Cytotoxic effect of spermine on retinal pigment epithelial cells.

PURPOSE: A prior study showed inactivation of ornithine-delta-aminotransferase (OAT)-deficient human retinal pigment epithelial (RPE) cells by a specific irreversible inhibitor (5-fluoromethylornithine; 5-FMO) leading to cell death, in an in vitro model of gyrate atrophy (GA) of the choroid and retina. In the present study, the cytotoxicity of metabolites of ornithine, especially spermine, in RPE cells was investigated, to clarify the mechanism of ornithine cytotoxicity in RPE cells. METHODS: RPE cells were incubated with ornithine or compounds involved in ornithine metabolic pathways. The effects on RPE cell viability and proliferative activity were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric and [(3)H]thymidine incorporation assays. Incorporation of spermine into RPE cells was examined by using [(14)C]spermine and dansyl-spermine. To assess spermine-induced RPE cell death, cells were double stained with annexin V and propidium iodide and subjected to flow cytometry. RESULTS: Ornithine, arginine, glutamate, proline, creatine, glycine, and putrescine exhibited no effects on the viability and proliferative activities of RPE cells, whereas spermidine and spermine (10 mM) inhibited [(3)H]thymidine incorporation by 13% and 89%, respectively. The inhibition of [(3)H]thymidine incorporation by spermine was dose dependent and was observed as early as 4 hours after addition. Further, spermine was incorporated and accumulated in the perinuclear region of RPE cells. Apoptotic RPE cell death was induced by spermine in a dose-dependent manner. CONCLUSIONS: The present results demonstrated that excessive spermine is cytotoxic to RPE cells and suggest that metabolites of ornithine, especially spermine, may be involved in the mechanism of RPE degeneration in GA.

[Retinal pigment epithelial cells contribute to maturation and fenestration of the vascular endothelial cells in vascular endothelial growth factor-transgenic mice].

PURPOSE: To demonstrate the role of the retinal pigment epithelial cells (RPE) in subretinal neovascularization during maturation and fenestration of endothelial cells in vascular endothelial growth factor (VEGF) transgenic mice. METHODS: VEGF transgenic mice were given an intraperitoneal injection of 50 mg/kg of sodium iodate (treated) or physiological saline (controls) on postnatal day 10. Fluorescein angiography (FAG) was carried out and the mice were sacrificed on postnatal day 31. The eyes were removed and processed for light and electron microscopy. RESULTS: FAG showed leakage from neovascularization in both groups, but there were fewer leakages in the treated group than in the control group. Electron microscopy showed subretinal neovascularization in both groups, but there were fewer fenestrations and less maturity of endothelial cells in the new vessels of mice in the treated group. In the treated mice, damaged RPE cells did not completely enclose new vessels and the endothelial cells were immature. CONCLUSIONS: It is suggested that RPE cells promote endothelial cell maturation and formation of fenestrations in VEGF-induced subretinal neovascularization.

RPE cells modulate subretinal neovascularization, but do not cause regression in mice with sustained expression of VEGF.

PURPOSE: Previous studies using models of choroidal neovascularization (CNV) in which the angiogenic stimulus is not sustained, have concluded that the retinal pigmented epithelium (RPE) causes regression of neovascularization (NV). However, the withdrawal of angiogenic stimuli may actually be the major modulator of NV, and RPE cells may simply be responding to withdrawal of the angiogenic stimuli or something released by NV because of the withdrawal. In this study, the long-term course of NV and the behavior of the RPE in rhodopsin/VEGF transgenic mice, in which there is a sustained angiogenic stimulus, was investigated. METHODS: Hemizygous mice from the V-6 line were killed at 0.75, 1, 3, 6, and 12 months after birth, and at each time point mRNA for VEGF, VEGF-R1, and VEGF-R2 was measured by RT-PCR. Some mice were perfused with fluorescein-labeled dextran and retinal flatmounts were examined by fluorescence microscopy. Light and electron microscopy was performed on Epon-embedded eyes. RESULTS: The mRNA levels for VEGF, VEGF-R1, and VEGF-R2 remained constant from the earliest to the latest time point. Retinal flatmounts showed numerous small areas of subretinal NV at 3 weeks and at 1 month, and there were a similar number of larger lesions. By 6 months, many of the individual NV lesions had grown together to form large networks of new vessels. At 12 months, NV networks were similar to those at 6 months, but some of the vessels were not perfused. Light microscopy showed serous retinal detachments overlying NV lesions in mice up to 3 months of age, but at 6 and 12 months, the RPE completely surrounded new vessels and formed tight junctions to reestablish the outer blood-retinal barrier, and there were no serous detachments. Electron microscopy showed that compared with more acute NV lesions, chronic lesions contained thinner endothelial cells, similar to those of the choriocapillaris in that they had scant cytoplasm and numerous fenestrations, or pinocytotic vesicles with thick basement membrane surrounded by extracellular matrix (ECM). Bruch's membrane remained intact. CONCLUSIONS: Despite persistent high expression of VEGF and its receptors, NV stopped growing and reached a plateau in older V-6 mice. RPE cells modulated the NV by surrounding it and reestablishing the blood-retinal barrier, but did not cause regression, although some vessels in chronic lesions were not perfused. These data do not support the conclusion of several previously reported studies, that RPE cells cause regression of CNV.

Prevention of ornithine cytotoxicity by nonpolar side chain amino acids in retinal pigment epithelial cells.

PURPOSE: To investigate the effect of amino acids on ornithine cytotoxicity in ornithine-delta-aminotransferase (OAT)-deficient human retinal pigment epithelial (RPE) cells as an in vitro model of gyrate atrophy (GA) of the choroid and retina. METHODS: RPE cells were treated with 0.5 mM 5-fluoromethylornithine (5-FMOrn), a specific and irreversible OAT inhibitor. OAT-deficient RPE cells were incubated with 10 mM ornithine in the presence of 20 mM of 1 of 18 amino acids or 10 mM 2-amino-2-norbornane-carboxylic acid (BCH), a conventional inhibitor of the amino acid transporter system L. Ornithine cytotoxicity and cytoprotective effects of each amino acid was evaluated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay 72 hours after treatment with ornithine in OAT-deficient RPE cells. Ornithine incorporation into RPE cells was evaluated using DL-[14C]ornithine. RESULTS: An MTT colorimetric assay revealed that small and large zwitterionic amino acids, but not acidic or basic amino acids, decreased ornithine cytotoxicity in OAT-deficient RPE cells. Incorporation of DL-[14C]ornithine by RPE cells decreased to 79% of the control level after incubation for 48 hours with 20 mM leucine, the most effective cytoprotective amino acid. Further, BCH prevented ornithine cytotoxicity in a dose-dependent manner. Both light and heavy chains of L-type amino acid transporter (LAT)-1, LAT2, y+LAT1, and 4F2hc were expressed in RPE cells. CONCLUSIONS: The present results demonstrate that L-type amino acid transporter(s) may be involved in protection against ornithine cytotoxicity in human RPE cells. Thus, amino acid transportation in RPE cells may be a good target for a new therapy for GA as well as other kinds of chorioretinal degeneration.

Polypoidal choroidal vasculopathy: incidence, demographic features, and clinical characteristics.

OBJECTIVE: To clarify the incidence, demographic features, and clinical characteristics of polypoidal choroidal vasculopathy (PCV) in Japanese patients. METHODS: Consecutive patients with presumed neovascular age-related macular degeneration (AMD) who met the eligibility criteria were examined between January 1, 1999, and October 31, 2001. All patients underwent complete ophthalmologic examination and fluorescein and indocyanine green angiography. RESULTS: Among 471 eyes of 418 patients who met the criteria, 110 eyes (23%) of 100 patients were diagnosed as having PCV and 361 eyes (77%) of 318 patients as having neovascular AMD. Mean age of patients with PCV was 68.4 years, with a male preponderance (63% of patients); involvement was mostly unilateral (90% of patients), and polypoidal vascular lesions were located mainly in the macula (85% of eyes). Retinal manifestations of PCV were characterized by serous macular detachment (52% of eyes), submacular hemorrhage (30% of eyes), and retinal pigment epithelium degeneration (10% of eyes). There were few subretinal fibrovascular proliferations (7% of eyes). Mean visual acuity was 0.31 in eyes with PCV and 0.18 in eyes with AMD. The incidence of severe visual loss (0.2 or worse) was 35% in PCV and 53% in AMD. CONCLUSIONS: The incidence of PCV in Japanese patients is high, and the incidence and demographic features vary in different ethnic groups. The clinical manifestations of PCV and AMD resemble each other; however, PCV is characterized by low incidence of subretinal fibrovascular proliferation, slow progression of vascular abnormality, and minimal association with conventional choroidal neovascularization. These factors seem to lead to a more favorable visual outcome in PCV compared with neovascular AMD.

Expression of transforming growth factor-beta receptors in normal rat retina and experimental choroidal neovascularization.

PURPOSE: Transforming growth factor-beta (TGF-beta) plays an important role in the development of choroidal neovascularization. TGF-beta transduces signals through the mediation of type I and type II receptors. We investigated the expression of TGF-beta receptors in a normal rat retina and a model of experimentally induced choroidal neovascularization. METHODS: Choroidal neovascularization was induced by laser photocoagulation in rat eyes. The expression of TGF-beta receptors was determined using immunohistochemical and in situ hybridization methods. RESULTS: In normal adult rat retinas, immunoreactivity and mRNA expression of TGF-beta receptor type I (TbetaRI) and TGF-beta receptor type II (TbetaRII) were found in the ganglion cells. During the process of neovascularization, immunoreactivity and mRNA expression of TbetaRI and TbetaRII were widely distributed in laser lesions soon after photocoagulation; thereafter, these receptors were specifically detected in the endothelial cells of choroidal neovascularization. CONCLUSIONS: The expression of TGF-beta receptors in normal rat retinas suggests that TGF-beta plays an important role in the homeostasis of normal retina. The upregulation of TGF-beta receptors in choroidal neovascularization strongly suggests that TGF-beta is most likely transduced through specific receptors and plays an important role in the development of choroidal neovascularization.

Uveitis in sarcoidosis.

Sarcoid uveitis is common, mostly in a chronic form, and is prevalent in women past middle age. The onset is insidious. Inflammation is commonly mild but persists for a long period and then is complicated by the development of macular edema, cataract, and glaucoma, resulting in visual loss. The diagnosis is made according to characteristic ocular signs and systemic investigations. Effective treatment consists primarily of long-term use of steroids. Nonetheless, 15% of cases of sarcoid uveitis demonstrate an unfavorable visual outcome.

Effects of local administration of interferon-beta on proliferation of retinal pigment epithelium in rabbit after laser photocoagulation.

PURPOSE: To investigate whether local administration of interferon (IFN)-beta promotes proliferation of the retinal pigment epithelium (RPE) in vivo. METHODS: Following local injection of IFN-beta into the sub-Tenon space of rabbit eyes, the penetration of IFN-beta into various intraocular areas was determined by means of enzyme-linked immuno-adsorbent assay. Retinal lesions were produced by laser photocoagulation (PC), and IFN-beta (1 x 10(6) IU, 1 x 10(5) IU, or 1 x 10(4) IU) was administered into the sub-Tenon space. Physiological saline was substituted for IFN-beta in controls. The proliferation of RPE cells was inspected histopathologically. RESULTS: After IFN-beta administration, IFN-beta was found in all intraocular areas examined, with the highest concentration detected in the choroid. After PC, profuse proliferation of RPE cells began earlier in the rabbits that received the highest dose of IFN-beta than in the control rabbits; repair of the central part of the coagulated lesion in those rabbits was complete within 7 days after PC. In control rabbits, the histopathologic wound repair process proceeded more slowly and to a limited extent. Proliferation of RPE cells in the low and medium dose IFN-beta-treated rabbits was similar to that in the control rabbits. CONCLUSION: The present study demonstrates that repair of the PC-induced retinal lesions, particularly the proliferation of RPE cells, is promoted in vivo by local administration of IFN-beta.

Polypoidal choroidal vasculopathy: natural history.

PURPOSE: The present study was performed to clarify the long-term natural history of polypoidal choroidal vasculopathy (PCV). DESIGN: Prospective, consecutive observational case series. METHODS: Fourteen eyes of 12 consecutive patients with PCV were prospectively followed in our clinic for at least 2 years without any treatment after a first visit to the clinic between February 1996 and November 1998. All patients underwent complete ophthalmologic examination, color fundus photography, and fluorescein and indocyanine green (ICG) angiography at regular intervals. Inclusion criteria were as follows: eyes had serous and/or hemorrhagic pigment epithelium detachment (PED) and retinal detachment in the posterior pole, and ICG angiography revealed a branching vascular network with polypoidal dilations at the terminals of the network. Exclusion criteria were as follows: other diseases such as exudative age-related macular degeneration, high myopia, angioid streaks, and presumed ocular histoplasmosis syndrome, and patients who previously underwent any ocular surgery. RESULTS: Patients were followed for mean of 39.9 months (range, 24-54 months). PCV was present in 10 (83%) men and two women and in the elderly (mean age 68.1 years), usually unilateral (83%) with vascular lesions located at the macula (93%). The PCV manifested in two patterns, exudative and hemorrhagic. In the exudative pattern, serous PED and retinal detachment were predominant at the macula. The hemorrhagic pattern was characterized by hemorrhagic PED and subretinal hemorrhage at the macula. ICG angiography revealed polypoidal choroidal neovascularization that was changeable in appearance and repeatedly grew and spontaneously regressed, but the vascular network persisted. In some eyes, a collection of small aneurysmal dilations of vessels resembling a cluster of grapes appeared and all of them had marked bleeding and leakage and worse outcome. CONCLUSION: Polypoidal choroidal vasculopathy is a long persistent chronic disease and the patients had a variable course. Fifty percent of the patients had a favorable course. In the remaining half of the patients, the disorder persisted for a long time with occasional repeated bleeding and leakage, resulting in macular degeneration and visual loss. Eyes with a cluster of grapes-like polypoidal dilatations of the vessels had a high risk for severe visual loss.

[Clinical dose finding study of indocyanine green to detect choroidal neovascularization in patients with exudative age-related macular degeneration].

PURPOSE: To evaluate the proper clinical dosage of indocyanine green(ICG) in angiography for detecting choroidal neovascularization(CNV) of exudative age-related macular degeneration(AMD). SUBJECTS AND METHODS: Indocyanine green angiography (IA) was performed using a randomized crossover method with two different doses on two occasions. Ease of detection, side effects and clinical serum data were also evaluated. RESULTS: Among the 39 eyes, detection of CNV using 12.5 mg and 25 mg was most effective in 21 and 31 eyes respectively, showing a statistically significant difference. Slight vomiting was observed temporarily in one patient who had taken 25 mg. CONCLUSION: A dose of 25 mg is appropriate for detection of CNV of exudative AMD and this dosage raises no safety concerns.