed.

RESULTS

Subthreshold non-visible lesions were produced using a power of 200 mW. Ophthalmoscopically visible lesions were produced using a power of 400 mW. More prominent lesions were obtained using a higher power (600 mW). Structural and peculiar ultrastructural changes correlated with the power used. In general, damage was incurred by the retinal pigment epithelium with extension into the superficial choroid posteriorly and into the outer retina anteriorly. The inner retina was involved at higher power levels.

CONCLUSIONS

Ultrastructural analysis of rabbit retina treated with the 670-nm diode laser adds newer insights on tissue changes after thermal irradiation. The effects observed are consistent with those reported for the krypton red laser. The 670-nm diode laser is an economic small-size photocoagulator that appears to be a promising modality for transpupillary laser photocoagulation of the retina.

Morphological characteristics of the retinomotor response in salmon trout (oncorhynchus masou) fry in a magnetic field and red light

The retinomotor response was studied in fry of the salmon trout Oncorhynchus masou during experimental exposures to a constant magnetic field and red light alone and together. The responses of photoreceptors and the pigmented epithelium to red light were mesopic in nature. The mesopic state of the retina after exposure of fish to a magnetic field in the dark differed from the pigment epithelium response after exposure to red light. On exposure to the magnetic field after red light, the effects of these two treatments were additive. Rods adapted to low-light conditions, while cones adapted to light. The simultaneous operation of these two mechanisms of perception is thus possible, although it never occurs in normal conditions. On exposure to red light after the magnetic field, the retinomotor response reflected a physiological dysfunction in which neither rods nor cones were operative. The pigmented epithelium is actively involved in responses to changes in the magnetic field. It is suggested that cells of the pigmented epithelium can function as light-sensitive magnetoreceptors.

Molecular and pharmacological characterization of muscarinic receptors in retinal pigment epithelium: role in light-adaptive pigment movements

Muscarinic receptors are the predominant cholinergic receptors in the central and peripheral nervous systems. Recently, activation of muscarinic receptors was found to elicit pigment granule dispersion in retinal pigment epithelium isolated from bluegill fish. Pigment granule movement in retinal pigment epithelium is a light-adaptive mechanism in fish. In the present study, we used pharmacological and molecular approaches to identify the muscarinic receptor subtype and the intracellular signaling pathway involved in the pigment granule dispersion in retinal pigment epithelium. Of the muscarinic receptor subtype-specific antagonists used, only antagonists specific for M1 and M3 muscarinic receptors were found to block carbamyl choline (carbachol)-induced pigment granule dispersion. A phospholipase C inhibitor also blocked carbachol-induced pigment granule dispersion, and a similar result was obtained when retinal pigment epithelium was incubated with an inositol trisphosphate receptor inhibitor. We isolated M2 and M5 receptor genes from bluegill and studied their expression. Only M5 was found to be expressed in retinal pigment epithelium. Taken together, pharmacological and molecular evidence suggest that activation of an odd subtype of muscarinic receptor, possibly M5, on fish retinal pigment epithelium induces pigment granule dispersion.

Selective targeting of the retinal pigment epithelium using an acousto-optic laser scanner

Selective targeting of the retinal pigment epithelium (RPE) is a new strategy for treating certain retinal disorders while preserving adjacent photoreceptors. The treatment currently relies on a complex laser system to produce the required microsecond pulse structure. In our new approach, we scan the focus of a continuous-wave (cw) laser beam with acousto-optic deflectors to produce microsecond-long exposures at each RPE cell. Experiments were performed in vitro with a bench-top scanner on samples of young bovine RPE and in vivo on Dutch belted rabbits with a slit-lamp adapted scanner. Effective dose 50% (ED50) for RPE damage was determined in vitro by fluorescence cell viability assay and in vivo by fluorescein angiography. Damage to individual RPE cells was achieved with laser power on the order of 100 mW. Using separated scan lines, we demonstrate selectivity in the form of alternating lines of dead and surviving cells that resemble the scan pattern. Selectivity is also shown by the absence of retinal thermal coagulation in vivo. Selective RPE damage is feasible by rapidly scanning a cw laser beam. The scanning device is an attractive alternative to conventional laser coagulation and pulsed laser targeting of the RPE.

[The damage of the neural retina and of the retinal pigment epithelium of eyes of rats exposed to highly intensive visible light under alloxanic diabetes]

The experiments on white mongrel rats showed that the light with the intensity of 6000 1x lasting for 6 hours resulted the destruction of the retinal pigment epithelium, of the internal and the external neurosensory cellular processes with subsequent nuclei piknosis and radial glia replacement. On the 7th day after exposure to light focal effusion of the retina corresponding layers. Under the irradiation in diabetes the amount of cells with karyopyknosis increases in 1.6 times in comparision with the findings in case free of diabetes. Was found, that the alloxanic diabetes in its early stage increases the light impairment of the neurosensory cells of the retina.

Time-resolved microspectrofluorimetry and fluorescence lifetime imaging of hypericin in human retinal pigment epithelial cells

Hypericin is the active ingredient of the off-the-shelf antidepressant St. John's Wort. It is an effective phototoxic agent and its systemic administration at therapeutic doses could induce particular damage in the eye due to continuous light exposure. Hypercin is strongly fluorescent and its fluorescence properties can be monitored to investigate noninvasively its localization and interactions. To this aim, time-resolved microspectrofluorimetry and fluorescence lifetime imaging were used to assess the spectral and temporal properties as well as the spatial distribution of the fluorescence emitted by retinal pigment epithelium (RPE) cells treated with Hyp at concentrations in the micromolar range (0.5-10 microM). In the presence of hypericin, the emission peaks at 600-605 nm and the fluorescence decay is best fitted with three lifetimes (5.5-7 ns, 1.9-2.5 ns and <0.8 ns). Spectral and temporal differences were observed between high (> or =5 microM) and low hypericin concentrations. In particular, upon increasing concentration, the emission spectrum of the slow component broadens and its lifetime shortens. The latter change is observed also when high concentrations are reached locally, due to more efficient localization within the cell.

Melanin photoprotection in the human retinal pigment epithelium and its correlation with light-induced cell apoptosis

Time-resolved electron paramagnetic resonance (TREPR) spectroscopy was used to study melanin free radicals in human retinal pigment epithelium (RPE) cells and tyrosine-derived synthetic melanin. TREPR signal traces from RPE cells reveal in vivo light-induced melanin free radical photochemistry in more detail than previously known. Electron spin polarization reflecting a non-Boltzmann population within the energy levels of the spin system is observed in RPE cells as the result of the triplet state photoproduction and subsequent disappearance of free radicals in the melanin polymer. In a set of RPE cells cultured from individual sources, differences in optical absorption, continuous wave EPR spectra, and TREPR signals were correlated with apoptosis assays performed by flow cytometry. Continuous wave EPR spectra of RPE cells and TREPR of acidified synthetic melanin suggest that increased melanin aggregation provides an increase in photoprotection in the RPE cells that are relatively less susceptible to blue light-induced apoptosis.

Anthocyanins protect against A2E photooxidation and membrane permeabilization in retinal pigment epithelial cells

The pyridinium bisretinoid A2E, an autofluorescent pigment that accumulates in retinal pigment epithelial cells with age and in some retinal disorders, can mediate a detergent-like perturbation of cell membranes and light-induced damage to the cell. The photodynamic events initiated by the sensitization of A2E include the generation of singlet oxygen and the oxidation of A2E at carbon-carbon double bonds. To assess the ability of plant-derived anthocyanins to modulate adverse effects of A2E accumulation on retinal pigment epithelium (RPE) cells, these flavylium salts were isolated from extracts of bilberry. Nine anthocyanin fractions reflecting monoglycosides of delphinidin, cyanidin, petunidin and malvidin were obtained and all were shown to suppress the photooxidation of A2E at least in part by quenching singlet oxygen. The anthocyanins tested exhibited antioxidant activity of variable efficiency. The structural characteristics relevant to this variability likely included the ability to form a stable quinonoidal anhydro base at neutral pH, a conjugated diene structure in the C (pyrane) ring, the presence of hydroxyl groups on the B (benzene) ring and the relative hydrophobicity conferred by the arrangement of substituents on the B ring. Cells that had taken up anthocyanins also exhibited a resistance to the membrane permeabilization that occurs as a result of the detergent-like action of A2E.

Sulforaphane induces thioredoxin through the antioxidant-responsive element and attenuates retinal light damage in mice

PURPOSE

Thioredoxin (Trx) is a multifunctional endogenous redox regulator that protects cells against various types of cellular or tissue stresses. This study was conducted to test whether sulforaphane (SF), a naturally occurring isothiocyanate that is highly concentrated in broccoli sprouts, induces Trx in retinal tissues and whether pretreatment with SF protects against light-induced retinal damage in mice.

METHODS

Expression of Trx in mouse retina was analyzed by Western blot and immunohistochemistry. Retinal damage was induced by exposure to white light at 6000 lux for 2 hours. To estimate retinal cell damage, the number of cell nuclei and the percentage of TUNEL-positive cells were counted in the outer nuclear layer and the retinal pigment epithelial (RPE) layer and the electroretinograms recorded. To analyze further the mechanism of Trx induction by SF, cultured human K-1034 RPE cells were used.

RESULTS

Both intraperitoneal and oral SF induced Trx protein in the neural retina and RPE. The maximum induction of Trx was observed with intraperitoneal SF 0.5 mg/d for 3 days. After exposure to light, mice pretreated with SF had a significantly lower percentage of TUNEL-positive RPE and photoreceptor cells, a significantly higher number of RPE and photoreceptor nuclei, and greater amplitude of ERG a- and b-waves than in the saline-treated mice. In K-1034 cells, 1 microM SF induced Trx protein, whereas 10 microM SF did not damage cells or augment cellular peroxide production, tested by a lactate dehydrogenase (LDH) release assay and 2',7'-dichlorofluorescein diacetate (DCFH-DA)/flow cytometry, respectively. In the luciferase reporter assay, the antioxidant-responsive element (ARE) played a role in SF-induced Trx expression. In the electrophoretic mobility shift assay, SF induced binding of Nrf2, small Maf, and c-Jun to the ARE of the Trx gene.

CONCLUSIONS

SF induced Trx in murine retina and effectively reduced retinal light damage. Evidence suggests that the ARE is involved in the mechanism of Trx induction by SF in RPE cells.

Boiling nucleation on melanosomes and microbeads transiently heated by nanosecond and microsecond laser pulses

Selective tissue damage on the cellular level can be achieved by microbubble formation around laser-heated intracellular pigments. To acquire a more detailed understanding of the laser tissue interaction in the highly pigmented retinal pigment epithelium (RPE), we irradiate aqueous suspensions of absorbing microparticles by short pulsed laser irradiation (12 ns, 240 ns, and 1.8 micros). Porcine retinal pigment epithelial melanosomes, gold beads, and magnetic silica beads are used as absorbers. Pulsed laser heating of the particles leads to vaporization of the surrounding liquid. The resulting transient microbubbles on the particle surface are imaged directly on a microscopic level by fast flash light photography. Furthermore, the bubble dynamics is probed by a low power laser. Threshold radiant exposures for bubble formation and nucleation temperatures are experimentally determined. Superheating of the surrounding water to 150 degrees C for melanosomes and to more than 200 degrees C for magnetic silica beads (psi = 3 microm) and gold beads (psi = 500 nm) is achieved. With these data, the absorption coefficient of a melanosome is calculated by thermal modeling of the experimental thresholds for bubble formation.

TIMP-1 production in human retinal pigment epithelial cells after laser exposure

PURPOSE

To investigate changes in the production of tissue inhibitor of metalloproteinase type 1 (TIMP-1) by human retinal pigment epithelial (RPE) cells following argon laser exposure.

METHODS

Human cultured ARPE19 cells were exposed to argon green laser at four different energy levels ranging from 60mW to 360mW. After laser exposure, the culture media were sampled at 0, 24, 72 and 144 hours for TIMP-1 concentration produced by the RPE cells. The levels of TIMP-1 in the cells treated with different laser energy levels were compared with a control group not exposed to laser application. Immunocytochemistry for proliferating cell nuclear antigen (PCNA) was performed to detect any adverse effects on the RPE cells caused by laser exposure.

RESULTS

Immediately after laser exposure, the concentration of TIMP-1 was not detectable. At 24 hours after laser exposure, the concentration of TIMP-1 increased significantly in RPE cells treated with 120mW and 240mW at 24 hours (P=0.006 and P=0.001 respectively) compared with control cells. At 72 hours after treatment, RPE cells treated at 120mW, 240mW and 360mW demonstrated significantly increase in TIMP-1 production compared with control (P=0.003, P < 0.001 and P < 0.001, respectively). No significant reduction in cell viability was observed following laser application as detected by PCNA expression.

CONCLUSIONS

Our results demonstrated that early TIMP-1 production by RPE cells in cell cultures was enhanced following laser exposure.

[The effect of blue light on mitochondrial membrane potential and cytochrome C of cultured human retinal pigment epithelium cells]

OBJECTIVE

To answer the question whether mitochondrial permeability transition (MPT) participates in blue light-induced damage to human retinal pigment epithelium (RPE) cells, this study was directed at assessing the effect of blue light on mitochondrial membrane potential (delta psi(m)) and cytochrome C (Cyt C) of cultured human RPE cells.

METHODS

Human RPE cells were exposed to blue light (wave length 470-490 nm); delta psi(m) was measured by rhodamine 123 staining and subsequent flow cytometry. Three groups were investigated: Group A (exposure to different intensity of blue light); group B (exposure to identical intensity for different duration); group C (exposure to identical intensity and duration, different prolongation of post-exposure culture). Cyt C activity was assayed by ELISA. Caspase-3 was detected by colorimetric assay. In these aspects, two groups were investigated: Group I [(2000+/-500) 1x for 6 h]; Group II [(2000+/-500) 1x for 12 h].

RESULTS

When human RPE cells were exposed to blue light, the more pronounced decrease of delta psi(m) was consistent with the increase of light intensity in group A. Pronounced decrease of delta psi(m) was seen at 6 h and 12 h of exposure duration in group B. At 6 h prolongation of post-exposure culture in group C, the decrease of delta psi(m) was observed, lasting 48 h. The concentration of Cyt C was detected; no significant changes were found at 6 h and 12 h prolongation of post-exposure culture, but a significant increase was found at 24 h and 36 h post-exposure in the two groups. The increase was more significant in Group II than in Group I at 24 h post-exposure. The activity change of caspase-3 was not found in the two groups.

CONCLUSION

Blue light exposure over threshold can induce damage to human RPE cells, probably by triggering the mitochondrial permeability transition, which results in the decrease of delta psi(m) and the release of cytochrome C.

Trypan Blue: Effect on Retinal Pigment Epithelial and Neurosensory Retinal Cells

PURPOSE

To evaluate the toxicity of trypan blue on retinal cells in vitro.

METHODS

Human retinal pigment epithelial cells (ARPE-19) and rat neurosensory retinal cells (R28) were grown in tissue culture and treated with four different concentrations of trypan blue (0.1%, 0.05%, 0.025%, and 0.0125%), in combination with surgical light exposure (0, 5, or 10 minutes). Cell viability, mitochondrial function, and DNA synthesis were measured by trypan blue dye-exclusion assay, mitochondrial dehydrogenase assay, and tritiated [3H] thymidine incorporation, respectively.

RESULTS

ARPE-19 and R28 cells exposed to trypan blue with or without illumination did not show any significant decrease, either in cell viability by the dye-exclusion assay or in [3H] thymidine incorporation. R28 cells exposed to 0.1% trypan blue with and without light showed a significant reduction of mitochondrial dehydrogenase activity (P <0.05). ARPE-19 cells exposed to trypan blue, with or without light, did not show any significant decrease in mitochondrial dehydrogenase activity.

CONCLUSIONS

This study suggests that rat neurosensory retina (R28) cells are more sensitive than human RPE (ARPE-19) cells to trypan blue. ARPE-19 cells showed no evidence of toxicity with any of the three assays, but R28 cells showed evidence of toxicity with the mitochondrial dehydrogenase assay at the higher doses and light-exposure times studied. Clinical studies must be conducted to determine the safety and efficacy of staining of the inner limiting membrane with trypan blue.