A comparison of different cellular inocula in an experimental model of massive periretinal proliferation

Myo/Nog Cells Give Rise to Myofibroblasts During Epiretinal Membrane Formation in a Mouse Model of Proliferative Vitreoretinopathy

Purpose

Myo/Nog cells are the source of myofibroblasts in the lens and synthesize muscle proteins in human epiretinal membranes (ERMs). In the current study, we examined the response of Myo/Nog cells during ERM formation in a mouse model of proliferative vitreoretinopathy (PVR).

Methods

PVR was induced by intravitreal injections of gas and ARPE-19 cells. PVR grade was scored by fundus imaging, optical coherence tomography, and histology. Double label immunofluorescence localization was performed to quantify Myo/Nog cells, myofibroblasts, and leukocytes.

Results

Myo/Nog cells, identified by co-labeling with antibodies to brain-specific angiogenesis inhibitor 1 (BAI1) and Noggin, increased throughout the eye with induction of PVR and disease progression. They were present on the inner surface of the retina in grades 1/2 PVR and were the largest subpopulation of cells in grades 3 to 6 ERMs. All α-SMA-positive (+) cells and all but one striated myosin+ cell expressed BAI1 in grades 1 to 6 PVR. Folds and areas of retinal detachment were overlain by Myo/Nog cells containing muscle proteins. Low numbers of CD18, CD68, and CD45+ leukocytes were detected throughout the eye. Small subpopulations of BAI1+ cells expressed leukocyte markers. ARPE-19 cells were found in the vitreous but were rare in ERMs. Pigmented cells lacking Myo/Nog and muscle cell markers were present in ERMs and abundant within the retina by grade 5/6.

Conclusions

Myo/Nog cells differentiate into myofibroblasts that appear to contract and produce retinal folds and detachment. Targeting BAI1 for Myo/Nog cell depletion may be a pharmacological approach to preventing and treating PVR.

Idelalisib inhibits experimental proliferative vitroretinopathy

Proliferative vitreoretinopathy (PVR) is a fibrotic eye disease that develops after rhegmatogenous retinal detachment surgery and open-globe traumatic injury. Idelalisib is a specific inhibitor of phosphoinositide 3-kinase (PI3K) δ. While PI3Kδ is primarily expressed in leukocytes, its expression is also considerably high in retinal pigment epithelial (RPE) cells, which play a crucial part in the PVR pathogenesis. Herein we show that GeoMx Digital Spatial Profiling uncovered strong expression of fibronectin in RPE cells within epiretinal membranes from patients with PVR, and that idelalisib (10 μM) inhibited Akt activation, fibronectin expression and collagen gel contraction induced by transforming growth factor (TGF)-β2 in human RPE cells. Furthermore, we discovered that idelalisib at a vitreal concentration of 10 μM, a non-toxic dose to the retina, prevented experimental PVR induced by intravitreally injected RPE cells in rabbits assessed by experienced ophthalmologists using an indirect ophthalmoscope plus a + 30 D fundus lens, electroretinography, optical coherence tomography and histological analysis. These data suggested idelalisib could be harnessed for preventing patients from PVR.

Intravitreal Tissue Plasminogen Activator Injection for the Treatment of Proliferative Vitreoretinopathy in a Rabbit Model

INTRODUCTION

The purpose of this study was to evaluate the effect of intravitreal injection of tissue plasminogen activator (tPA) on proliferative vitreoretinopathy (PVR).

METHODS

PVR was induced in a rabbit model by intraocular injection of dispase (0.05 U/0.1 mL). Progression of PVR was followed by indirect ophthalmic examination. Following 6 weeks, 5 animals received intravitreal injection of 25 µg/0.1 mL tPA and four were injected with balanced salt solution (BSS). Animals were euthanized at 48 h following tPA/BSS injection, and eyes were enucleated for histological evaluation and staining with α-smooth muscle actin (αSMA) and Sirius Red.

RESULTS

Following tPA injection, one eye had a reduction in PVR from grade 2 to 1 and three eyes remained stable. Following BSS, PVR grade was unchanged in three eyes. In one eye in each group, the severity of PVR could not be assessed due to limited view. Staining with αSMA showed reduced presence of fibroblasts in eyes injected with tPA compared with those injected with BSS. Collagen type I and III, demonstrated by Sirius Red staining, was reduced in the tPA group in comparison with controls.

CONCLUSION

Our results suggest that intravitreally injected tPA may show an inhibitory effect on PVR progression. Further exploration in clinical trials is desired.

Topical delivery of a small molecule RUNX1 transcription factor inhibitor for the treatment of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is the leading cause of retinal detachment surgery failure. Despite significant advances in vitreoretinal surgery, it still remains without an effective prophylactic or therapeutic medical treatment. After ocular injury or retinal detachment, misplaced retinal cells undergo epithelial to mesenchymal transition (EMT) to form contractile membranes within the eye. We identified Runt-related transcription factor 1 (RUNX1) as a gene highly expressed in surgically-removed human PVR specimens. RUNX1 upregulation was a hallmark of EMT in primary cultures derived from human PVR membranes (C-PVR). The inhibition of RUNX1 reduced proliferation of human C-PVR cells in vitro, and curbed growth of freshly isolated human PVR membranes in an explant assay. We formulated Ro5-3335, a lipophilic small molecule RUNX1 inhibitor, into a nanoemulsion that when administered topically curbed the progression of disease in a novel rabbit model of mild PVR developed using C-PVR cells. Mass spectrometry analysis detected 2.67 ng/mL of Ro5-3335 within the vitreous cavity after treatment. This work shows a critical role for RUNX1 in PVR and supports the feasibility of targeting RUNX1 within the eye for the treatment of an EMT-mediated condition using a topical ophthalmic agent.

Endogenous or Exogenous Retinal Pigment Epithelial Cells: A Comparison of Two Experimental Animal Models of Proliferative Vitreoretinopathy

Purpose

Proliferative vitreoretinopathy (PVR) is a blinding condition that can occur following ocular penetrating injury and retinal detachment. To develop effective therapeutics for PVR, it is imperative to establish an animal model that is reproducible, closest in anatomy to the human eye, and most representative of the human disease. We compared two in vivo models of PVR in minipig eyes to assess reproducibility and consistency.

Methods

Six minipigs underwent PVR induction with procedure A and six underwent procedure B. In both procedures, PVR was induced with vitrectomy, bleb retinal detachment, retinotomy, and injection of platelet-rich plasma. In procedure A, retinal pigment epithelial (RPE) cells were harvested from cadaveric pig eyes and injected at the end of surgery. In procedure B, native RPE cells were released into the vitreous cavity by creating a RPE detachment and scraping the RPE layer. PVR severity was graded on fundoscopic examination with a modified Silicone Study Classification System for PVR. Severe PVR was defined as stages 2 to 5.

Results

Three eyes (50%) and five eyes (83.3%) developed re-detachment of the retina from severe PVR in procedures A and B, respectively (P = 0.55). Median PVR stage was higher in eyes that underwent procedure B compared to eyes that underwent procedure A, although the difference was not statistically significant (2.5 vs. 1.5, P = 0.26).

Conclusions

This new model utilizing native RPE cells achieved a high consistency in inducing severe PVR in the minipig.

Translational Relevance

Our model closely follows pathogenic events in human PVR, making it ideal for preclinical testing of novel therapeutics for PVR.

A Mouse Model of Proliferative Vitreoretinopathy Induced by Intravitreal Injection of Gas and RPE Cells

Purpose

Develop a reproducible proliferative vitreoretinopathy (PVR) mouse model that mimics human PVR pathology.

Methods

Mice received intravitreal injections of SF6 gas, followed by retinal pigment epithelial cells 1 week later. PVR progression was monitored using fundus photography and optical coherence tomography imaging, and histologic analysis of the retina as an endpoint. We developed a PVR grading scheme tailored for this model.

Results

We report that mice that received gas before retinal pigment epithelial injection developed more severe PVR. In the 1 × 104 retinal pigment epithelial cell group, after 1 week, 0 of 11 mice in the no gas group developed grade 4 or greater PVR compared with 5 of 13 mice in the SF6 gas group (P = 0.02); after 4 weeks, 3 of 11 mice in the no gas group developed grade 5 or greater PVR compared with 11 of 14 mice in the SF6 gas group (P = 0.01). We were able to visualize contractile membranes both on the retinal surface as well as within the vitreous of PVR eyes, and demonstrated through immunohistochemical staining that these membranes expressed fibrotic markers alpha smooth muscle actin, vimentin, and fibronectin, as well as other markers known to be found in human PVR membranes.

Conclusions

This mouse PVR model is reproducible and mimics aspects of PVR pathology reported in the rabbit PVR model and human PVR. The major advantage is the ability to study PVR development in different genetic backgrounds to further elucidate aspects of PVR pathogenesis. Additionally, large-scale experiments for testing pharmacologic agents to treat and prevent PVR progression is more feasible compared with other animal models.

Translational Relevance

This model will provide a platform for screening potential drug therapies to treat and prevent PVR, as well as elucidate different molecular pathways involved in PVR pathogenesis.

GSK3β inhibits epithelial-mesenchymal transition via the Wnt/β-catenin and PI3K/Akt pathways

AIM

To investigate the regulatory mechanism of glycogen synthase kinase 3β (GSK3β) in epithelial-mesenchymal transition (EMT) process after proliferative vitreoretinopathy (PVR) induction.

METHODS

Experimental PVR was induced by intravitreal injection of retinal pigment epithelium (RPE) cells in the eyes of rabbits. A PI3K/Akt inhibitor (wortmannin) and a GSK3β inhibitor (LiCl) were also injected at different time during PVR progress. Electroretinogram (ERG), ocular fundus photographs, and B-scan ultrasonography were used to observe the PVR progress. Western blot test on the extracted retina were performed at 1, 2, 4wk. The expression of the mesenchymal marker vimentin was determined by immunohistochemistry. Toxicity of wortmannin and LiCl were evaluated by ERG and TdT-mediated dUTP nick-end labeling (TUNEL) assay. The vitreous was also collected for metabolomic analysis.

RESULTS

Experimental PVR could significantly lead to EMT, along with the suppressed expression of GSK3β and the activation of Wnt/β-catenin and PI3K/Akt pathways. It was verified that upregulating the expression of GSK3β could effectively inhibit EMT process by suppressing Wnt/β-catenin and PI3K/Akt pathways.

CONCLUSION

GSK3β effectively inhibits EMT via the Wnt/β-catenin and PI3K/Akt pathways. GSK3β may be regarded as a promising target of experimental PVR inhibition.

Experimental proliferative vitreoretinopathy in rabbits by delivery of bioactive proteins with gelatin microspheres

Proliferative vitreoretinopathy (PVR) is a challenging pathological condition, often causing failure of retinal detachment surgery. The purpose of this study was to evaluate the feasibility of a delivery system of bioactive proteins using anionic and cationic gelatin microspheres and to establish a new PVR model in rabbits by intraocular sustained delivery of basic fibroblast growth factor (bFGF) and interferon-beta (IFNβ). Anionic and cationic gelatin microspheres were prepared and immersed in bFGF and IFNβ solution, respectively, to yield a polyion complex between gelatin matrix and a bioactive protein. The bFGF-impregnated microspheres were injected into the subretinal space in rabbit eyes. At week 2, the IFNβ-impregnated microspheres also were injected into the same space. Control eyes received gelatin microspheres without bFGF or IFNß, or both. The eyes then were observed for 8 weeks by ophthalmoscopy, fundus photography, and fluorescein angiography. The eyes also were evaluated histologically. In the group with both bFGF and IFNβ, the number of eyes with more severe PVR increased over time. Histologic examination showed retinal folds. In contrast, no proliferative changes were seen in any control groups. Subretinal implantation of bFGF and IFNβ-impregnated gelatin microspheres induced reproducible PVR in rabbit eyes. This study guaranteed delivery of bioactive proteins with gelatin microspheres.

Introduction of the MDM2 T309G Mutation in Primary Human Retinal Epithelial Cells Enhances Experimental Proliferative Vitreoretinopathy

Purpose

The murine double minute (MDM)2 is a critical negative regulator of the p53 tumor suppressor, and MDM2 SNP309G is associated with a higher risk of proliferative vitreoretinopathy (PVR); in addition, the MDM2 T309G created using clustered regularly interspaced short palindromic repeats (CRISPR)/associated endonuclease (Cas)9 enhances normal rabbit vitreous-induced expression of MDM2 and survival of primary human retinal pigment epithelial (hRPE) cells in vitro. The goal of this study was to determine whether this MDM2 T309G contributes to the development of experimental PVR.

Methods

hRPE cells expressing MDM2 T309G or T309T only were treated with vitreous from human PVR donors (HV). The expression of MDM2 and p53 in the treated cells was examined by Western blot. The in vitro vitreous-induced cellular responses, such as contraction were assessed, and PVR was induced by intravitreal injection of the hRPE cells with MDM2 T309G or T309T only into rabbit eyes.

Results

Western blot analyses indicated that treatment of hRPE cells with HV led to a significant increase (1.7 ± 0.2-fold) in the expression of MDM2 and a significant decrease in p53 in the cells expressing MDM2 T309G compared with those with MDM2 T309T. In addition, HV promoted contraction of the hRPE cells expressing MDM2 T309G significantly more than those with MDM2 T309T only. Furthermore, MDM2 T309G in the hRPE cells enhanced the development of PVR in a rabbit model.

Conclusions

The MDM2 SNP309 in RPE cells enhances their potential of PVR pathogenesis.

Prevention of Proliferative Vitreoretinopathy by Suppression of Phosphatidylinositol 5-Phosphate 4-Kinases

Purpose

Previous studies have shown that vitreous stimulates degradation of the tumor suppressor protein p53 and that knockdown of phosphatidylinositol 5-phosphate 4-kinases (PI5P4Kα and -β) abrogates proliferation of p53-deficient cells. The purpose of this study was to determine whether vitreous stimulated expression of PI5P4Kα and -β and whether suppression of PI5P4Kα and -β would inhibit vitreous-induced cellular responses and experimental proliferative vitreoretinopathy (PVR).

Methods

PI5P4Kα and -β encoded by PIP4K2A and 2B, respectively, in human ARPE-19 cells were knocked down by stably expressing short hairpin (sh)RNA directed at human PIP4K2A and -2B. In addition, we rescued expression of PI5P4Kα and -β by re-expressing mouse PIP4K2A and -2B in the PI5P4Kα and -β knocked-down ARPE-19 cells. Expression of PI5P4Kα and -β was determined by Western blot and immunofluorescence. The following cellular responses were monitored: cell proliferation, survival, migration, and contraction. Moreover, the cell potential of inducing PVR was examined in a rabbit model of PVR effected by intravitreal cell injection.

Results

We found that vitreous enhanced expression of PI5P4Kα and -β in RPE cells and that knocking down PI5P4Kα and -β abrogated vitreous-stimulated cell proliferation, survival, migration, and contraction. Re-expression of mouse PIP4Kα and -β in the human PI5P4Kα and -β knocked-down cells recovered the loss of vitreous-induced cell contraction. Importantly, suppression of PI5P4Kα and -β abrogated the pathogenesis of PVR induced by intravitreal cell injection in rabbits. Moreover, we revealed that expression of PI5P4Kα and -β was abundant in epiretinal membranes from PVR grade C patients.

Conclusions

The findings from this study indicate that PI5P4Kα and -β could be novel therapeutic targets for the treatment of PVR.

Pirfenidone inhibits post-traumatic proliferative vitreoretinopathy

PurposeThe purpose of the study was to evaluate the efficacy and safety of intravitreal pirfenidone for inhibition of proliferative vitreoretinopathy (PVR) in a model of penetrating ocular injury.Patients and methodsPenetrating trauma was induced on the retina of rabbit and treated either with 0.1 ml of phosphate-buffered saline (PBS) or 0.1 ml of 0.5% pirfenidone, and development of PVR was evaluated clinically and graded after 1 month. Histopathology and immunohistochemistry with transforming growth factor beta (TGFβ), alpha smooth muscle actin (αSMA), and collagen-1 were performed to assess the fibrotic changes. Expression of cytokines in the vitro-retinal tissues at different time points following pirfenidone and PBS injection was examined by RT-PCR. Availability of pirfenidone in the vitreous of rabbit at various time points was determined by high-performance liquid chromatography following injection of 0.1 ml of 0.5% pirfenidone. In normal rabbit eye, 0.1 ml of 0.5% pirfenidone was injected to evaluate any toxic effect.ResultsClinical assessment and grading revealed prevention of PVR formation in pirfenidone-treated animals, gross histology, and histopathology confirmed the observation. Immunohistochemistry showed prevention in the expression of collagen-I, αSMA, and TGFβ in the pirfenidone-treated eyes compared to the PBS-treated eyes. Pirfenidone inhibited increased gene expression of cytokines observed in control eyes. Pirfenidone could be detected up to 48 h in the vitreous of rabbit eye following single intravitreal injection. Pirfenidone did not show any adverse effect following intravitreal injection; eyes were devoid of any abnormal clinical sign, intraocular pressure, and electroretinography did not show any significant change and histology of retina remained unchanged.ConclusionThis animal study shows that pirfenidone might be a potential therapy for PVR. Further clinical study will be useful to evaluate the clinical application of pirfenidone.

Histopathological and ophthalmoscopic evaluation of apocynin on experimental proliferative vitreoretinopathy in rabbit eyes

The aim of the current study was to evaluate the effect of apocynin (APO) on the development of proliferative vitreoretinopathy (PVR). New Zealand-type male rabbits were randomly grouped into three as follows: (1) Sham group rabbits which were applied intraperitoneal (i.p.) vehicle without PVR; (2) PVR group rabbits where PVR was created and an i.p. vehicle was administered for 21 successive days; (3) PVR + APO group rabbits where PVR was created and i.p. APO was administered for 21 successive days. Fundus examination was conducted with an indirect ophthalmoscope before starting the experiments and at each visit afterwards. At the end of the work, the rabbits were sacrificed under high-dose anesthesia and then eye tissues were taken for histopathological analyses. In the PVR + APO group, histopathologic and ophthalmoscopic examination revealed significant decrease in PVR formation. As the result, it has been observed that APO at least partially inhibits PVR formation.

Proliferative vitreoretinopathy: A new concept of disease pathogenesis and practical consequences

During the last four decades, proliferative vitreoretinopathy (PVR) has defied the efforts of many researchers to prevent its occurrence or development. Thus, PVR is still the major complication following retinal detachment (RD) surgery and a bottle-neck for advances in cell therapy that require intraocular surgery. In this review we tried to combine basic and clinical knowledge, as an example of translational research, providing new and practical information for clinicians. PVR was defined as the proliferation of cells after RD. This idea was used for classifying PVR and also for designing experimental models used for testing many drugs, none of which were successful in humans. We summarize current information regarding the pathogenic events that follow any RD because this information may be the key for understanding and treating the earliest stages of PVR. A major focus is made on the intraretinal changes derived mainly from retinal glial cell reactivity. These responses can lead to intraretinal PVR, an entity that has not been clearly recognized. Inflammation is one of the major components of PVR, and we describe new genetic biomarkers that have the potential to predict its development. New treatment approaches are analyzed, especially those directed towards neuroprotection, which can also be useful for preventing visual loss after any RD. We also summarize the results of different surgical techniques and clinical information that is oriented toward the identification of high risk patients. Finally, we provide some recommendations for future classification of PVR and for designing comparable protocols for testing new drugs or techniques.

RasGAP Promotes Autophagy and Thereby Suppresses Platelet-Derived Growth Factor Receptor-Mediated Signaling Events, Cellular Responses, and Pathology

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) make profound contributions to both physiology and pathology. While it is widely believed that direct (PDGF-mediated) activation is the primary mode of activating PDGFRs, the discovery that they can also be activated indirectly begs the question of the relevance of the indirect mode of activating PDGFRs. In the context of a blinding eye disease, indirect activation of PDGFRα results in persistent signaling, which suppresses the level of p53 and thereby promotes viability of cells that drive pathogenesis. Under the same conditions, PDGFRβ fails to undergo indirect activation. In this paper, we report that RasGAP (GTPase-activating protein of Ras) prevented indirect activation of PDGFRβ. RasGAP, which associates with PDGFRβ but not PDGFRα, reduced the level of mitochondrion-derived reactive oxygen species, which are required for enduring activation of PDGFRs. Furthermore, preventing PDGFRβ from associating with RasGAP allowed it to signal enduringly and drive pathogenesis of a blinding eye disease. These results indicate a previously unappreciated role of RasGAP in antagonizing indirect activation of PDGFRβ, define the underlying mechanism, and raise the possibility that PDGFRβ-mediated diseases involve indirect activation of PDGFRβ.

Vascular endothelial growth factor acts primarily via platelet-derived growth factor receptor α to promote proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a nonneovascular blinding disease and the leading cause for failure in surgical repair of rhegmatogenous retinal detachments. Once formed, PVR is difficult to treat. Hence, there is an acute interest in developing approaches to prevent PVR. Of the many growth factors and cytokines that accumulate in vitreous as PVR develops, neutralizing vascular endothelial growth factor (VEGF) A has recently been found to prevent PVR in at least one animal model. The goal of this study was to test if Food and Drug Administration-approved agents could protect the eye from PVR in multiple animal models and to further investigate the underlying mechanisms. Neutralizing VEGF with aflibercept (VEGF Trap-Eye) safely and effectively protected rabbits from PVR in multiple models of disease. Furthermore, aflibercept reduced the bioactivity of both experimental and clinical PVR vitreous. Finally, although VEGF could promote some PVR-associated cellular responses via VEGF receptors expressed on the retinal pigment epithelial cells that drive this disease, VEGF's major contribution to vitreal bioactivity occurred via platelet-derived growth factor receptor α. Thus, VEGF promotes PVR by a noncanonical ability to engage platelet-derived growth factor receptor α. These findings indicate that VEGF contributes to nonangiogenic diseases and that anti-VEGF-based therapies may be effective on a wider spectrum of diseases than previously appreciated.

Is neutralizing vitreal growth factors a viable strategy to prevent proliferative vitreoretinopathy?

Proliferative vitreoretinopathy (PVR) is a blinding disorder that occurs in eyes with rhegmatogenous retinal detachment and in eyes that have recently undergone retinal detachment surgery. There are presently no treatment strategies to reduce the risk of developing PVR in eyes with retinal detachment, and surgical intervention is the only option for eyes with retinal detachment and established PVR. Given the poor visual outcome associated with the surgical treatment of PVR, considerable work has been done to identify pharmacologic agents that could antagonize the PVR process. Intensive efforts to identify molecular determinants of PVR implicate vitreal growth factors. A surprise that emerged in the course of testing the 'growth factor hypothesis' of PVR was the existence of a functional relationship amongst growth factors that engage platelet-derived growth factor (PDGF) receptor α (PDGFRα), a receptor tyrosine kinase that is key to pathogenesis of experimental PVR. Vascular endothelial cell growth factor A (VEGF), which is best known for its ability to activate VEGF receptors (VEGFRs) and induce permeability and/or angiogenesis, enables activation of PDGFRα by a wide spectrum of vitreal growth factors outside of the PDGF family (non-PDGFs) in a way that triggers signaling events that potently enhance the viability of cells displaced into vitreous. Targeting these growth factors or signaling events effectively neutralizes the bioactivity of PVR vitreous and prevents PVR in a number of preclinical models. In this review, we discuss recent conceptual advances in understanding the role of growth factors in PVR, and consider the tangible treatment strategies for clinical application.

Ranibizumab is a potential prophylaxis for proliferative vitreoretinopathy, a nonangiogenic blinding disease

Proliferative vitreoretinopathy (PVR) exemplifies a disease that is difficult to predict, lacks effective treatment options, and substantially reduces the quality of life of an individual. Surgery to correct a rhegmatogenous retinal detachment fails primarily because of PVR. Likely mediators of PVR are growth factors in vitreous, which stimulate cells within and behind the retina as an inevitable consequence of a breached retina. Three classes of growth factors [vascular endothelial growth factor A (VEGF-A), platelet-derived growth factors (PDGFs), and non-PDGFs (growth factors outside of the PDGF family)] are relevant to PVR pathogenesis because they act on PDGF receptor α, which is required for experimental PVR and is associated with this disease in humans. We discovered that ranibizumab (a clinically approved agent that neutralizes VEGF-A) reduced the bioactivity of vitreous from patients and experimental animals with PVR, and protected rabbits from developing disease. The apparent mechanism of ranibizumab action involved derepressing PDGFs, which, at the concentrations present in PVR vitreous, inhibited non-PDGF-mediated activation of PDGF receptor α. These preclinical findings suggest that available approaches to neutralize VEGF-A are prophylactic for PVR, and that anti-VEGF-based therapies may be effective for managing more than angiogenesis- and edema-driven pathological conditions.

A novel function of p53: a gatekeeper of retinal detachment

Proliferative vitreoretinopathy (PVR) is a blinding disease associated with rhegmatogenous retinal detachment, for which there is no satisfactory treatment. Surgery helps in many cases, but, to our knowledge, there are no pharmacological approaches to reduce PVR risk. We report that suppressing expression of p53 was a required event in two assays of PVR (namely, platelet-derived growth factor receptor α-mediated contraction of cells in a collagen gel and retinal detachment in an animal model of PVR). Furthermore, preventing the decline in the level of p53 with agents such as Nutlin-3 protected from retinal detachment, which is the most vision-compromising component of PVR. Finally, Nutlin-3 may be effective in the clinical setting because it prevented human PVR vitreous-induced contraction of cells isolated from a patient PVR membrane. These studies identify Nutlin-3 as a potential PVR prophylaxis.

A novel strategy to develop therapeutic approaches to prevent proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) thwarts the repair of rhegmatogenous retinal detachments. Currently, there is no effective prevention for PVR. Platelet-derived growth factor receptor α (PDGFRα) is associated with PVR in humans and strongly promotes experimental PVR driven by multiple vitreal growth factors outside the PDGF family. We sought to identify vitreal factors required for experimental PVR and to establish a potential approach to prevent PVR. Vitreous was obtained from normal rabbits or those in which PVR was either developing or stabilized. Normal vitreous contained substantial levels of growth factors and cytokines, which changed quantitatively and/or qualitatively as PVR progressed and stabilized. Neutralizing a subset of these agents in rabbit vitreous eliminated their ability to induce PVR-relevant signaling and cellular responses. A single intravitreal injection of neutralizing reagents for this subset prevented experimental PVR. To identify growth factors and cytokines likely driving PVR in humans, we subjected vitreous from patients with or without PVR to a similar series of analyses. This analysis accurately identified those agents required for vitreous-induced contraction of cells from a patient PVR membrane. We conclude that combination therapy encompassing a subset of vitreal growth factors and cytokines is a potential approach to prevent PVR.

The novel use of decorin in prevention of the development of proliferative vitreoretinopathy (PVR)

BACKGROUND

The cytokine transforming growth factor-ß (TGF-ß) is a pivotal contributor to tissue fibrosis and a key cytokine in the pathogenesis of cellular transdifferentiation, epithelial-mesenchymal transition (EMT), and cell adhesion. This study evaluates the effect of decorin, a naturally occurring TGF-ß inhibitor, in an experimental rabbit model for proliferative vitreoretinopathy (PVR).

METHODS

Traumatic PVR was induced in 50 rabbits divided into ten groups (n = 5). One group (GI) reveals a control with no treatment after trauma. Groups (GII-GIV) consisted of subgroups receiving phacovitrectomy at three different time points; (a) at the time of trauma, (b) 1 week following trauma, and (c) 2 weeks following trauma. GIII and GIV received 100 μg or 200 μg decorin, respectively. PVR severity was scored from 0 to 4. The amount of fibrosis was quantified using JMicroVision© software.

RESULTS

The control group GI developed severe PVR with tractional retinal detachment (TRD); (PVR score ≥2) in four rabbits out of five. Vitrectomy had a positive effect (p < 0.05) on PVR development when preformed immediately, however the developed fibrosis was high. The best results were obtained when surgery was used in conjunction with decorin that reduced both the PVR score and fibrosis development significantly (p < 0.05). Depending on dosage and time of vitrectomy, PVR could be completely avoided (PVR score = 0) in 16 rabbits out of 30. TRD was prevented in 13 rabbits out of 15 in GIII to 14 rabbits out of 15 in GIV. In decorin-treated eyes, vitrectomy outcome was best when preformed at 1 week after trauma. There were no drug-related toxic effects evident on clinical and histopathological examination.

CONCLUSIONS

In conclusion, in this rabbit model of PVR, adjuvant decorin application during vitrectomy effectively reduces fibrosis and TRD development. In conjunction with no obvious histopathological toxicity signs, decorin represents a promising substance to inhibit PVR reactions.

Pathological signaling via platelet-derived growth factor receptor {alpha} involves chronic activation of Akt and suppression of p53

In contrast to direct activation of platelet-derived growth factor (PDGF) receptor α (PDGFRα) via PDGF, indirect activation via growth factors outside the PDGF family failed to induce dimerization, internalization, and degradation of PDGFRα. Chronically activated, monomeric PDGFRα induced prolonged activation of Akt and suppressed the level of p53. These events were sufficient to promote both cellular responses (proliferation, survival, and contraction) that are intrinsic to proliferative vitreoretinopathy (PVR) and induce the disease itself. This signature signaling pathway appeared to extend beyond PVR since deregulating PDGFRα in ways that promote solid tumors also resulted in chronic activation of Akt and a decline in the level of p53.

N-acetylcysteine suppresses retinal detachment in an experimental model of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a complication that develops in 5% to 10% of patients who undergo surgery to correct a detached retina. The only treatment option for PVR is surgical intervention, which has a limited success rate that diminishes in patients with recurring PVR. Our recent studies revealed that antioxidants prevented intracellular signaling events that were essential for experimental PVR. The purpose of this study was to test whether N-acetyl-cysteine (NAC), an antioxidant used in a variety of clinical settings, was capable of protecting rabbits from PVR. Vitreous-driven activation of PDGFRalpha and cellular responses intrinsic to PVR (contraction of collagen gels and cell proliferation) were blocked by concentrations of NAC that were well below the maximum tolerated dose. Furthermore, intravitreal injection of NAC effectively protected rabbits from developing retinal detachment, which is the sight-robbing phase of PVR. Finally, these observations with an animal model appear relevant to clinical PVR because NAC prevented human PVR vitreous-induced contraction of primary RPE cells derived from a human PVR membrane. Our observations demonstrate that antioxidants significantly inhibited experimental PVR, and suggest that antioxidants have the potential to function as a PVR prophylactic in patients undergoing retinal surgery to repair a detached retina.

Growth factors outside the PDGF family drive experimental PVR

PURPOSE

Proliferative vitreoretinopathy (PVR) is a recurring and problematic disease for which there is no pharmacologic treatment. Platelet-derived growth factor (PDGF) in the vitreous is associated with experimental and clinical PVR. Furthermore, PDGF receptors (PDGFRs) are present and activated in epiretinal membranes of patient donors, and they are essential for experimental PVR. These observations suggest that PVR arises at least in part from PDGF/PDGFR-driven events. The goal of this study was to determine whether PDGFs were a potential therapeutic target for PVR.

METHODS

Experimental PVR was induced in rabbits by injecting fibroblasts. Vitreous specimens were collected from experimental rabbits or from patients undergoing vitrectomy to repair retinal detachment. A neutralizing PDGF antibody and a PDGF Trap were tested for their ability to prevent experimental PVR. Activation of PDGFR was monitored by antiphosphotyrosine Western blot analysis of immunoprecipitated PDGFRs. Contraction of collagen gels was monitored in vitro.

RESULTS

Neutralizing vitreal PDGFs did not effectively attenuate PVR, even though the reagents used potently blocked PDGF-dependent activation of the PDGF alpha receptor (PDGFRalpha). Vitreal growth factors outside the PDGF family modestly activated PDGFRalpha and appeared to do so without engaging the ligand-binding domain of PDGFRalpha. This indirect route to activate PDGFRalpha had profound functional consequences. It promoted the contraction of collagen gels and appeared sufficient to drive experimental PVR.

CONCLUSIONS

Although PDGF appears to be a poor therapeutic target, PDGFRalpha is particularly attractive because it can be activated by a much larger spectrum of vitreal growth factors than previously appreciated.

siRNA targeting mammalian target of rapamycin (mTOR) attenuates experimental proliferative vitreoretinopathy

PURPOSE

To investigate the effect of mammalian target of rapamycin (mTOR) specific siRNA on proliferative vitreoretinopathy (PVR).

METHODS

Cultured human retinal pigment epithelial (hRPE) cell line D407 was treated with three mTOR specific small interfering RNAs. Cell proliferation, attachment, spreading, and migration were performed. The impact of the mTOR specific siRNA on PVR was tested using a rabbit model in which PVR was induced by the injection of hRPE cells.

RESULTS

Decreasing mTOR expression by about 82% using small interfering RNA resulted in a significant decrease in cell spreading and migration. Whereas retinal detachment occurred in 100% of the control group animals, co-injection of the mTOR specific siRNA substantially reduced the severity and incidence (50%) of retinal detachments.

CONCLUSIONS

Gene therapy with mTOR specific siRNA attenuates PVR in a rabbit model of the disease. This may be a new approach to preventing PVR in humans.

In vivo models of proliferative vitreoretinopathy

We outline current in vitro and in vivo models for experimental proliferative vitreoretinopathy (PVR) and provide a detailed protocol of our standardized in vivo PVR model. PVR is the leading cause of failed surgical procedures for the correction of rhegmatogenous retinal detachment. The pathogenesis of this multifactorial condition is still not completely understood. Experimental models for PVR help us understand the factors that play a role in the pathogenesis of the disease process in a controlled manner and allow for reproducible preclinical assessment of novel therapeutic interventions. We describe a cell injection model in detail that uses homologous retinal pigment epithelial (RPE) cell cultures to induce PVR over a 2-8 week period.

Effects of Topoisomerase II Inhibitors on Retinal Pigment Epithelium And Experimental Proliferative Vitreoretinopathy

AIMS

The aim of this study was to compare the effect of several commercially available topoisomerase II inhibitors on the proliferation of retinal pigment epithelium (RPE) cells in vitro and to test the toxicity and efficacy of the inhibitor against experimental proliferative vitreoretinopathy (PVR).

METHODS

Three different topoisomerase II inhibitors (etoposide, doxorubicin, and daunorubicin) were tested in vitro. Rabbit RPE cells were cultured with or without the drugs at various concentrations. An MTT assay was used to determine the cell viability at 48 h and 96 h. Etoposide, a drug which showed a broad therapeutic range in vitro, was injected to the rabbit eye for the evaluation of the toxicity in vivo. Therapeutic effects of an intravitreal injection of etoposide were evaluated in an experimental PVR model induced by the intravitreal implantation of RPE cells in rabbits.

RESULTS

All tested topoisomerase II inhibitors showed a significant reduction of cell viability in vitro. The slope of the dose-response curve was slowly declined for etoposide, and declined sharply for doxorubicin and daunorubicin. Therefore, etoposide was selected for further toxicity and efficacy studies in vivo. There was no significant change in b-wave amplitudes in the etoposide-injected eyes (0.02 mg, 10 microg/mL) after 2 weeks, but a significant reduction occurred in the etoposide-injected eyes (0.2 mg, 100 microg/mL). In the study of the experimental model of PVR, the rabbit eyes injected with RPE cells and etoposide (0.02 mg, 10 microg/mL) showed a significantly lower grading of PVR than that of the control eyes (injected RPE cells and PBS).

CONCLUSIONS

These results indicate that etoposide would be an adjunctive for the prevention of PVR. Further pharmacokinetic study of the intravitreal injection of etoposide is required.

Intraocular implants for extended drug delivery: therapeutic applications

An overview of ocular implants with therapeutic application potentials is provided. Various types of implants can be used as slow release devices delivering locally the needed drug for an extended period of time. Thus, multiple periocular or intraocular injections of the drug can be circumvented and secondary complications minimized. The various compositions of polymers fulfilling specific delivery goals are described. Several of these implants are undergoing clinical trials while a few are already commercialized. Despite the paramount progress in design, safety and efficacy, the place of these implants in our clinical therapeutic arsenal remains limited. Miniaturization of the implants allowing for their direct injection without the need for a complicated surgery is a necessary development avenue. Particulate systems which can be engineered to target specifically certain cells or tissues are another promising alternative. For ocular diseases affecting the choroid and outer retina, transscleral or intrasscleral implants are gaining momentum.

Antisense oligonucleotide targeting c-fos mRNA limits retinal pigment epithelial cell proliferation: a key step in the progression of proliferative vitreoretinopathy

The purpose of this work was to investigate the effect of c-fos antisense oligonucleotide (c-fos-AS-ON) on proliferative vitreoretinopathy (PVR). Cultures of human retinal pigment epithelial (hRPE) cells were established from adult human corneal donors. These cells were positively stained for cytokeratins. C-fos-AS-ON effect on serum-stimulated cell proliferation was estimated by evaluating the incorporation of 5-bromo-2'-deoxy-uridine (BrdU) into cellular DNA. Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting were respectively performed to quantify the serum-stimulated c-fos gene mRNA and protein expression in hRPE cells. Eight rabbits (16 eyes) were divided into c-fos-AS-ON treatment group and control group. 2.5 x 10(5) cultured hRPE cells were injected into the vitreous cavity of eyes to establish a PVR model. Prevalence of PVR and retinal detachment were determined by indirect ophthalmoscopy on days 1, 3, 7, 14, 21 and 28 post-injection and by pathological study on days 28 post-injection. The results showed that blocking the expression of c-fos by the addition of c-fos-AS-ON to the culture medium significantly inhibited the hRPE cells proliferation. This effect of c-fos-AS-ON was found to be sequence specific (the use of a sense or a mismatch sense oligonucleotide had no such an effect) and dose-dependent (0.375 microM was the lowest effective dose tested). Growth inhibition by c-fos-AS-ON remained for at least 72 h. By using RT-PCR and Western blotting, we found that the c-fos-AS-ON could specifically inhibit c-fos mRNA and protein synthesis in cultured hRPE cells. Though the eyes injected with c-fos-AS-ON also developed features of PVR, the severities of days 14, 21 and 28 post-injection were significantly lower than those in the control eyes (P<0.05). We conclude that c-fos-AS-ON can inhibit cultured hRPE cell proliferation, which mechanism may relate to blocking the expression of c-fos and can reduce the prevalence of experimental PVR. These findings establish a rationale for investigating the potential use of a c-fos-AS-ON as a novel therapeutical tool in the treatment of PVR.

Experimental model for proliferative vitreoretinopathy by intravitreal dispase: limited by zonulolysis and cataract

BACKGROUND

The intravitreal injection of dispase has been shown to be a valuable method for induction of experimental PVR. The goal of the present study was to gain additional information about potential side effects associated with this method.

METHODS

Twenty-one pigmented rabbits received a single injection of dispase under topical anesthesia to one eye only, contralateral eyes served as untreated control. The animals were injected with doses from 0.045 to 0.065 units of dispase: 8 animals received 0.045 units, 9 animals 0.055 units and 4 animals 0.065 units.

RESULTS

Proliferative vitreoretinopathy occurred in 81% of the treated eyes. In 90% cataract formation was observed. Lens luxation was present in 47.3% of the cataract eyes.

CONCLUSION

Intravitreal injection of dispase resulted in the reproducible induction of PVR in addition to cataract formation and lens luxation. Whether these effects may all be associated with a toxic reaction or whether the proliferative changes are solely triggered by endogenous reactions similar to the pathomechanism of human PVR and whether the cataract formation and the lens luxation may be avoided by changing the method of injection require further investigation.

A mouse model of proliferative vitreoretinopathy induced by dispase

A proliferative vitreoretinopathy-like condition induced by intravitreal dispase injection in C57BL/6J mice was studied using ophthalmoscopic and histochemical procedures. The frequency of intravitreal hemorrhage, intravitreal spots, retinal folds and epiretinal membranes was scored by ophthalmoscopic examination at 1, 2, 4, 6 and 8 weeks after the injection. Intravitreal spots corresponded to free cells exhibiting F4/80 immunoreactivity, a macrophage/microglial marker. Retinal folds always appeared before an epiretinal membrane could be observed. Dispase-injected eyes always showed a much higher frequency of folds and membranes than saline-injected eyes. Folds and membranes appeared earlier and were more extensive in the presence of intravitreal hemorrhage than in its absence. Müller retinal cells exhibited significant changes in glial fibrillary acidic protein-immunoreactivity. This was absent in normal Müller cells but, in dispase-injected animals, it was expressed in radial processes at the site of retinal folds, later extending to the whole retina. Both epi- and subretinal membranes contained cells probably derived from Müller cells, since they exhibited co-localization of glial fibrillary acidic protein- and glutamine synthase immunoreactivities. F4/80 was also present in numerous cells within the retina, epi- and subretinal membranes. By contrast, the retinal pigment epithelium cell marker RPE65 was restricted to subretinal membranes. It can be concluded that dispase induced a proliferative vitreoretinopathy-like condition in mice, with a strong contribution of macrophage- and glial-derived cells.

Photoreceptor-specific expression of platelet-derived growth factor-B results in traction retinal detachment

Expression of platelet-derived growth factor (PDGF)-A and PDGF-B is increased in patients with proliferative retinopathies in which traction retinal detachments occur. Previous studies have demonstrated that increased expression of PDGF-A in the retina of transgenic mice results in retinal gliosis due to proliferation of astrocytes with different retinal phenotypes based on the time of onset and location of the PDGF-A production. In this study, we investigated the effects of PDGF-B in the retina using gain-of-function transgenic mice that express PDGF-B in photoreceptors. These mice show proliferation of astrocytes, pericytes, and, to a lesser extent, endothelial cells, resulting in ectopic cells on the surface and extending into the retina. The sheets of cells exert traction on the retina resulting in traction retinal detachments similar to those seen in humans with proliferative retinopathies. These studies suggest that PDGF-B has more dramatic effects in the retina than PDGF-A, because it acts on additional cell types, in particular on pericytes, which have a highly developed contractile apparatus. These studies in the retina suggest a means that could be used in other tissues throughout the body to achieve graded PDGF effects. They also provide a new model of traction retinal detachment that can be used to investigate new treatments for patients with proliferative retinopathies.

Src family kinases negatively regulate platelet-derived growth factor alpha receptor-dependent signaling and disease progression

We tested the hypothesis that Src family kinases (SFK) contribute to c-Cbl-mediated degradation of the platelet-derived growth factor (PDGF) alpha receptor (alphaPDGFR). Using either a receptor mutant that does not engage SFKs (F72/74), or cells that that lack SFKs, we found that SFKs contributed to degradation of the alphaPDGFR. Overexpression of c-Cbl also reduced the receptor half-life, but only if the receptor was able to engage SFKs. In cultured cells, prolonging the half-life of the receptor correlated with enhanced signaling and more efficient S phase entry, whereas accelerating receptor degradation had the opposite effect. Consistent with these tissue culture findings, there was a statistically significant increase in the onset of a proliferative retinal disease when animals were injected with cells expressing the F72/74 receptor, as compared with cells expressing the WT receptor. Our findings suggest that SFKs cooperate with c-Cbl to negatively regulate the alphaPDGFR, and that the SFK/c-Cbl suppression of alphaPDGFR output is relevant to the onset and progression of a proliferative disease.

Dedifferentiation of the retinal pigment epithelium compared to the proliferative membranes of proliferative vitreoretinopathy

PURPOSE

To examine the gene expression for melanogenesis of retinal pigment epithelial cells during dedifferentiation and to compare the condition to that of eyes obtaining anatomical success after surgery for proliferative vitreoretinopathy.

METHODS

Gene expression for melanogenesis was determined by reverse transcriptase-polymerase chain reaction of tyrosinase and tyrosinase-related protein-1 genes in normal and cultured retinal pigment epithelial cells and in proliferative membranes in patients with proliferative vitreoretinopathy.

RESULTS

Gene expression for melanogenesis was classified into three types during dedifferentiation of retinal pigment epithelial cells: (1) tyrosinase-related protein-1 gene expression, (2) tyrosinase and tyrosinase-related protein-1 gene expression and (3) no expression of these genes. The expression of these genes were maintained better in mediums with basic fibroblast growth factor than in medium without basic fibroblast growth factor. Of the anatomically unsuccessful patients with proliferative vitreoretinopathy treated by surgery, 76.9% showed both tyrosinase and tyrosinase-related protein-1 gene expression; only 20% of the anatomically successful patients showed the gene expression.

CONCLUSIONS

We reported three different conditions of retinal pigment epithelial cells based on gene expression for melanogenesis during dedifferentiation. The different condition of the retinal pigment epithelial cells may have some relationship to the anatomical results for proliferative vitreoretinopathy surgery.

13-cis-retinoic acid in silicone-fluorosilicone copolymer oil in a rabbit model of proliferative vitreoretinopathy

The purpose of this study was to evaluate the effect of 13-cis-Retinoic Acid (RA) in Silicone-Fluorosilicone Copolymer Oil (SiFO) in a rabbit model of proliferative vitreoretinopathy (PVR). Rabbits underwent gas-compression vitrectomy. During gas-SiFO exchange, group 1 was injected with 1 ml (10 microg ml-1) 13-cis-RA in SiFO, group 2 with 1.5 ml (9 microg 1.5 ml-1) all-trans-RA in SiFO, group 3 with 1 ml SiFO alone, and group 4 with balanced salt solution (BSS). Groups 1-4 were also injected with 0.1 ml suspension of fibroblasts (75,000 0.1 ml-1) and 0.05 ml platelet rich plasma (70,000 0.1 ml-1), and were observed for 4 weeks. Group 5 was injected with SiFO alone, group 6 with 1 ml (10 microg ml-1) 13-cis-RA in SiFO, group 7 with 1.5 ml (9 microg 1.5 ml-1) all-trans-RA in SiFO, and group 8 with BSS. After 4 weeks, groups 5-7 underwent SiFO-BSS exchange. ERG and histopathology were performed to test for retinal toxicity in groups 5-8. The incidence of traction retinal detachment at 4 weeks was: group 1, 42.9%; group 2, 36.4%; group 3, 87.5%; and group 4, 88.9%. A significant difference in the incidence of PVR was noted between treated eyes (groups 1 and 2) and control eyes (groups 3 and 4) at 2, 3, and 4 weeks (P<0.05). No significant difference in the incidence of PVR was found between groups 1 and 2 during the same observation periods. ERG and histopathological studies showed no differences between the treated and the control fellow eyes (group 5-7) after 4 weeks. 13-cis-RA in SiFO (10 microg ml-1) is as effective as all-trans-RA in SiFO (9 microg 1.5 ml-1) in controlling the incidence of PVR when used for short term retinal tamponade and does not appear to be associated with retinal toxicity.

Antiproliferative effect of retinoic acid in 1% sodium hyaluronate in an animal model of PVR

PURPOSE

To determine the antiproliferative activity in intravitreous retinoic acid (RA) dispersed in 1% sodium hyaluronate (HA).

METHODS

Six groups of pigmented rabbits underwent gas-compression vitrectomy. Four days later, gas/HA or gas/balanced salt solution (BSS) exchange (1.0 m1) was performed in all rabbits. Groups A (n = 10) and B (n = 5) received intravitreous RA dissolved in 0.01 m1 of ethanol and dispersed in 1% HA (10 and 15 micrograms RA/m1, respectively). Group C (n = 10) received intravitreous RA dissolved in ethanol and dispersed in BSS (10 micrograms RA/m1). Groups D (n = 5) and F (n = 4) received 1 m1 of HA with ethanol; group E (n = 5) received 1 m1 of HA without ethanol. All groups except group F also received homologous fibroblasts and autologous, platelet-rich plasma intravitreously. The eyes were examined ophthalmoscopically for 1 month. Proliferative vitreoretinopathy (PVR) findings were graded according to the classification of Fastenberg et al. all group F eyes also were examined by light and electron microscopy.

RESULTS

RA in HA lessened PVR progression within 1 month when compared with HA injection controls and within 2 weeks when compared with the RA in BSS treatment group (both, p < 0.05). NO specific change attributable to ethanol was observed histopathologically.

CONCLUSION

RA dissolved in ethanol and dispersed in HA could be useful to treat PVR when silicone oil is unnecessary.

Suppression of experimental proliferative vitreoretinopathy by sustained intraocular delivery of 5-FU

Treatment of proliferative vitreoretinopathy (PVR) requires a multidimensional approach. Recent studies have focused on pharmacologic techniques to inhibit intraocular cell proliferation by applying antimetabolite drugs. Side effects associated with these drugs and difficulties in achieving effective concentration inside the eye make drug delivery an important and difficult part of this approach. We have developed a sustained-release bioerodible device with modifiable release properties for intraocular drug delivery. In this study, we evaluated the efficacy of the device with two different concentrations of 5-fluorouracil (5-FU) in an experimental model of PVR in rabbit eyes. Both devices showed significant (P < 0.05) efficacy in prevention of PVR. Devices containing 20% 5-FU (total of 1 mg) were 100% effective in prevention of tractional retinal detachment. No significant complications, other than mild vitreous hemorrhage in a few cases, were associated with this method. Because pharmacologic therapy is used as an augmenting method to surgical therapy, these devices can be easily implanted inside the eye through a sclerotomy at the completion of surgery without any discomfort to patients. Slow release of drug by this method reduces the incidence of toxicity and increases the efficacy by providing a constant concentration of drug during the active period of the disease.

Growth inhibition of human Tenon's capsule fibroblasts and rabbit dermal fibroblasts with non-carcinogenic N-alkylated anthracyclines

Bleb fibrosis after glaucoma filtering surgery and proliferative vitreoretinopathy after retinal detachment surgery are complications caused by proliferation of fibroblasts or fibroblastlike cells. The anthracycline daunomycin (DNM) has been used for treatment of those proliferative processes in humans. However, complications such as conjunctival necrosis and corneal or scleral ulcerations have been reported after administration of DNM to glaucoma patients. Intravitreal administration of DNM in rabbit eyes resulted in morphological and functional retinal damage. DNM also has the undesired general effect of carcinogenicity. N-Alkylation of the aminosugar moiety of DNM results in reduction or loss of carcinogenicity. We evaluated the inhibitory effect of the new non-carcinogenic N-alkylated analogues aclacinomycin A (ACA), N,N-dimethyladriamycin (AD280), and N-trifluoroacetyladriamycin-14-O-hemiadipate (AD143) on the growth of cultured human Tenon's capsule fibroblasts and rabbit dermal fibroblasts. Using DNM as a positive control, we conducted proliferation assays that demonstrated that ACA and AD280 inhibited fibroblast growth as effectively as DNM. AD143 was less efficacious. The magnitude of cellular growth inhibition was concentration dependent for all drugs tested. Extension of exposure times resulted in increased rates of cell death. Our in vitro studies suggest that further evaluation of ACA and AD280 should be carried out in animal models of ocular proliferative disorders.

Traction retinal detachment. XLIX Edward Jackson Memorial Lecture

This review had two main objectives. The first goal was to attempt to define a final common pathway for traction retinal detachment. To illustrate this, I considered the following three common clinical entities: penetrating ocular trauma, proliferative vitreoretinopathy, and proliferative diabetic retinopathy. My second goal was to emphasize the role of research in developing a rational approach to treatment. To illustrate the second goal, I reviewed the contributions from three realms of research--laboratory, animal, and clinical research--examining their interactions and considering their roles in our current understanding and management of these clinical entities.

Dispersion of retinal pigment epithelial cells from experimental retinal holes

The effects of cryotherapy, transcleral massage, or directed irrigation on exposed retinal pigment epithelial (RPE) cells at the base of an experimental retinal hole were studied in living rabbit eyes. Cryotherapy or massage with or without vitrectomy failed to release RPE cells or result in preretinal membrane formation. Directed irrigation dispersed viable RPE cells into the vitreous and produced cellular precipitates with membranes on the inferior retina, although the membranes tended to regress within 6 weeks after surgery. These results suggest that healthy RPE cells at the base of retinal tears are not easily released into the vitreous and may not contribute to the formation of preretinal membranes found in proliferative vitreoretinopathy.

Clearance rate of macrophages from the vitreous in rabbits

Macrophages are usually present in epiretinal membranes from eyes with proliferative vitreoretinopathy (PVR). Information on the kinetics of macrophages in the eye may be of help in identifying their role in this disease. To determine the half-life of macrophages in the vitreous, peritoneal macrophages were labeled by allowing them to phagocytose 141Cerium (gamma-emitter) labeled microspheres, and were then injected into the vitreous of the same rabbit from which they were obtained. The animals were sacrificed at various times post-injection and the radioactivity remaining in the vitreous was measured. Using this procedure, the half-life was found to be 4.8 days.

Proliferative vitreoretinopathy--is it anything more than wound healing at the wrong place?

Proliferative vitreoretinopathy (PVR) is a reactive process of the ocular tissue after perforating trauma, retinal detachment, and surgical manipulations. Although several studies, most of them experimental, have focused on the detection of specific etiologic factors in the development of PVR, there is compelling evidence that PVR is nothing more than a physiologic tissue repair process with undesirable consequences for the retina. Important features of PVR involving the role of platelets, mononuclear phagocytes, and fibroblasts parallel the chain of events observed in tissue repair elsewhere in the body. Numerous experimental models for PVR, originally designed to find specific stimuli for the generation of intraocular traction membrane formation, have shown that the process of PVR is the common pathway of the eye's reaction to vitreoretinal trauma of any kind. Accordingly, vitreoretinal surgeons could learn a lot from the work of other disciplines, e.g. surgery and dermatology, on wound healing, and the factors known to modify wound healing elsewhere in the body should be taken into consideration. The well-established impairment of tissue repair processes caused by medical treatment with corticosteroids and cytotoxic agents suggests a combined medical approach to PVR as an adjunct to surgical treatment, using refined methods of application and dosage. Steroids and cytotoxic drugs will influence the course of PVR by suppressing macrophage recruitment and the initial inflammatory reaction as well as the proliferative phase of wound healing with traction retinal detachment, respectively.

Autoimmune responsiveness to retinal IRBP, S-antigen and opsin in proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) was induced in rabbits by intravitreal injection of homologous fibroblasts. During the 8 weeks after injection the immune responsiveness to three purified retinal autoantigens was studied. From 2 weeks after injection, animals that developed serious forms of PVR exhibited definite mitotic responses of their lymphocytes to stimulation by the retinal antigens. These responses could consistently be demonstrated for S-antigen and interphotoreceptor retinoid-binding protein (IRBP) during the subsequent period of examination. Marked responses were also noted to opsin, however, their occurrence was more variable. In mild forms of PVR or in controls the responses were weak or absent. This showed that the elevated cellular reactivities were induced by the development of PVR and not by some other experimental factor. Humoral immune responses to the three antigens were absent (as assayed by ELISA). The control groups did not exhibit any elevated immune responsiveness. There appears to be accumulating evidence that inflammation may play a role in the development of PVR. The present results indicate that cellular autoimmune responses to photoreceptor antigens are a secondary phenomenon in PVR, nevertheless, they may be an important factor in the subsequent development of severe PVR. This autosensitization may consequently be taken into consideration in the treatment of complicated human PVR.

Focal irradiation of perforating eye injuries

Plaques constructed with 125I were used to irradiate the sites of perforating ocular injuries in rabbits. An approximate dose of 16Gy given over a period of 6 days was shown to significantly reduce intraocular cellular proliferation when irradiation was commenced within 24 hours after injury. If irradiation was delayed until day 5, this reduction in cellular proliferation and intraocular membrane formation did not occur. Smaller radiation doses of approximately 6Gy given within 24 hours post-injury and administered over 6 days also reduced the extent of cellular proliferation but was not as effective as the 16Gy dose.

Posterior penetrating injury in the rabbit eye: effect of blood and ferrous ions

The effects of intravitreal injections of blood or ferrous chloride solutions on experimental posterior penetrating eye injury in the rabbit are described. An 8-mm standard posterior penetrating wound, without additional manipulation, healed without retinal detachment or membrane formation. Injection into the vitreous cavity of blood or ferrous chloride solution in addition to the wound resulted in fibroblastic proliferation with membrane formation. A critical amount of blood or iron solution was associated with marked traction and traction retinal detachment. Severe inflammation in association with the development of thick intravitreal membranes was also observed in eyes receiving the ferrous chloride solutions, the extent of which was related to the severity of the retinal detachment. These results show that iron is an important stimulus to inflammation and to intravitreal fibroblastic proliferation in rabbit eyes with posterior penetrating eye injuries.