[The estimation of age-related sensitivity of the retinal pigment epithelium of Japanese quail (Coturnix japonica) to the light damage]

The effect of blue light damage (445-455 nm, 4 J/cm2) to retinal pigment epithelium (RPE) subcellular structures was investigated in 4 age risk groups (9, 25, 40 and 52 weeks) of Japanese quail Coturnix japonica by light and electron microscopy. The indicator of biological aging of RPE was age-related accumulation of lipofuscin granules: 5-6-fold increase in their quantity increasing by 5-6 times in quails at 52 weeks. The main photo-induced changes observed after 24 h of the photo radiation were located in the blood-retinal barrier, such as loss of homogeneity of Bruch's membrane, disorganization of basal processes, deformations of the nuclei and mitochondria shapes. Those effects ofphotobleaching were more expressed in young birds. But for the older 52-week age birds it was not so noticeable, because their retinal pigment epithelium structures had disorders which were similar to those in younger birds after photodamage.

Hematopoietic stem cells provide repair functions after laser-induced Bruch's membrane rupture model of choroidal neovascularization

Vascular repair by adult hematopoietic stem cells (HSCs) is well-appreciated because these cells are known for their plasticity. We have shown that adult HSCs differentiate into endothelial cells and participate in both retinal and choroidal neovascularization. We asked whether HSCs participated in the wounding response by forming astrocytes, retinal pigment epithelia (RPE), macrophages, and pericytes. Lethally irradiated C57BL6/J mice were reconstituted with HSCs from mice homozygous for green fluorescent protein (GFP) and then subjected to laser-induced rupture of Bruch's membrane. After immunohistochemical examination of ocular tissue, GFP(+) astrocytes were observed concentrated along the edge of the laser wound, where they and mural cells closely ensheathed the neovasculature. GFP(+) vascular endothelial cells and macrophages/microglia were also evident. Large irregularly shaped GFP(+) RPE cells constituted approximately 93% of RPE cells adjacent to the edge of the denuded RPE area. In regions farther away from the wound, GFP(+) RPE cells were integrated among the GFP(-) host RPE. Thus, postnatal HSCs can differentiate into cells expressing markers specific to astrocytes, macrophages/microglia, mural cells, or RPE. These studies suggest that HSCs could serve as a therapeutic source for long-term regeneration of injured retina and choroid in diseases such as age-related macular degeneration and retinitis pigmentosa.

Nitric oxide is proangiogenic in the retina and choroid

Nitric oxide (NO) has been shown to have proangiogenic or antiangiogenic effects depending upon the setting. In this study, we used mice with targeted deletion of one of the three isoforms of nitric oxide synthase (NOS) to investigate the effects of NO in ocular neovascularization. In transgenic mice with increased expression of vascular endothelial growth factor (VEGF) in photoreceptors, deficiency of any of the three isoforms caused a significant decrease in subretinal neovascularization, but no alteration of VEGF expression. In mice with laser-induced rupture of Bruch's membrane, deficiency of inducible NOS (iNOS) or neuronal NOS (nNOS), but not endothelial NOS (eNOS), caused a significant decrease in choroidal neovascularization. In mice with oxygen-induced ischemic retinopathy, deficiency of eNOS, but not iNOS or nNOS caused a significant decrease in retinal neovascularization and decreased expression of VEGF. These data suggest that NO contributes to both retinal and choroidal neovascularization and that different isoforms of NOS are involved in different settings and different disease processes. A broad spectrum NOS inhibitor may have therapeutic potential for treatment of both retinal and choroidal neovascularization.

Retinal damage by light in the golden hamster: an ultrastructural study in the retinal pigment epithelium and Bruch's membrane

The mechanism of the toxicity of light on the retina remains unclear despite a large number of investigations. The purpose of this study is to identify and localize the ultrastructural changes and the site of the earliest damage after intense light exposure. Nine adult Syrian golden hamsters (Mesocricetus auratus) have been maintained under constant illumination with a high-pressure mercury lamp (HQJ R 80 W Deluxe, Osram, Berlin, light intensity 1000 lx) for 12 h, followed by an additional 3 h in the dark. Light damage is assessed by light and electron microscopy. Morphological evaluation reveals focal damage to the retinal pigment epithelial (RPE) cells in close proximity to less-affected RPE cells and normal photoreceptors. Collagen fibers in Bruch's membrane lose their parallel orientation. Occasionally, fusion of cell membranes of neighboring rod outer segments (ROS) is also observed. Continuous, 12 h exposure of hamsters to intense light results in initial focal damage to some RPE cells, such that severely damaged RPE cells are found adjacent to intact RPE cells. Only slight damage to the photoreceptors is evident, suggesting that the sequence of the pathological changes resulting from light begins with damage to the RPE cells and associated Bruch's membrane.

Vascular targeting in photodynamic occlusion of subretinal vessels

PURPOSE

To evaluate the potential of photodynamic therapy (PDT) using benzoporphyrin derivative (BPD) for occlusion of subretinal neovascular membranes, the authors studied efficiency and collateral damage of PDT-induced photothrombosis in the rabbit choriocapillary layer.

METHOD

Benzoporphyrin derivative, a new photosensitizer, currently in clinical trials for tumor therapy, was used. Low-density lipoprotein served as a carrier to enhance selective targeting of vascular endothelial cells.

RESULTS

Complete choriocapillary occlusion was achieved at a BPD dose of 2 mg/kg and a radiant exposure as low as 10 J/cm2. When PDT was performed 3 hours after BPD application, damage to the neural retina was minimal. Only inner photoreceptor segments showed mitochondrial swelling probably secondary to choroidal ischemia. Bruch's membrane remained intact. Retinal pigment epithelium was invariably damaged as seen with other photosensitizers.

CONCLUSION

Compared with photocoagulation BPD-PDT allows endothelial-bound intraluminal photothrombosis, sparing important structures such as neural retina and Bruch's membrane. It may thus provide a more selective treatment of juxtafoveal and subfoveal neovascular membranes.