Changes in manganese superoxide dismutase expression after exposure of the retina to intense light

Suppression of Light-Induced Retinal Degeneration by Quercetin via the AP-1 Pathway in Rats

We examined the cytoprotective effect of quercetin via activator protein (AP-1) and the heat shock protein 70 (Hsp70) pathway against light-induced retinal degeneration in rats. Quercetin was administered intraperitoneally to Sprague-Dawley rats for seven days before light exposure to intense white fluorescent light (3000 lux) for 24 h. Light-induced retinal damage was determined by the number of rows of photoreceptor cell nuclei, the microstructures of the rod outer segments and retinal pigment epithelium, and terminal deoxynucleotidyl transferase (TdT)-mediated 2′-Deoxyuridine-5′-triphosphate (dUTP) nick end labeling. To elucidate the cytoprotective mechanism of quercetin, expression levels were measured in the rat retinas of 8-hydroxy-deoxyguanosine (8-OHdG), a marker of oxidative stress; Hsp70; and transcription factor AP-1 transcription activity. Pretreatment with quercetin inhibited light-induced photoreceptor cellular apoptosis and subsequent retinal degeneration in rats. 8-OHdG and Hsp70 protein expressions were up-regulated markedly by light exposure and suppressed by quercetin pretreatment. The results of an electrophoretic mobility shift assay showed that AP-1-binding activity was activated by light exposure, and binding of c-Fos and c-Jun, but not JunB, mediated the binding activity. Intraperitoneal administration of quercetin decreases photooxidative damage in the retina and mediates cytoprotection against light-induced photoreceptor cell degeneration in rats. Suppression of the heterodimeric combination of c-Jun and c-Fos proteins at the AP-1 binding site is highly involved in quercetin-mediated cytoprotection.

The Involvement of the Oxidative Stress in Murine Blue LED Light-Induced Retinal Damage Model

The aim of study was to establish a mouse model of blue light emitting diode (LED) light-induced retinal damage and to evaluate the effects of the antioxidant N-acetylcysteine (NAC). Mice were exposed to 400 or 800 lx blue LED light for 2 h, and were evaluated for retinal damage 5 d later by electroretinogram amplitude and outer nuclear layer (ONL) thickness. Additionally, we investigated the effect of blue LED light exposure on shorts-wave-sensitive opsin (S-opsin), and rhodopsin expression by immunohistochemistry. Blue LED light induced light intensity dependent retinal damage and led to collapse of S-opsin and altered rhodopsin localization from inner and outer segments to ONL. Conversely, NAC administered at 100 or 250 mg/kg intraperitoneally twice a day, before dark adaptation and before light exposure. NAC protected the blue LED light-induced retinal damage in a dose-dependent manner. Further, blue LED light-induced decreasing of S-opsin levels and altered rhodopsin localization, which were suppressed by NAC. We established a mouse model of blue LED light-induced retinal damage and these findings indicated that oxidative stress was partially involved in blue LED light-induced retinal damage.

Protective effect of light emitting diode phototherapy on fluorescent light induced retinal damage in Wistar strain albino rats

BACKGROUND

Artificial light at night alters retinal physiology. Several studies have shown that light emitting diode phototherapy protects the retina from the damaging effects of acute light exposure.

OBJECTIVE

The aim of this study has been to elucidate the protective effects of 670 nm LED light on retinal damage induced by chronic fluorescent light in Wistar rats.

METHODS

Male Wistar albino rats were divided into four groups: group 1 were control (CL), group 2, 3 and 4 were exposed to fluorescent light (FL), LED preexposure+fluorescent light exposure (LL) and only LED light exposure (OL) respectively. All animals were maintained in their specific exposure regime for 30 days. Fluorescent light of 1800 lx was exposed between 8 pm to 8 am. Rats were exposed to therapeutic LED light of 670 nm of 9 J/cm2 at 25 mW/cm2 for 6 min duration. Histopathological changes in the retina were studied.

RESULTS

Animals of the FL group showed a significant reduction in the outer nuclear layer thickness and cell count in addition to the total thickness of the retina. LL group which were exposed to 670 nm LED prior to exposure to fluorescent light showed a significant decrease in the degree of damage.

CONCLUSIONS

670 nm LED light preexposure is protective to retinal cells against fluorescent light-induced damage.

Suppression of choroidal neovascularization by N-acetyl-cysteine in mice

PURPOSE

N-acetyl-cysteine (NAC) is a potent antioxidant known to be a precursor of glutathione. The purpose of this study was to investigate the role of NAC in the development of choroidal neovascularization (CNV).

METHODS

CNV was induced in C57BL/6 mice by laser photocoagulation of the ocular fundus. Mice were injected intraperitoneally with NAC or vehicle alone. The levels of 4-hydoroxy-2-nonenal (4-HNE)-modified protein and nucleus factor (NF)-κB were determined by wester blotting. The recruitment of macrophages and neutrophils after laser injury was analyzed immunohistochemically and in myeloperoxidase (MPO) assays. Enzyme-linked immunosorbent assays (ELISA) were used to measure monocyte chemotactic protein (MCP)-1, CXCL1, vascular endothelial growth factor (VEGF), VEGF receptor (VEGFR)-1, and VEGFR-2. The extent of CNV was evaluated 7 d after laser injury by lectin staining.

RESULTS

In NAC-treated mice with laser-induced injuries, the induction of 4-HNE-modified protein after 3 hr and the activation of NF-κB in nuclear extracts after 6 hr were markedly suppressed compared to vehicle-treated mice. Macrophage and neutrophil recruitment were inhibited and the levels of MCP-1, CXCL1, VEGF, and VEGFR-1 were also lower in NAC-treated mice compared to vehicle-treated mice. Furthermore, the extent of CNV induced was significantly lower in NAC-treated compared to vehicle-treated mice (p = 0.027).

CONCLUSIONS

Our results clearly showed that NAC inhibited indicators of oxidative stress and the activation of NF-κB induced by laser injury, and, consequently, suppressed macrophage and neutrophil infiltration and the development of CNV. This suggests novel preventative and interventional therapeutic strategies for age-related macular degeneration.

Crocetin prevents retinal degeneration induced by oxidative and endoplasmic reticulum stresses via inhibition of caspase activity

Crocetin is a carotenoid that is the aglicone of crocin, which are found in saffron stigmas (Crocus sativus L.) and gardenia fruit (Gardenia jasminoides Ellis). In this study, we investigated the effects of crocetin on retinal damage. To examine whether crocetin affects stress pathways, we investigated intracellular oxidation induced by reactive oxygen species, expression of endoplasmic reticulum (ER) stress-related proteins, disruption of the mitochondrial membrane potential (ΔΨ(m)), and caspases activation. In vitro, we employed cultured retinal ganglion cells (RGC-5, a mouse ganglion cell-line transformed using E1A virus). Cell damage was induced by tunicamycin or hydrogen peroxide (H(2)O(2)) exposure. Crocetin at a concentration of 3μM showed the inhibitory effect of 50-60% against tunicamycin- and H(2)O(2)-induced cell death and inhibited increase in caspase-3 and -9 activity. Moreover, crocetin inhibited the enzymatic activity of caspase-9 in a cell-free system. In vivo, retinal damage in mice was induced by exposure to white light at 8000lx for 3h after dark adaptation. Photoreceptor damage was evaluated by measuring the outer nuclear layer thickness at 5days after light exposure and recording the electroretinogram (ERG). Retinal cell damage was also detected with Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining at 48h after light exposure. Crocetin at 100mg/kg, p.o. significantly inhibited photoreceptor degeneration and retinal dysfunction and halved the expression of TUNEL-positive cells. These results indicate that crocetin has protective effects against retinal damage in vitro and in vivo, suggesting that the mechanism may inhibit increase in caspase-3 and -9 activities after retinal damage.

Systemic administration of a free radical scavenger, edaravone, protects against light-induced photoreceptor degeneration in the mouse retina

Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a free radical scavenger, is used for the clinical treatment of acute cerebral infarction. In this study, we investigated the protective effects of edaravone against light-induced retinal damage in the mouse. Retinal damage in the mouse was induced by exposure to white light at 8000lx for 3h after dark adaptation. Photoreceptor damage was evaluated by measuring the outer nuclear layer thickness at 5days after the light exposure and recording the electroretinogram (ERG). Retinal cell damage was also detected by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and the expression of 8-hydroxy-2-deoxyguanosine (8-OHdG) and the phosphorylation of mitogen-activated protein kinases (MAPKs) such as extracellular signal regulated protein kinases (ERK), c-Jun N-terminal kinases (JNK), and p38 were analyzed in the retinal samples by immunohistochemistry and immunoblotting. According to evaluation of outer nuclear layer thickness, 3mg/kg, i.p. of edaravone and 1mg/kg. i.v. of edaravone significantly protected against light-induced photoreceptor degeneration at 5days after exposure to light. In ERG measurement, 3mg/kg, i.p. of edaravone inhibited retinal dysfunction at 5days after exposure to light. In addition, 3mg/kg, i.p. of edaravone decreased the numbers of TUNEL-positive cells, 8-OHdG, phosphorylated JNK, and phosphorylated p38, but not that of phosphorylated ERK, in the whole retina at 6h after light exposure. These findings suggest that oxidative stress plays a pivotal role in light-induced retinal damage and that systemic administration of edaravone may slow the progression of photoreceptor degeneration.

Curcumin protects retinal cells from light-and oxidant stress-induced cell death

Age-related macular degeneration (AMD) is a complex disease that has potential involvement of inflammatory and oxidative stress-related pathways in its pathogenesis. In search of effective therapeutic agents, we tested curcumin, a naturally occurring compound with known anti-inflammatory and antioxidative properties, in a rat model of light-induced retinal degeneration (LIRD) and in retina-derived cell lines. We hypothesized that any compound effective against LIRD, which involves significant oxidative stress and inflammation, would be a candidate for further characterization for its potential application in AMD. We observed significant retinal neuroprotection in rats fed diets supplemented with curcumin (0.2% in diet) for 2 weeks. The mechanism of retinal protection from LIRD by curcumin involves inhibition of NF-kappaB activation and down-regulation of cellular inflammatory genes. When tested on retina-derived cell lines (661W and ARPE-19), pretreatment of curcumin protected these cells from H(2)O(2)-induced cell death by up-regulating cellular protective enzymes, such as HO-1, thioredoxin. Since, curcumin with its pleiotropic activities can modulate the expression and activation of many cellular regulatory proteins such as NF-kappaB, AKT, NRF2, and growth factors, which in turn inhibit cellular inflammatory responses and protect cells; we speculate that curcumin would be an effective nutraceutical compound for preventive and augmentative therapy of AMD.

Regulation of thioredoxin by ceramide in retinal pigment epithelial cells

The purpose of this study was to determine the expression, regulation and signaling of a key redoxin family member thioredoxin 1 (Trx1) in normal, oxidant-stimulated and growth factor-pretreated RPE cells. Trx1 is expressed in early passage, human RPE cell cultures. RPE cells exposed to C(2)-ceramide for 24h showed no significant change in expression of Trx1 vs. controls with and without pretreatment for 24h with hepatocyte growth factor (HGF). Neither hypoxia from 1% O(2) or from CoCl(2) exposure resulted in any alteration in Trx1 expression in RPE cells. C(2)-ceramide treatment caused translocation of Trx1 from cytosol to the nucleus, which was abolished by pre-treatment of cells with a p38 MAPK-specific inhibitor. Furthermore, the gene and protein expression of thioredoxin interacting protein (Txnip) increased with ceramide treatment and was significantly (p<0.001) elevated with HGF preincubation vs. untreated controls. Prominent protection from ceramide-induced RPE cell death by exogenous rTrx1 was demonstrated. Although Trx1 directly interacts with its inhibitor, Txnip, p38 inhibition does not appear to have a role in this interaction. We found no direct interaction between apoptosis signal regulating kinase (ASK-1) and Txnip under the same experimental conditions. In summary, our data demonstrate the expression of Trx1 and Txnip in human RPE cells. Ceramide treatment results in translocation of Trx1 to the nucleus, and upregulation of Txnip expression; exogenous rTrx1 protects from ceramide-induced cell death. These results suggest that Trx1 and Txnip play an important role in the response of RPE to ceramide toxicity.

Orally administered epigallocatechin gallate attenuates light-induced photoreceptor damage

EGCG, a major component of green tea, has a number of properties which includes it being a powerful antioxidant. The purpose of this investigation was to deduce whether inclusion of EGCG in the drinking water of albino rats attenuates the effect of a light insult (2200lx, for 24h) to the retina. TUNEL-positive cells were detected in the outer nuclear layer of the retina, indicating the efficacy of the light insult in inducing photoreceptor degeneration. Moreover, Ret-P1 and the mRNA for rhodopsin located at photoreceptors were also significantly reduced as well as the amplitude of both the a- and b-waves of the electroretinogram was also reduced showing that photoreceptors in particular are affected by light. An increase in protein/mRNA of GFAP located primarily to Müller cells caused by light shows that other retinal components are also influenced by the light insult. However, antigens associated with bipolar (alpha-PKC), ganglion (Thy-1) and amacrine (GABA) cells, in contrast, appeared unaffected. The light insult also caused a change in the content of various proteins (caspase-3, caspase-8, PARP, Bad, and Bcl-2) involved in apoptosis. A number of the changes to the retina caused by a light insult were significantly attenuated when EGCG was in the drinking water. The reduction of the a- and b-waves and photoreceptor specific mRNAs/protein caused by light were significantly less. In addition, EGCG attenuated the changes caused by light to certain apoptotic proteins (especially at after 2 days) but did not appear to significantly influence the light-induced up-regulation of GFAP protein/mRNA. It is concluded that orally administered EGCG blunts the detrimental effect of light to the retina of albino rats where the photoreceptors are primarily affected.

Dietary taurine reduces retinal damage produced by photochemical stress via antioxidant and anti-apoptotic mechanisms in Sprague-Dawley rats

Taurine has been shown to be tissue protective in many models of oxidant-induced injury. However, its protective role against retinal damage induced by photochemical stress is less well known. The purpose of the present study was to investigate whether dietary taurine reduced retinal photochemical damage in Sprague-Dawley rats and to further explore the underlying molecular mechanisms of this action. Twenty rats fed AIN-93 formulation and maintained in the dark for 48 h were used as controls (n 20). Another forty rats were randomly divided into two groups and then treated with (n 20) or without 4 % taurine (n 20) for 15 d respectively. After treatment, these two groups were exposed to fluorescent light (3000 +/- 200 lux and 25 degrees C), and the protective effects of dietary taurine were then evaluated. The present results showed that dietary taurine effectively prevented retinal photochemical damage as assessed by changes of morphology. Also, the supplementation caused an increase of taurine in the retina, a decrease of malondialdehyde (P < 0.01), and elevation of superoxide dismutase (P < 0.01) and glutathione peroxidase activities in the retina (P < 0.01). Moreover, dietary taurine inhibited activator protein-1 (AP-1) (c-fos/c-jun subunits) expression (P < 0.05), up regulated NF-kappaB (p65) expression (P < 0.05), and decreased caspase-1 expression (P < 0.05) so as to reduce the apoptosis of photoreceptors in the retina (P < 0.05). These results suggest that dietary taurine reduced retinal damage produced by photochemical stress via antioxidant and anti-AP-1-NF-kappaB-caspase-1 apoptotic mechanisms in rats.

Nitric oxide increases in the rat retina after continuous illumination

Continuous illumination (CI) of the retina induces an oxidative stress followed by the degeneration of photoreceptors. This phenomenon may be partially related to the excessive production of nitric oxide (NO). In order to confirm this hypothesis, the aims of this work are to determine NO levels during the illumination of the retina by electron paramagnetic resonance (EPR), and if an increase of NO is found, to characterize the NOS isoform responsible of the increment by using Western blot. Sprague-Dawley rats were continuously illuminated with white light (12,000 lux) for 2, 24, 48 h, 5 and 7 days while control rats were maintained at light/dark cycles of 12/12 h. Using EPR, an increase of NO signal was observed in the light exposed retinas peaking at 24 h of CI. Western blot analysis showed the expression of iNOS in the illuminated retinas with a peak after 24 h of CI, but did not show significant differences of nNOS among illuminated and control retinas. In summary, there is an increase of NO during CI. Further studies will reveal whether this mechanism is responsible for light induced photoreceptor degeneration.

Light-induced retinal damage involves tyrosine 33 phosphorylation, mitochondrial and nuclear translocation of WW domain-containing oxidoreductase in vivo

WW domain-containing oxidoreductase WOX1, also named WWOX or FOR, is a known proapoptotic protein and a candidate tumor suppressor. Stress stimuli activate WOX1 via tyrosine 33 (Tyr33) phosphorylation and translocation to the mitochondria and nuclei in vitro. Here, the potential role of WOX1 in light-induced retinal degeneration in vivo was investigated. WOX1 is expressed primarily in the inner retina at perinatal stages, whereas an enhanced expression of WOX1, along with its Tyr33 phosphorylation (p-WOX1), is shown specifically in the retinal ganglion cells in adults. Prolonged exposure of mature rats to constant, low-intensity light (500 lux) for 1-2 months resulted in substantial death of photoreceptors and the presence of activated microglia, astrocytes and Muller glial in the outer retina. However, the inner retina was not or barely affected. In the damaged inner and outer nuclear layers of rat retina, WOX1 and p-WOX1 were overly expressed. Also, WOX1 colocalized with fragments of opsin-positive cones. In rd mice with an inherited retinal deficiency, upregulation of WOX1 and p-WOX1 in degenerated retina was observed with age. By electron microscopy, a large number of immunogold particles of WOX1 and p-WOX1 were found in the damaged mitochondria and condensed nuclei of degenerating photoreceptors, indicating that WOX1 undergoes activation and translocation to these organelles. In contrast, little or no WOX1-positive particles were found in the Golgi apparatus. In conclusion, activated WOX1 is likely to exert apoptosis of neuronal cells in the outer retina during the light-induced injury and in mice with an inherited retinal defect.

Distribution of tocopherols and tocotrienols to rat ocular tissues after topical ophthalmic administration

With increasing evidence suggesting the involvement of oxidative stress in various disorders and diseases, the role of antioxidants in vivo has received much attention. Chemically, tocopherols and tocotrienols are closely related; however, it has been observed that they have widely varying degrees of biological effectiveness. The present study has been carried out in an attempt to deepen our understanding of whether there is a significant difference in distribution between tocopherol and tocotrienol homologs to rat eye tissues. Rats were administered 5 microL of pure tocopherol or tocotrienol to each eye once a day for 4 d. Various tissues of the eyes were separated and analyzed for tocopherol and tocotrienol concentrations. The concentration of alpha-to-cotrienol increased markedly in every tissue to which it was administered; however, no significant increase was observed in the case of alpha-tocopherol. The intraocular penetration of gamma-tocopherol and gamma-tocotrienol did not differ significantly. Additionally, a significant increase in total vitamin E concentration was observed in ocular tissues, including crystalline lens, neural retina, and eye cup, with topical administration using a relatively small amount (5 microL) of vitamin E, whereas no significant increase was observed when the same amount of vitamin E was administered orally. Topical administration of tocotrienols is thus an effective way to increase ocular tissue vitamin E concentration.