Entangled Pure State Transformations via Local Operations Assisted by Finitely Many Rounds of Classical Communication

We consider generic pure n-qubit states and a general class of pure states of arbitrary dimensions and arbitrarily many subsystems. We characterize those states which can be reached from some other state via local operations assisted by finitely many rounds of classical communication (LOCC_{N}). For n qubits with n>3, we show that this set of states is of measure zero, which implies that the maximally entangled set is generically of full measure if restricted to the practical scenario of LOCC_{N}. Moreover, we identify a class of states for which any LOCC_{N} protocol can be realized via a concatenation of deterministic steps. We show, however, that in general there exist state transformations which require a probabilistic step within the protocol, which highlights the difference between bipartite and multipartite LOCC.

The Mitochondrial-Derived Peptide Humanin Protects RPE Cells From Oxidative Stress, Senescence, and Mitochondrial Dysfunction

PURPOSE

To investigate the expression of humanin (HN) in human retinal pigment epithelial (hRPE) cells and its effect on oxidative stress-induced cell death, mitochondrial bioenergetics, and senescence.

METHODS

Humanin localization in RPE cells and polarized RPE monolayers was assessed by confocal microscopy. Human RPE cells were treated with 150 μM tert-Butyl hydroperoxide (tBH) in the absence/presence of HN (0.5-10 μg/mL) for 24 hours. Mitochondrial respiration was measured by XF96 analyzer. Retinal pigment epithelial cell death and caspase-3 activation, mitochondrial biogenesis and senescence were analyzed by TUNEL, immunoblot analysis, mitochondrial DNA copy number, SA-β-Gal staining, and p16INK4a expression and HN levels by ELISA. Oxidative stress-induced changes in transepithelial resistance were studied in RPE monolayers with and without HN cotreatment.

RESULTS

A prominent localization of HN was found in the cytoplasmic and mitochondrial compartments of hRPE. Humanin cotreatment inhibited tBH-induced reactive oxygen species formation and significantly restored mitochondrial bioenergetics in hRPE cells. Exogenous HN was taken up by RPE and colocalized with mitochondria. The oxidative stress-induced decrease in mitochondrial bioenergetics was prevented by HN cotreatment. Humanin treatment increased mitochondrial DNA copy number and upregulated mitochondrial transcription factor A, a key biogenesis regulator protein. Humanin protected RPE cells from oxidative stress-induced cell death by STAT3 phosphorylation and inhibiting caspase-3 activation. Humanin treatment inhibited oxidant-induced senescence. Polarized RPE demonstrated elevated cellular HN and increased resistance to cell death.

CONCLUSIONS

Humanin protected RPE cells against oxidative stress-induced cell death and restored mitochondrial function. Our data suggest a potential role for HN therapy in the prevention of retinal degeneration, including AMD.

Inhibition of DNA Methylation and Methyl-CpG-Binding Protein 2 Suppresses RPE Transdifferentiation: Relevance to Proliferative Vitreoretinopathy

PURPOSE

The purpose of this study was to evaluate expression of methyl-CpG-binding protein 2 (MeCP2) in epiretinal membranes from patients with proliferative vitreoretinopathy (PVR) and to investigate effects of inhibition of MeCP2 and DNA methylation on transforming growth factor (TGF)-β-induced retinal pigment epithelial (RPE) cell transdifferentiation.

METHODS

Expression of MeCP2 and its colocalization with cytokeratin and α-smooth muscle actin (α-SMA) in surgically excised PVR membranes was studied using immunohistochemistry. The effects of 5-AZA-2'-deoxycytidine (5-AZA-dC) on human RPE cell migration and viability were evaluated using a modified Boyden chamber assay and the colorimetric 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assay. Expression of RASAL1 mRNA and its promoter region methylation were evaluated by real-time PCR and methylation-specific PCR. Effects of 5-AZA-dC on expression of α-SMA, fibronectin (FN), and TGF-β receptor 2 (TGF-β R2) and Smad2/3 phosphorylation were analyzed by Western blotting. Effect of short interfering RNA (siRNA) knock-down of MeCP2 on expression of α-SMA and FN induced by TGFβ was determined.

RESULTS

MeCP2 was abundantly expressed in cells within PVR membranes where it was double labeled with cells positive for cytokeratin and α-SMA. 5-AZA-dC inhibited expression of MeCP2 and suppressed RASAL1 gene methylation while increasing expression of the RASAL1 gene. Treatment with 5-AZA-dC significantly suppressed the expression of α-SMA, FN, TGF-β R2 and phosphorylation of Smad2/3 and inhibited RPE cell migration. TGF-β induced expression of α-SMA, and FN was suppressed by knock-down of MeCP2.

CONCLUSIONS

MeCP2 and DNA methylation regulate RPE transdifferentiation and may be involved in the pathogenesis of PVR.

Maximally entangled set of multipartite quantum states

Entanglement is a resource in quantum information theory when state manipulation is restricted to local operations assisted by classical communication (LOCC). It is therefore of paramount importance to decide which LOCC transformations are possible and, particularly, which states are maximally useful under this restriction. While the bipartite maximally entangled state is well known (it is the only state that cannot be obtained from any other and, at the same time, it can be transformed to any other by LOCC), no such state exists in the multipartite case. In order to cope with this fact, we introduce here the notion of the maximally entangled set (MES) of n-partite states. This is the set of states which are maximally useful under LOCC manipulation; i.e., any state outside of this set can be obtained via LOCC from one of the states within the set and no state in the set can be obtained from any other state via LOCC. We determine the MES for states of three and four qubits and provide a simple characterization for them. In both cases, infinitely many states are required. However, while the MES is of measure zero for 3-qubit states, almost all 4-qubit states are in the MES. This is because, in contrast to the 3-qubit case, deterministic LOCC transformations are almost never possible among fully entangled four-partite states. We determine the measure-zero subset of the MES of LOCC convertible states. This is the only relevant class of states for entanglement manipulation.

Angiopoietin-1 upregulation by vascular endothelial growth factor in human retinal pigment epithelial cells

PURPOSE

To determine whether vascular endothelial growth factor (VEGF) regulates angiopoietin (Ang)-1 and -2 expression in retinal pigment epithelial (RPE) cells.

METHODS

Expression of VEGF, Ang1, and Ang2 in surgically removed human choroidal neovascular membranes (CNVMs) was analyzed by double-label confocal immunofluorescence microscopy. Total RNA was extracted from cultured human RPE cells treated with VEGF for mRNA analysis. Northern blot analysis was performed to examine the time course and dose response of Ang1 and Ang2 mRNA expression. mRNA stability and nuclear run-on analyses were performed. Secreted Ang1 and Ang2 protein levels in conditioned media from RPE cells were examined by Western blot analysis.

RESULTS

Ang1 and Ang2 immunostaining colocalized with VEGF-positive stromal cells in human CNVMS: Ang1 and Ang2 mRNAs were expressed by cultured serum-starved RPE cells. VEGF upregulated Ang1 mRNA in a time- and dose-dependent manner without a significant change in Ang2 mRNA. Ang1 and Ang2 mRNAs in RPE cells were as stable as that of S18. VEGF stimulation further increased the half-life of Ang1 mRNA, but did not alter its transcription rate. VEGF increased the amount of Ang1, but not Ang2, protein secreted into the medium.

CONCLUSIONS

The colocalization of Ang1 and Ang2 with VEGF in CNVM stromal cells and the upregulation of Ang1 expression by VEGF in cultured RPE cells suggest that VEGF may selectively modulate Ang expression during CNV.

The possibility of gene therapy for the treatment of choroidal neovascularization

PURPOSE

Choroidal neovascularization (CNV) is responsible for most cases of severe visual loss in age-related macular degeneration. Recently, the possibility of gene therapy has been proposed for the treatment of CNV. The purpose of this study was to examine the feasibility of ex vivo and in situ gene therapy approaches for CNV.

DESIGN

Experimental study.

METHODS

Human retinal pigment epithelial (RPE) cells were transduced with a retroviral vector coding for beta-galactosidase. Transduced cells were grown on type II collagen sheets and transplanted under the retina of 20 rabbits. Animals were observed for 3 to 56 days, and transplanted cells were examined histologically and with X-gal staining. Bovine choroidal endothelial cells (CEC) were transduced with retroviral vectors coding for tissue inhibitor of metalloproteinase-2 (TIMP-2) or control vector. Production of TIMP-2 by transduced cells was determined by immunohistochemical analysis and enzyme-linked immunosorbent assay. Effect of transduction on in vitro proliferation, migration, and tube formation was examined in response to vascular endothelial growth factor (VEGF). Four CNV lesions were induced in one cynomolgus monkey by laser photocoagulation. Two days later, retroviral vector coding for TIMP-2 or control vector was injected into the subretinal space overlying the CNV lesions. The monkey was observed for 12 weeks using fluorescein angiography.

RESULTS

Transplantation of transduced RPE cells was technically achieved in 10 of 20 animals. In these animals, RPE cells at the site of transplantation formed a monolayer and expressed beta-galactosidase for 14 days. beta-Galactosidase-positive cells were not identified at 56 days. Choroidal endothelial cells transduced with TIMP-2 secrete TIMP-2 into the media and show decreased migration and tube formation in vitro. In the in vivo monkey model, the control CNV lesions (n = 2) showed prominent leakage, whereas the experimental lesions (n = 2) showed minimal hyperfluorescence.

CONCLUSIONS

Retrovirally transduced RPE cells survive in the subretinal space for at least 14 days and continue to express the gene product coded for by the vector. Choroidal endothelial cells retrovirally transduced for TIMP-2 produce TIMP-2 in vitro and show decreased angiogenic responses in vitro in response to VEGF. A preliminary study attempting in situ delivery of TIMP-2 vector to CNV lesions in a monkey eye supports the feasibility of this approach and encourages further study.

Natural history of choroidal neovascularization induced by vascular endothelial growth factor in the primate

BACKGROUND

A new model of choroidal neovascularization (CNV) has been developed in the primate by implanting vascular endothelial growth factor (VEGF)-impregnated microspheres in the subretinal space.

METHODS

CNV was induced in Macaca mulatta monkeys by implanting VEGF-impregnated gelatin microspheres in the subretinal space. Progression of CNV was followed for 24 weeks after surgery using fluorescein angiography. Eyes were enucleated at various time points, and lesions were evaluated for evidence of CNV by light microscopy and by immunohistochemical staining.

RESULTS

CNV developed in 12 (92%) of 13 eyes. Fluorescein leakage was first observed in the 2nd postoperative week and was apparent for the following 12 weeks. CD31 staining for endothelial cells was first observed at day 7 and was evident for the following 8 weeks. Glial fibrillary acidic protein staining revealed a glial adhesion between the proliferative membrane and the retina at 6 weeks after implantation. Smooth muscle actin-positive cells were found a +2 weeks and remained prominent for at least the next 6 weeks. Cytokeratin-positive retinal pigment epithelial (RPE) cells, first identified in the proliferative membrane at day 3, predominated throughout the growth of the membrane. Macrophages (RAM-II positive) were present at day 3 but were no longer observed after day 7.

CONCLUSION

In monkeys, subretinal implantation of VEGF-impregnated gelatin microspheres leads to the development of CNV. Early, disciform and reparative stages of CNV were observed, similar to those seen in humans. This model will be useful for studying the pathogenesis of CNV and for evaluating potential treatment strategies.

A distinct integrin-mediated phagocytic pathway for extracellular matrix remodeling by RPE cells

PURPOSE

To characterize the phagocytosis of extracellular matrix components by retinal pigment epithelial cells and to determine which receptors and signal transduction pathways are involved.

METHODS

Fluorescent latex beads were coated with fibronectin (FN), collagen type I or IV, or thrombospondin and incubated with human retinal pigment epithelial cells for 3 hours. Phagocytosis was quantified by flow cytometry. The effects of adhesion blocking antibodies to cell surface receptors (alpha1, alpha3, alpha5, beta1, alpha5beta1, alphavbeta3, alphavbeta5 integrins and CD36) and inhibitors of specific intracellular signaling pathways (tyrosine kinase phosphatidylinositol 3-kinase [PI3-kinase], protein kinase C [PKC], and mitogen-activated protein kinase) were determined using FN-coated beads.

RESULTS

Phagocytosis of FN-coated beads was greater than phagocytosis of beads coated with collagen type I, collagen type IV, or thrombospondin or uncoated controls (P < 0.0005). Anti-alpha5, -beta1, and -alpha5beta1 antibodies markedly inhibited FN phagocytosis (P < 0.0005); the inhibitory effects of anti-alpha5 antibody were stronger in the initial stages (binding) than in the later stages (internalization) of phagocytosis. There was no significant effect on phagocytosis when anti-alpha1, -alpha3, -alphavbeta5, -alphavbeta3 or -CD36 antibodies were used. Fibronectin phagocytosis was decreased by inhibitors of tyrosine kinase (genistein, 100 microg/ml, P < 0.005) and PI3-kinase (wortmannin, 5 microM, P < 0.01), but these reagents did not affect the uncoated controls. The PKC inhibitor calphostin C (400 nM) nonspecifically increased the phagocytosis of FN-coated (P < 0.05) and uncoated beads (P < 0.01).

CONCLUSIONS

Subconfluent retinal pigment epithelial cells preferentially phagocytose FN over other extracellular matrix components. Phagocytosis of FN utilizes the alpha5beta1 integrin, is mediated in part through tyrosine kinase and PI3-kinase signaling pathways, and is modulated by PKC. Phagocytosis of extracellular matrix by retinal pigment epithelial cells may represent a novel mechanism for remodeling of the provisional extracellular matrix during outer retinal wound healing.

Transplantation of autologous iris pigment epithelium to the subretinal space in rabbits

BACKGROUND

Transplantation of autologous iris pigment epithelium (IPE) into the subretinal space has been suggested as one approach for the treatment of age-related macular degeneration. Autologous rabbit IPE cells were transplanted to the subretinal space to define the technique of transplantation and examine the survival of the transplanted cells.

METHODS

Autologous IPE cells were harvested by iridectomy and transplanted directly to the subretinal space of the fellow eye in 25 rabbits, using the parsplana approach. Animals were killed over a period of 5 months, and the retinas were examined morphologically by light and electron microscopy.

RESULTS

Autologous IPE cells survived and formed a polarized monolayer above the retinal pigment epithelium in the subretinal space, with apical microvilli adjacent to photoreceptors. Fragments of phagocytosed photoreceptor rod outer segments were observed in phagosomes in the cytoplasm of IPE cells. Adjacent rod outer segments remained healthy throughout the experimental period. No signs of a cell-mediated immunologic response were observed.

CONCLUSIONS

Our results show that in rabbits, autologous IPE cells transplanted to the subretinal space survive and do not adversely affect the photoreceptors. These results suggest that in humans, IPE cells might provide a substitute for retinal pigment epithelium cells as autologous transplants for the treatment of age-related macular degeneration.

Retinal pigment epithelial cells are heterogeneous in their expression of MHC-II after stimulation with interferon-gamma

The pattern of interferon-gamma-induced major histocompatibility complex Class II antigen expression was evaluated on the retinal pigment epithelium. Experiments were performed in vitro using explant cultures of aged and fetal human eyes and in vivo in albino rabbits. The human explants were stimulated with 50 U ml-1 interferon-gamma for 3 days prior to immunostaining for Class II. The rabbit eyes were subretinally injected in vivo with 50 microl of interferon-gamma (500 U ml-1) and analyzed immunohistochemically 3 days later. A heterogeneous pattern of Class II expression was present in the interferon-gamma-stimulated retinal pigment epithelial cells, in both the in vivo and the in vitro experiments. In aged human eyes the percent of Class-II positive cells was higher in the periphery than in the posterior pole (macular region) after interferon-gamma stimulation (P<0.01). No such difference was found in the fetal eyes. These data demonstrate that retinal pigment epithelial cells are heterogeneous in their response to interferon-gamma. The results are supportive of previous studies demonstrating the structural and proliferative heterogeneity of the retinal pigment epithelium. Together, these studies provide support for the possibility of functional retinal pigment epithelial heterogeneity.

Cellular response in subretinal neovascularization induced by bFGF-impregnated microspheres

PURPOSE

To determine the sequence of cellular changes associated with a new rabbit model of subretinal neovascularization (SRN) induced by subretinal injection of basic fibroblast growth factor (bFGF)-impregnated microspheres.

METHODS

bFGF-impregnated gelatin microspheres, prepared by forming a polyion complex between gelatin and bFGF, were subretinally implanted into rabbit eyes. The eyes were studied by immunochemistry at 3 days to 8 weeks after implantation. Antibodies to CD4, CD8, cytokeratin, CD31, glial fibrillary acidic protein (GFAP), and RAM11 were used.

RESULTS

Cytokeratin-positive retinal pigment epithelial (RPE) cells appeared on day 3 and continued to increase in number in the subretinal space throughout the growth of the SRN membrane, becoming the predominant cell type. Macrophages (RAM11-positive) appeared early, but most disappeared within 7 days. GFAP-positive Müller cells were evident early in the retina but migrated into the subretinal space after 7 days; the gliotic adhesion they formed between the retina and the SRN membrane was prominent at 8 weeks. CD31-positive endothelial cells were first evident at 14 days and formed neovascular channels that were still present for up to 8 weeks. CD4- and CD8-positive lymphocytes appeared in the early stages but were few in number.

CONCLUSIONS

SRN membranes are primarily composed of RPE cells and vascular endothelial cells. The membrane adheres to the retina by a gliotic band. The cellular components involved in the membrane of this model resemble those found in SRN membranes removed from patients with age-related macular degeneration.

Retrovirus-mediated gene transfer to photocoagulation-induced choroidal neovascular membranes

PURPOSE

To determine the feasibility of experimental gene transfer to laser-induced choroidal neovascular membrane (CNVM) in rats, with a retroviral vector containing the reporter construct beta-galactosidase (beta-gal).

METHODS

Laser photocoagulation was used to induce CNVM in rats. To ascertain the duration of beta-gal expression in the CNVM, 23 rats received 10 burns (75 microm, 100 mW, 0.1 seconds) in their right eyes, and beta-gal expression was examined from day 3 to 4 months. In addition, 14 pigmented rats were treated with 3 photocoagulation burns in their right eyes. beta-gal vector was injected into the vitreous or subretinal space 2 days later. On day 14, fluorescein angiography was performed to detect choroidal neovascularization. Then, beta-gal expression in each photocoagulation-induced CNVM was examined by observing the exposed fundus of the eyes stained with the beta-gal substrate X-Gal.

RESULTS

beta-gal expression was identified in the CNVM induced by photocoagulation from day 5 (16.2% +/- 6.8% of the lesions) to 4 months (3.7% +/- 2.4%). Histopathologic examination revealed beta-gal-transduced macrophages and spindle-shaped cells, which amounted to 1.12% +/- 0.58% (at 2 weeks) of the total cells in the CNVM. beta-gal expression was restricted to the CNVM, and there was no beta-gal transduction in surrounding normal retinochoroidal tissue. There was no correlation between choroidal neovascularization formation and beta-gal expression.

CONCLUSIONS

The feasibility of gene transduction targeted to the photocoagulation-induced CNVM was demonstrated using retroviral vectors. By transducing functional genes, this model could be useful for investigating the possibility of gene therapy to inhibit formation of the CNVM in age-related macular degeneration.

Rapid isolation of choriocapillary endothelial cells by Lycopersicon esculentum-coated Dynabeads

In vitro studies of choroidal endothelial cells may be critical for understanding the pathogenesis of neovascularization in age-related macular degeneration, since endothelial cells from different sites are highly heterogeneous in their morphology and behavior. Isolation of choroidal endothelial cells is complicated and labor intensive because of the small size of the choroid and the difficulty of excluding contaminating cells. We describe a rapid, simplified method for the isolation of bovine choroidal endothelial cells using microdissection followed by the use of superparamagnetic beads (Dynabeads) coated with the endothelial cell-specific lectin Lycopersicon esculentum, which selectively binds to fucose residues on the endothelial cell surface. Cells bound to beads are isolated using a magnetic particle concentrator. Isolated cells grew to confluence in a monolayer with a cobblestone morphology and were shown to be endothelial cells by their greater than 95% immunoreactivity to von Willebrand factor and phagocytosis of dil-acetylated LDL. Isolated cells grew as tubes in three-dimensional cultures. This method markedly reduces the time needed for pure culture of cells and makes the in vitro study of choroidal endothelial cells practical and reproducible.

Verapamil inhibits proliferation, migration and protein kinase C activity in human retinal pigment epithelial cells

The effects of three calcium channel blockers, verapamil, diltiazem and nifedipine, were examined on in vitro proliferation and migration of human retinal pigment epithelial cells. Human retinal pigment epithelial cells were seeded in Dulbecco's modified essential medium with 10% fetal bovine serum and different concentrations of the three calcium channel blockers. After 3 days of treatment, cell proliferation was determined by cell counting and by [3H]-thymidine uptake. Cell viability was determined with trypan blue exclusion. For determination of cell migration, retinal pigment epithelial cells were grown to confluence and then growth-inhibited with mitomycin C. After a 3 mm zone was denuded, the cells were treated with different concentrations of the calcium channel antagonists. After 24 hr, the cells that had migrated over the wound edge were counted. To determine the involvement of protein kinase C in the verapamil effect, its activity was measured in both verapamil-treated and untreated cells. Verapamil dose dependently inhibited serum-induced proliferation of retinal pigment epithelial cells, when measured by cell number (IC50 14.6 microM) or [3H]-thymidine incorporation (IC50 11.3 microM). At concentrations of 15 microM and below, there was no effect on cell viability, as determined by morphology and trypan blue exclusion. Diltiazem inhibited cell proliferation at a concentration of 100 microM; however, 100 microM nifedipine had no effect. Verapamil showed a significant inhibition of serum-induced migration in the range of 10 microM to 0.1 microM. The IC50 of the inhibition of retinal pigment epithelial cell proliferation and migration by verapamil is significantly higher than that seen for effects on calcium channel blockage. Eight micromolar verapamil reversibly inhibited total protein kinase-C activity in retinal pigment epithelial cells suggesting the possibility that the drug may act by inhibiting the protein kinase-C pathway. These data suggest the potential of the calcium channel blocker verapamil as a pharmacological modulator of disorders such as proliferative vitreoretinopathy in which there is increased retinal pigment epithelial cell proliferation and migration.

Scanning and transmission electron microscopic findings during RPE wound healing in vivo

OBJECTIVE

To examine the scanning (SEM) and transmission (TEM) electron microscopic features of an in vivo rabbit model of retinal pigment epithelial (RPE) wound healing.

METHODS

Hydraulic debridement of the RPE was performed in one eye of each of 35 pigmented rabbits using a pars plana vitrectomy approach. Five of the 35 eyes were examined by either SEM or TEM on each of the following postoperative days: 0, 2, 4, 7, 14, 28 and 56.

RESULTS

TEM revealed that hydraulic RPE debridement results in only focal damage to the RPE basement membrane portion of Bruch's membrane and that this damage is repaired by day 7 without ultrastructural sequelae. SEM and TEM disclosed that the RPE cells at the margin of the debrided bed become flattened and enlarged and evolve a cytoskeletal reorganization with altered apical-basal polarity consistent with the development of a migrating phenotype. This is followed by gradual restoration to a more normal stationary RPE phenotype after initial closure (reepithelialization) of the RPE defect on day 7. RPE hyperplasia also occurs and may contribute to this repair process. Tight junctions are re-established among the apical surfaces of monolayered and multilayered RPE cells by day 7, coinciding with the restoration of the blood outer retinal barrier.

CONCLUSION

Hydraulic debridement of the RPE in vivo is a useful investigational model that provides important insight into the pathogenesis of outer retinal disorders and their treatment with such techniques as submacular surgery or RPE transplantation.

Retrovirus-mediated gene transfer targeted to retinal photocoagulation sites

Diabetic retinopathy is a major cause of acquired blindness due to the development of retinal neovascularization and associated traction retinal detachment. It is commonly treated with retinal photocoagulation therapy; however, progression to blindness remains a significant problem. To determine the feasibility of adjunctive anti-angiogenic gene therapy, we evaluated the capability of retroviral vectors, which transfer exogenous genes only into dividing cells, to transfer and express a beta-galactosidase gene selectively into photocoagulation sites. Thirty-five rabbits received 30 retinal photocoagulation burns in the right eye followed 2 days later by beta-galactosidase (G1nBgSvNa) or control (G1XSvNa) vector injection into the subretinal space. Beta-galactosidase expression was observed in the photocoagulation sites from 5 days after vector administration (31.7+/-7.0%) to 12 weeks (6.7+/-3.4%). Immunohistochemical studies of the treated retinas using antibody Ber-MAC3 and anti-cytokeratin antibodies revealed that transduced cells were macrophages and retinal pigment epithelial cells. To determine feasibility in a primate, two monkeys received 10 laser burns in the macula superior to the fovea followed 2 days later by G1nBgSvNa vector. beta-galactosidase expression was found in photocoagulation sites and foveal retina was well preserved. We conclude that gene transfer to retinal photocoagulation sites provides stable expression of the transduced gene with relatively high efficiency. This feasibility study suggests the possibility of transferring genes encoding for anti-angiogenic factors into photocoagulation sites to improve the efficacy of laser photocoagulation therapy.

Ability of retroviral transduction to modify the angiogenic characteristics of RPE cells

BACKGROUND

Retinal pigment epithelial (RPE) cells play an important role in the modulation of ocular angiogenesis. Transduction of RPE cells with retroviral vectors bearing modulating genes can result in long-term transgene expression and may alter the angiogenic characteristics of RPE cells. This study was designed to determine whether changes in angiogenic characteristics of RPE cells result from transduction with retroviral vectors bearing modulating genes, using in vitro angiogenic assays, including analysis of endothelial proliferation and wound healing.

METHODS

Human RPE cells were transduced with retroviral vectors bearing either a urokinase-type plasminogen activator (u-PA) or a tissue-type plasminogen activator (t-PA) cDNA. Ten weeks after gene transfer, RPE cells transduced with the u-PA (u-PA-RPE cells) or the t-PA cDNA (t-PA-RPE cells), or untransduced (control) RPE cells, were cocultured with human umbilical vein endothelial cells (HUVECs) by contacting and non-contacting coculture methods. The effects of these cells on proliferation and in vitro "wound healing" of HUVECs were evaluated.

RESULTS

Over 18 weeks, u-PA-RPE cells released large amounts of biologically active u-PA (total amount, 50.2 +/- 9.7 ng/10(6) cells/24 h), while t-PA-RPE cells released large amounts of functional t-PA (15.4 +/- 3.2 ng/10(6) cells/24 h). Control RPE cells did not release any detectable t-PA or u-PA. In the proliferation assay, u-PA-RPE cells stimulated HUVEC proliferation in contacting cell cultures, but not in non-contacting cell cultures. In contrast, t-PA-RPE cells, normal RPE cells or exogenous u-PA had no effect on HUVEC proliferation. In the wound healing assay, u-PA-RPE cells in contacting coculture and exogenous u-PA stimulated wound healing of HUVECs, while non-contacting u-PA-RPE cells, t-PA-RPE cells and normal RPE cells had no effect on HUVEC wound healing. RPE cells transduced with u-PA secreted large amounts of u-PA for as long as 18 weeks, and these cells stimulate HUVEC proliferation and in vitro wound healing. As a result, the angiogenic characteristics of RPE cells can undergo long-term changes.

CONCLUSIONS

These results suggest that genetically modified RPE cells can be used to modulate ocular angiogenesis and may have potential for gene therapy of ocular diseases.

Ocular gene therapy: experimental studies and clinical possibilities

The Human Genome Project will identify, map and sequence all 50,000-100,000 human genes and will provide the tools to determine the genetic basis of both common and rare diseases. Understanding the genetic basis of human disease will allow for the development of highly specific drugs and for replacement of the altered gene through gene therapy. Gene therapy may also be used to introduce a new function into cells with resulting therapeutic benefit. Genes may be delivered into cells in vitro or in vivo utilizing viral or nonviral vectors. Viral vectors which have been used include retroviruses, adenoviruses, adeno-associated viruses and herpes viruses. Ocular disorders with the greatest potential for benefit of gene therapy at the current time include hereditary ocular diseases, including retinitis pigmentosa, tumors such as retinoblastoma or melanoma, and acquired proliferative and neovascular retinal disorders. We have demonstrated the feasibility of ocular gene therapy in a rabbit model of proliferative vitreoretinopathy, using retroviral vectors containing the herpes simplex virus thymidine kinase 'suicide' gene. Although in vivo transduction efficiency is low, the strong bystander effect results in prominent killing of proliferating cells in this model leading to inhibition of disease. In the future, gene therapy has the potential for the replacement of defective gene products or introduction of new gene products into ocular cells. The selection of appropriate target genes and cells will be critical, as will the development of a methodology for safe, targeted gene transfer.

Hypericin inhibits choroidal endothelial cell proliferation and cord formation in vitro

PURPOSE

To evaluate the effect of hypericin on bovine choroidal endothelial cell proliferation and cord formation and on protein kinase C activity.

METHODS

The effect of hypericin (0.1-5 microM) on bovine choroidal endothelial cell proliferation was determined by cell number counting and a 3H-thymidine uptake assay in media containing 1, 5 or 10% serum. For the cord formation assay, bovine choroidal endothelial cells were seeded on basement membrane matrix, and the lengths of the capillary-like structures (cords) formed were quantified by image analysis. The effect of hypericin on cord formation was evaluated in the presence of serum or vascular endothelial growth factor. The effect of hypericin on protein kinase C activity was also measured in the presence or absence of light.

RESULTS

Hypericin inhibited bovine choroidal endothelial cell proliferation in a dose-dependent manner in the presence of light but not in the dark. Serum dose-dependently masked the inhibition of DNA synthesis by hypericin. Cord formation by bovine choroidal endothelial cells was stimulated by serum or vascular endothelial growth factor and inhibited by hypericin in the presence of light. Protein kinase C activity was completely inhibited by hypericin in the presence of light but only mildly inhibited in the absence of light.

CONCLUSIONS

Hypericin inhibits bovine choroidal endothelial cell proliferation and cord formation and choroidal endothelial cell protein kinase C activity. These results suggest that hypericin should be further investigated in animal models for its potential to inhibit subretinal neovascularization.

Retrovirus-mediated transfer of the suicide gene into retinal pigment epithelial cells in vitro

PURPOSE

Human retinal pigment epithelial (HRPE) cells are a major cell component in proliferative vitreoretinopathy (PVR) membranes. We investigated the feasibility of killing HRPE cells by retroviral-mediated transfer of the herpes simplex virus-thymidine kinase (HSV-tk) gene, also known as the suicide gene, into HRPE cells followed by ganciclovir treatment, and to study the so-called bystander effect. Such a treatment plan might serve as a possible therapy for PVR.

METHODS

Transduction efficiency was determined using retroviral vectors encoding the beta-galactosidase reporter gene. To evaluate the efficacy of suicide gene therapy. HRPE cells were transduced with retroviral vectors encoding the HSV-tk gene (G1TkSvNa), with empty vectors or without vectors, and were treated with 5 micrograms/ml ganciclovir. Sensitivity of HSV-tk positive HRPE cells to various concentrations of ganciclovir was evaluated. To demonstrate the bystander effect, HSV-tk positive cells were cultured with HSV-tk negative cells at varying proportions.

RESULTS

Transduction efficiency in vitro was 15.1 +/- 4.8%. Cell growth was significantly inhibited after transduction with G1TkSvNa followed by ganciclovir treatment (P < 0.01). Ganciclovir showed dose- and time-dependent cytotoxicity only on HSV-tk positive cells. The concentration that resulted in 50% inhibited was 0.1 micrograms/ml. In terms of the bystander effect, after ganciclovir treatment the viability of co-cultured cells decreased with increasing populations of HSV-tk positive cells.

CONCLUSIONS

HRPE cells were successfully transduced with the HSV-tk gene via retroviral vectors and displayed a strong bystander effect after treatment with ganciclovir. These results suggest that retrovirus-mediated suicide gene therapy might be a feasible treatment strategy for PVR.

Lineage study of degenerating photoreceptor cells in the rd mouse retina

PURPOSE

A retroviral marker was used to label daughter cells arising from individual neuroblasts in the rd mouse retina, in order to investigate the hypothesis that a clonal relationship exists among degenerating photoreceptor cells.

METHODS

On the day of birth, a single injection of retrovirus with a lac Z (beta-galactosidase) reporter construct was injected into the retina in the vicinity of the subretinal space. Descendants of single neuroblasts were identified histochemically by examining the retinas at P14 (postnatal day 14). Light and electron microscopic studies were used to identify the retrovirally-induced marker beta-galactosidase using Bluo-gal dye. Double-labeling of degenerating cone cells was accomplished by taking 100 microns vibratome sections of retrovirally-injected eyes and using either FITC-PNA or HRP-PNA to visualize clusters of degenerating cones as well as Bluo-gal labeled clones of photoreceptor cells on the same tissue section.

RESULTS

A relatively large number of clones of primarily photoreceptor cells were observed in the peripheral retinas of both normal and rd mice. In a few cases in the rd, photoreceptor cells in a given clone consisted of both PNA- and Bluo-gal-labeled cells as well as of only Bluo-gal-labeled cells.

CONCLUSION

These results suggest that during the period of intense cell death in the rd retina, a single dying photoreceptor cell can be surrounded by photoreceptors (either rods or cones) from the same clone that appear morphologically normal without evidence of degeneration.

cis-Hydroxyproline inhibits proliferation, collagen synthesis, attachment, and migration of cultured bovine retinal pigment epithelial cells

PURPOSE

Proliferative vitreoretinopathy (PVR) is characterized by the proliferation and migration of retinal pigment epithelial (RPE) and other cells into the vitreous cavity. The PVR membrane formation also is associated with collagen production by RPE. The authors examined the effect of a proline analog, cis-hydroxyproline (CHP), on proliferation, collagen synthesis, attachment, and migration of bovine RPE in vitro.

METHODS

The effect of CHP on cell proliferation was determined as a function of dosage and days in culture by counting the cell numbers on days 3, 6, and 9. Collagen synthesis was determined by trichloroacetic acid precipitation of the radiolabeled samples before and after bacterial collagenase digestion. The attachment assay involved type I collagen or fibronectin substrates or both (2.5 micrograms/well). For migration experiments, RPE cells were removed from a defined area of a confluent culture, and migration was quantitated by counting the number of cells migrating into the denuded area over 30 hours.

RESULTS

The addition of CHP inhibited RPE proliferation in both a dose- and a time-dependent manner; collagen synthesis, attachment, and migration also were inhibited by CHP in a dose-dependent manner. When the culture plates were coated with collagen, < 100 micrograms/ml of CHP had no effect on cell attachment. Higher doses of CHP resulted in mild inhibition of attachment on collagen-coated plates. Simultaneous addition of L-proline to the cultures resulted in blockade of these inhibitory effects on proliferation, collagen synthesis, attachment, and migration.

CONCLUSIONS

The results show that RPE functions critical to the development of PVR are inhibited by CHP, suggesting the possibility that this drug may have potential clinical application.

Retrovirus-mediated suicide gene transduction in the vitreous cavity of the eye: feasibility in prevention of proliferative vitreoretinopathy

In proliferative vitreoretinopathy (PVR), retinal pigment epithelial cells, fibroblasts, or other proliferating cells form contractile membranes in the vitreous cavity of the eye, resulting in traction retinal detachment. Retroviral vector-mediated transfer is a suitable method to transduce the herpes simplex virus thymidine kinase (HSV-tk) gene into proliferating cells in PVR, allowing for the selective killing of these cells. To determine the potential of gene transduction in the environment of the vitreous cavity, we evaluated the effect of vitreous humor on retroviral vector-mediated gene transduction of rabbit dermal fibroblasts in vitro and studied in vivo transduction in rabbit experimental PVR with retroviral vector G1BgSvNa. In addition, we studied the bystander effect in vitro and in vivo in a rabbit model of PVR, with low percentages of HSV-tk-positive cells. Finally, we evaluated the efficacy of intravitreal administration of HSV-tk retroviral vector G1TkSvNa followed by ganciclovir (GCV) in the prevention of experimental PVR. Vitreous humor reduced gene transfer efficiency in vitro in a dose-dependent manner. LacZ expression was found in cells of preretinal or intravitreal membranes of animals of both in vivo and in vitro transduction groups; however, in vivo transduction resulted in a decreased number of transduced cells, with a relative transduction efficiency of approximately 2%. Transduction of HSV-tk was associated with a powerful bystander effect both in vitro and in vivo with significant effects even when HSV-tk-positive cells represented only 1% of the population. In vivo transduction with G1TkSvNa followed by GCV significantly inhibited the development of PVR (p < 0.05). These results suggest that retroviral vector-mediated transfer of HSV-tk into the proliferating cells in PVR may be feasible and may provide a novel therapeutic strategy for this disease.

Vitamin E succinate inhibits proliferation and migration of retinal pigment epithelial cells in vitro: therapeutic implication for proliferative vitreoretinopathy

BACKGROUND

Retinal pigment epithelial (RPE) cells play an important role in proliferative vitreoretinopathy (PVR). Vitamin E succinate is an ester form of a potent biological antioxidant, vitamin E, and has unique effects on various cells. We examined the effect of vitamin E succinate on proliferation and migration of cultured bovine RPE cells, since these are critical steps in the development of PVR.

METHODS

Bovine RPE cells were cultured in minimal essential medium (MEM) containing 10% fetal calf serum (MEM-10). Cells were incubated with MEM-10 containing 25 microM vitamin E, vitamin E succinate, butylated hydroxytoluene (BHT) or d-mannitol. Cell proliferation was assessed by counting cell numbers on days 2, 4 and 6. 3H-Thymidine uptake was also examined in RPE cells incubated with various forms of vitamin E-- vitamin E, vitamin E succinate, Trolox, gamma-tocopherol, vitamin E acetate, vitamin E phosphate, vitamin E nicotinate--or antioxidants-- BHT or d-mannitol (25 microM each). RPE cell migration was studied as follows: A small area (5 x 15 mm) of confluent cultured RPE cells was denuded using a straight razor blade and incubation was continued for 20 h with MEM-10 containing vitamin E, vitamin E succinate, gamma-tocopherol or BHT. The number of cells that migrated into the denuded area from the wound edge in each microscopic field (x20) was counted and expressed as a percentage of control (MEM-10 alone).

RESULTS

The antioxidants, vitamin E and BHT, stimulated RPE cell proliferation and 3H-thymidine incorporation compared with the control, while vitamin E succinate significantly inhibited both proliferation and 3H-thymidine uptake (IC50, 23 microM). Other forms of vitamin E or d-mannitol had no effect. Neither vitamin E nor BHT had a significant effect on RPE cell migration (108.2% and 112.6% of control, respectively), but vitamin E succinate inhibited migration (58.3%). Cell viability, assessed by the trypan blue dye exclusion test, was not impaired by a 3-day incubation with 50 microM of vitamin E succinate.

CONCLUSIONS

An ester form of a physiological antioxidant, vitamin E succinate, inhibits RPE cell proliferation and migration without causing cellular toxicity. These findings suggest its therapeutic potential for the pharmacological treatment of PVR.

Hypericin inhibits cell growth and induces apoptosis in retinal pigment epithelial cells: possible involvement of protein kinase C

Proliferative vitreoretinopathy (PVR) is characterized by the proliferation and migration of retinal pigment epithelial (RPE) cells in the vitreous cavity. The drug hypericin, which is already in clinical use as an antidepressant, has shown promise as an antiviral and antineoplastic agent. To investigate the therapeutic potential of hypericin in PVR, we incubated RPE cells in standard medium with various serum concentrations containing 0.5 to 5 microM hypericin. In some experiments we studied the effects of hypericin in conjunction with the RPE growth stimulating cytokine tumor necrosis factor alpha (TNF-alpha). Dose-dependent inhibition of RPE cell proliferation with IC50 values of 0.7 microM and 3.3 microM in 1% and 5% serum respectively, was found. Even in conjunction with TNF-alpha, hypericin inhibited RPE proliferation with an IC50 value of 1.5 microM. The drug inhibited PKC activity in cells treated with a 2.5 microM dose by 72% after 30 min and by 100% after 180 min. Finally, hypericin induced RPE cells to undergo apoptotic cell death, as shown by the presence of DNA laddering. These results suggest that hypericin may have potential as a therapeutic drug for PVR and that its antiproliferative and apoptotic effects on RPE cells in vitro are in part mediated by PKC.

Retinal pigment epithelial wound healing in vivo

OBJECTIVE

To develop an in vivo rabbit model of retinal pigment epithelial wound healing that preserves the overlying retina.

METHODS

Hydraulic débridement of the retinal pigment epithelium was performed in one eye of 35 pigmented rabbits by means of a pars plana vitrectomy approach. Five of the 35 eyes were examined by stereoscopic color fundus photography, fluorescein angiography, and light microscopy on each of the following postoperative days: 0, 2, 4, 7, 14, 28, and 56.

RESULTS

Retinal pigment epithelial débridement with this technique results in apical decapitation of the retinal pigment epithelial cells followed by subsequent hydraulic removal of the residual nucleus-containing basal cellular debris. The retinal pigment epithelium-denuded Bruch's membrane was resurfaced mostly by a monolayer of flattened, hypopigmented retinal pigment epithelial cells within 4 days after débridement. Progressive retinal pigment epithelial hyperplasia also occurred beginning between postoperative days 2 and 4.

CONCLUSIONS

Retinal pigment epithelial wound healing after hydraulic débridement occurs rapidly and in a manner initially consistent with sliding migration. Progressive retinal pigment epithelial hyperplasia also occurs and may contribute to this repair process. Further investigation of retinal pigment epithelial repair by means of this in vivo model may provide important insight into the pathogenesis and treatment of outer retinal disorders.

Inhibition of experimental proliferative vitreoretinopathy by retroviral vector-mediated transfer of suicide gene. Can proliferative vitreoretinopathy be a target of gene therapy?

PURPOSE

To determine the potential of somatic gene transfer as a treatment for proliferative vitreoretinopathy (PVR), experimental PVR was induced in rabbits by intraocular injection of fibroblasts bearing the herpes simplex virus thymidine kinase (HStk) gene. These transduced cells should be susceptible to cytotoxicity by exposure to ganciclovir (GCV).

MATERIALS AND METHODS

Rabbit fibroblasts were transduced with retroviral vectors bearing an HStk gene. Proliferative vitreoretinopathy was induced by injection of 5 x 10(4) normal or HStk gene-transduced fibroblasts (HStk fibroblasts) into rabbit eyes. Ganciclovir (100 micrograms per eye) or saline was injected into the vitreous on days 0 and 4. Experimental animals were divided into three groups: group A received HStk fibroblasts with GCV; group B, normal fibroblasts with GCV; group C, HStk fibroblasts with saline. Proliferative vitreoretinopathy also was induced in several other groups of eyes, some receiving GCV and different proportions of HStk fibroblasts to normal fibroblasts, others receiving only normal fibroblasts and GCV. The eyes were examined by indirect ophthalmoscopy on days 4, 7, 14, and 28, and PVR was classified into six stages (0-5).

RESULTS

Proliferative vitreoretinopathy was induced and progressed over time in each group. On day 28, PVR was most severe in animals in group B (average stage, 4.6) and group C (average stage, 4.4). Proliferative vitreoretinopathy was inhibited in group A (average stage, 1.0). The groups that received mixed injection of HStk fibroblasts and normal fibroblasts had intermediate PVR. Results of histologic study showed no apparent toxic or pathologic reaction in the retinochoroidal tissue of group A animals.

CONCLUSIONS

Severity of experimental PVR clearly was reduced by transfer of the HStk gene and administration of GCV. This inhibitory effect also was produced by a combination of 10% HStk fibroblasts and 90% normal fibroblasts, indicating a significant bystander effect. These data suggest the potential of somatic gene therapy for the treatment of PVR.

A new model of subretinal neovascularization in the rabbit

PURPOSE

To establish a new model of subretinal neovascularization (SRN) in the rabbit by implanting basic fibroblast growth factor (bFGF)-impregnated gelatin microspheres beneath the retina.

METHODS

Basic fibroblast growth factor-impregnated gelatin microspheres were prepared by forming a polyion complex between gelatin and bFGF. The microspheres, containing 2.5 micrograms of bFGF, were injected into the subretinal space of rabbit eyes (n = 29). Control eyes (n = 10) received bFGF-free gelatin microspheres. Eyes were followed up for 3 days to 8 weeks by ophthalmoscopy, photography, fluorescein angiography, light microscopy, and transmission electron microscopy.

RESULTS

Twenty of 24 experimental eyes (83%) showed fluorescein leakage from SRN 2 weeks after implantation of the bFGF-impregnated microspheres. This leakage continued for 2 to 6 more weeks. In striking contrast, control eyes showed no fluorescein leakage. Histologic examination revealed SRN in all the experimental eyes but in none of the control eyes.

CONCLUSIONS

Subretinal implantation of bFGF-impregnated gelatin microspheres induces reproducible SRN in the rabbit.

In vitro studies of human choroidal endothelial cells

Vascular endothelial cells play an important role in progression or healing of various retinal or choroidal diseases and they have a broad organ specificity. We have grown and studied human choroidal endothelial cells (CECs) cultured in a collagen gel, where they form tube-like structures. CECs were differentially isolated from choroidal tissues and cultured to near homogeneity. The cells were embedded in a type I collagen gel in 24-well culture dishes and incubated with M199 medium containing 10% fetal calf serum. Gels were observed using phase contrast microscopy and were evaluated histologically by light and electron microscopy. The CECs were strongly positive for factor VIII-related antigen and actively ingested diI-acetylated LDL, indicating their endothelial nature. Ultrastructural analysis of the tube-like structures revealed a central lumen surrounded by cells joined apically by junctions and showing prominent pinocytotic activity, fenestrations and basement membrane formation; these features are typical of CECs in vivo. This preparation should be a useful tool to study the development of physiology and pathology of choroidal endothelium.

Migration of retinal pigment epithelium cells in vitro is regulated by protein kinase C

The migration of retinal pigment epithelial (RPE) cells is an important step in various pathologic conditions, including subretinal neovascularization (SRN) and proliferative vitreoretinopathy (PVR). Therefore, elucidation of the mechanism of RPE migration may be useful in devising effective treatment for these disorders. Since protein kinase C (PKC) has been shown to regulate the migration of other cell types, we studied the effects of PKC agonists and antagonists on RPE migration. We used an in vitro wound healing model in which a small area of a confluent monolayer of bovine RPE cells was denuded with a razor blade. The cultures were subsequently incubated with agents known to stimulate [phorbol 12-myristate 13-acetate (PMA)] or inhibit (calphostin C, staurosporine) PKC. After 20 hr, migration was measured as the number of cells that had entered the denuded area. We also measured the translocation of PKC from the cytosol to the membrane in order to determine the activation or inhibition of PKC by PMA and calphostin C in the cells. The phorbol ester PMA stimulated migration by 41%, and calphostin C and staurosporine inhibited migration by 38% and 31%, respectively, in a medium supplemented with 10% serum. To determine the requirement for serum in this modulation, we also measured the effects of PMA and calphostin C on RPE migration in serum-free medium. Under these conditions, basal migration was greatly decreased, but PMA stimulated migration by 177% and calphostin C inhibited migration by 93%. Since PKC modulation is known to induce the proliferation of cells, we also tested the effects of these agents on growth-inhibited migration by pretreating the cells with the antiproliferative drug mitomycin C. We found that modulation of PKC under these conditions equally affected growth-inhibited and growth-dependent migration. Therefore, based on the increase in RPE migration induced by a PKC agonist, and the decrease in migration caused by PKC antagonists, it is suggested that PKC-mediated signal transduction plays a crucial role in RPE cell migration. This knowledge may be useful in devising effective treatments for SRN and PVR.

Effect of tecogalan sodium on angiogenesis in vitro by choroidal endothelial cells

PURPOSE

To examine the possible inhibitory effect of tecogalan sodium, derived from bacteria, on three important components of in vitro angiogenesis (endothelial proliferation, migration, and tube formation in a collagen gel) using bovine choroidal endothelial cells (CECs).

METHODS

The effects of tecogalan sodium (1, 5, 25, 125, and 250 micrograms/ml) on cultured CECs were examined when basic fibroblast growth factor (bFGF, 10 ng/ml), vascular endothelial growth factor (VEGF, 50 ng/ml), a combination of bFGF (10 ng/ml) and VEGF (50 ng/ml) (bFGF/VEGF) and 10% fetal calf serum (FCS) were used as angiogenic stimulants. For the proliferation assay, CECs were cultured and the cell numbers counted on days 1, 3, and 5. For migration assay, CECs were seeded in the upper half of a Boyden chamber while an angiogenic growth factor was loaded in the lower half. After 6 hours of incubation, cell migration was evaluated by counting the numbers of migrated cells per microscopic field on the lower side of the filter. For the tube-forming assay, CECs were seeded in a type I collagen gel, and the length of the tube-like structures (an indicator of angiogenesis) formed by CECs per microscopic field was quantified by image analysis. The effect of neutralizing antibody for bFGF also was tested in these three assays.

RESULTS

All tested angiogenic stimulants induced CEC proliferation. The stimulatory effect of bFGF and bFGF/VEGF was reduced by tecogalan sodium (IC50 for bFGF effect, 26.1 micrograms/ml). However, the effect of VEGF and of 10% FCS was not altered by low doses of tecogalan sodium (< 25 micrograms/ml). Chemotaxis of CECs was stimulated by bFGF alone and by bFGF/VEGF, and this effect was inhibited by tecogalan sodium (IC50 for bFGF, 3.2 micrograms/ml). Stimulation of chemotaxis by VEGF alone and by 10% FCS was not affected by tecogalan sodium in low doses but was inhibited by high doses. Tube formation was stimulated by administration of each of the factors. Stimulation of tube formation by bFGF and by bFGF/VEGF was inhibited by tecogalan sodium (IC50 for bFGF, 18.2 micrograms/ml). High doses of tecogalan sodium (125 and 250 micrograms/ml) also inhibited 10% FCS-induced proliferation, migration, and tube formation.

CONCLUSION

bFGF, VEGF, and a combination of bFGF and VEGF stimulated proliferation, migration, and tube formation by CECs in vitro. These stimulatory effects, but especially those of bFGF, were inhibited by tecogalan sodium. If tecogalan sodium can be shown to have a similar effect in vivo, it might have the potential for pharmacologic control of subretinal neovascularization.

Vessel formation by choroidal endothelial cells in vitro is modulated by retinal pigment epithelial cells

OBJECTIVE

To elucidate the mechanism of bovine choroidal endothelial (BCE) cell angiogenesis and, in particular, the role of retinal pigment epithelial (RPE) cells by use of an in vitro coculture assay system.

METHODS

The BCE cells were isolated from choroidal tissues and cultured. They were embedded in type I collagen gel and incubated. The gel-embedded BCE cells were then covered with a monolayer of RPE cells, pericytes, choroidal fibroblasts, or additional BCE cells on culture day 0 or day 14. The BCE cells in culture formed a meshwork of tubelike structures. The length of the tubelike structures (micrometers per field) was quantified by image analysis, as an indicator of angiogenesis. The effect of RPE cells on normal and growth-arrested BCE cell tube formation was evaluated in this assay system. The mechanism of RPE-induced angiogenesis was studied by parallel experiments with the use of neutralizing antibodies against specific growth factors (basic fibroblast growth factor, vascular endothelial growth factor, and transforming growth factor beta).

RESULTS

Ultrastructural analysis revealed that the tubelike structures had features typical of choroidal endothelial cells. Cocultures initiated on day 0 revealed that BCE cell angiogenesis was promoted by overlying RPE cells and, to a lesser extent, by pericytes, choroidal fibroblasts, and additional BCE cells when compared with BCE cells without covering cells. In cocultures initiated after BCE tube formation (day 14), there was inhibition of BCE angiogenesis by overlying RPE cells when compared with cultures without overlay or with an overlay of BCE cells. The RPE cells stimulated tube formation of growth-arrested BCE cells less effectively than did normal BCE cells. Neutralizing antibody for basic fibroblast growth factor and vascular endothelial growth factor, but not transforming growth factor beta, inhibited control and RPE-induced tube formation by BCE cells.

CONCLUSIONS

Overlying RPE cells stimulate the formation of tubelike structures by choroidal endothelial cells more effectively than do fibroblasts or pericytes but inhibit BCE tube formation in older cultures. The effect involves endothelial proliferation and differentiation. The stimulatory effect of overlying RPE cells can be inhibited by neutralizing antibodies to vascular endothelial growth factor and basic fibroblast growth factor, which suggests that these growth factors play an important role in this phenomenon.

beta-Galactosidase transgene expression in transplanted rabbit retinal pigment epithelial cells in vivo

BACKGROUND

Intraocular transplantation of genetically modified cells that release a particular substance could have a major impact on the treatment of various ocular diseases. We studied the expression of the reporter gene beta-galactosidase (lacZ) in transplanted retinal pigment epithelial (RPE) cells in vivo.

METHODS

RPE cells from pigmented rabbits were transduced with the beta-galactosidase gene in a retroviral vector. Cells were then assayed for gene expression and transplanted subretinally into the eyes of New Zealand White rabbits. RPE cells that were transduced with a similar vector without the beta-galactosidase gene were used as controls. Rabbits were killed on days 1, 7, and 21 and the eyes processed for transmission electron microscopy

RESULTS

Neomycin-resistant rabbit RPE cells that showed beta-galactosidase activity were generated within 2-5 weeks. After transplantation, viable RPE cells that expressed the transgene and that phagocytosed rod outer segments were observed on days 1, 7, and 21

CONCLUSIONS

The results show that generation of genetically modified RPE cells is feasible and that the transplanted cells remain viable and continue to express the transgene in the subretinal space of the host animal for at least 21 days. Transplantation of such genetically modified RPE cells could provide a new tool for studying retinal diseases and, potentially, for correcting metabolic abnormalities in retinal degenerations and dystrophies.

Effect of intravitreal administration of indomethacin on experimental subretinal neovascularization in the subhuman primate

OBJECTIVE

To examine the effect of indomethacin, a cyclooxygenase (CO) inhibitor, on laser-induced subretinal neovascularization (SRN) in the monkey. The CO pathway of arachidonic acid metabolism plays an important role in angiogenesis, and the inhibition of CO is known to inhibit angiogenesis in the cornea and in certain tumors.

MATERIALS AND METHODS

A cannula was implanted into the vitreous cavity of 11 eyes of six monkeys and connected to an osmotic minipump. Indomethacin (25 micrograms/d) was delivered into the vitreous through the cannula for 14 days (seven eyes). Vehicle alone was injected for 14 days as a control (four eyes). Argon laser photocoagulation was then performed (eight spots at the posterior pole in each eye) to induce SRN. Fundus photographs and fluorescein angiograms were taken periodically to document the evolution of SRN. Light and electron microscopic examination was performed on two eyes of each group 8 weeks after photocoagulation.

RESULTS

Subretinal neovascularization developed from 2 to 4 weeks after photocoagulation. The incidence of SRN, indicated by fluorescein leakage, was significantly lower (P < .05) in the group treated with indomethacin (14.3%, eight of 56 lesions) than in the control group (37.5%, 12 of 32 lesions). After 8 weeks, no fluorescein leakage was found in either the control or indomethacin-treated groups. Scar formation was found on histologic examination in both groups. No histologic evidence of indomethacin toxicity was seen in the adjacent retina.

CONCLUSIONS

Intravitreal administration of indomethacin inhibits the formation of laser-induced SRN in monkey eyes. This is consistent with the participation of the CO pathway in the process of SRN formation and suggests that this pathway could be a potential target in the treatment of SRN.

Inhibition of experimental proliferative vitreoretinopathy in rabbits by suramin

Proliferative vitreoretinopathy (PVR) is the most common cause for failure of retinal reattachment surgery. In a search for better pharmacologic treatment of PVR, we investigated the effect of intravenous injections of suramin on an experimental rabbit model of PVR. PVR was induced in rabbits by intravitreal injection of autologous fibroblasts. The experimental group (7 eyes) received intravenous injections of suramin (100 mg/kg body weight) every 3 days for 15 days, beginning 3 days before fibroblast injection. The control group (5 eyes) was treated similarly but received intravenous saline solution in place of suramin. A third group (4 eyes) received suramin according to the protocol above but did not receive intravitreal fibroblasts. The animals were examined by indirect ophthalmoscopy every 3 days and were sacrificed 14 days after the injection of fibroblasts. The serum levels of suramin were evaluated by high-performance liquid chromatography. The PVR was classified as stages I-V, based upon clinical findings. PVR developed in both experimental and control animals but was less severe in those treated with suramin. On day 14, the average stage of PVR in the control group was 3.8; in the suramin-treated group, however, the average stage was 2.4, which was significantly less than in the control group (p < 0.02). None of the rabbits in the third group showed pathologic changes. Serum levels of suramin were maintained at an average of 280.2 micrograms/ml and no apparent toxicity was found in the retina by histologic study.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytoplasmic retinal localization of an evolutionary homolog of the visual pigments

A rhodopsin-related protein is preferentially expressed at high levels in retinal pigment epithelium (RPE) and in Müller cells. The putative RPE-retinal G protein-coupled receptor (RGR) was localized in light-adapted bovine retina by means of electron microscopic immunocytochemistry. In the RPE, the protein was localized to a widespread intracellular compartment. Except for the region adjacent to the basal surface, the RPE cytoplasm was labeled throughout the cell including the apical surface. In Müller cells also RGR was found in the intracellular compartment, especially in the cytoplasm in the region of the Müller cell endfeet and proximal cell processes. Subcellular fractionation studies of bovine RPE and neural retina indicated that RGR is a membrane-bound protein. The intracellular localization of RGR is a unique variation in the subcellular distribution of seven-transmembrane-domain receptors and suggests an unconventional role for RGR in the signal transduction process.

Retinal degeneration in the pcd/pcd mutant mouse: accumulation of spherules in the interphotoreceptor space

The Purkinje cell degeneration (pcd) mutant mouse rapidly loses cerebellar Purkinje cells and about 50% of its retinal photoreceptor cells at between 3 and 5 weeks of age, and thereafter slowly loses the remaining photoreceptor cells during the first year of life. An ultrastructural study of the developing photoreceptor cells of the pcd/pcd retina was undertaken using both transmission and scanning electron microscopy to characterize further the previously reported retinal vesicles associated with this mutation. Transmission electron microscopy (TEM) revealed an abundance of 'bead-like' vesicles or excrescences in the extracellular matrix surrounding the inner segment region at post-natal day (P) 25. The vesicles are membrane bound, amorphous in appearance and vary in size from 125 to 370 nm. Scanning electron microscopy suggests that the vesicles seen with TEM are actually spherules formed from outpocketing and pinching off of the plasma membrane in the mitochondria-rich region of the rod inner segment. At P25, the spherules are concentrated in the interphotoreceptor space at the level of rod inner segments; at P40, however, they are displaced from their origin and appear mostly at the level of rod outer segments and in the subretinal space.

Ultrastructural visualization of primate cone photoreceptor matrix sheaths

Glycoconjugates, including glycolipids, glycoproteins, and proteoglycans, are present in the plasma membrane of photoreceptor cells and in the interphotoreceptor matrix surrounding photoreceptor cell ellipsoids and outer segments. Although the precise function of these molecules is unknown, they may be important in mediating photoreceptor-pigment epithelial cell interactions, outer segment membrane assembly, and/or disc shedding. Lectins, affinity ligands for defined carbohydrate sequences, have proven particularly useful in studying the glycoconjugate composition of the interphotoreceptor matrix. The peanut lectin selectively binds to domains of the interphotoreceptor matrix surrounding cone ("cone matrix sheaths"), but not rod inner and outer segments. This is evidence for the existence of chemical and structural heterogeneity within the interphotoreceptor matrix. The studies described herein utilized ultrastructural pre-embedding histochemical labeling to assess whether, in addition to the surrounding interphotoreceptor matrix, peanut lectin binding is associated directly with that plasma membrane of cone inner and outer segments. This study confirms that ferritin-conjugated peanut agglutinin binds to cone matrix sheaths, and, in addition, provides ultrastructural evidence for the presence of binding to the plasma membrane surrounding cone inner and outer segments. The data suggest that cone membrane-associated peanut agglutinin-binding molecules may differ from those located within cone matrix sheaths.