Sorafenib prevents human retinal pigment epithelium cells from light-induced overexpression of VEGF, PDGF and PlGF

Smart Nanocarriers for the Treatment of Retinal Diseases

Retinal diseases, such as age-related macular degeneration, diabetic retinopathy, and retinoblastoma, stand as the leading causes of irreversible vision impairment and blindness worldwide. Effectively administering drugs for retinal diseases poses a formidable challenge due to the presence of complex ocular barriers and elimination mechanisms. Over time, various approaches have been developed to fabricate drug delivery systems for improving retinal therapy including virus vectors, lipid nanoparticles, and polymers. However, conventional nanocarriers encounter issues related to the controllability, efficiency, and safety in the retina. Therefore, the development of smart nanocarriers for effective or more invasive long-term treatment remains a desirable goal. Recently, approaches have surfaced for the intelligent design of nanocarriers, leveraging specific responses to external or internal triggers and enabling multiple functions for retinal therapy such as topical administration, prolonged drug release, and site-specific drug delivery. This Review provides an overview of prevalent retinal pathologies and related pharmacotherapies to enhance the understanding of retinal diseases. It also surveys recent developments and strategies employed in the intelligent design of nanocarriers for retinal disease. Finally, the challenges of smart nanocarriers in potential clinical retinal therapeutic applications are discussed to inspire the next generation of smart nanocarriers.

Recent Advances in Age-Related Macular Degeneration Therapies

Age-related macular degeneration (AMD) was described for the first time in the 1840s and is currently the leading cause of blindness for patients over 65 years in Western Countries. This disease impacts the eye’s posterior segment and damages the macula, a retina section with high levels of photoreceptor cells and responsible for the central vision. Advanced AMD stages are divided into the atrophic (dry) form and the exudative (wet) form. Atrophic AMD consists in the progressive atrophy of the retinal pigment epithelium (RPE) and the outer retinal layers, while the exudative form results in the anarchic invasion by choroidal neo-vessels of RPE and the retina. This invasion is responsible for fluid accumulation in the intra/sub-retinal spaces and for a progressive dysfunction of the photoreceptor cells. To date, the few existing anti-AMD therapies may only delay or suspend its progression, without providing cure to patients. However, in the last decade, an outstanding number of research programs targeting its different aspects have been initiated by academics and industrials. This review aims to bring together the most recent advances and insights into the mechanisms underlying AMD pathogenicity and disease evolution, and to highlight the current hypotheses towards the development of new treatments, i.e., symptomatic vs. curative. The therapeutic options and drugs proposed to tackle these mechanisms are analyzed and critically compared. A particular emphasis has been given to the therapeutic agents currently tested in clinical trials, whose results have been carefully collected and discussed whenever possible.

Tissue engineering in age-related macular degeneration: a mini-review

Age-related macular degeneration (AMD) is a progressive, degenerative disease of the macula, leading to severe visual loss in the elderly population. There are two types of AMD: non-exudative ('dry') AMD and exudative ('wet') AMD. Non-exudative AMD is characterized by drusen formation and macular atrophy, while the blood vessels are not leaky. Exudative AMD is a more advanced form of the disease, featured with abnormal blood vessel growth and vascular leakage. Even though anti-angiogenic therapies have been effective in treating wet AMD by normalizing blood vessels, there is no treatment available to prevent or treat dry AMD. Currently, the mechanisms of drusen formation and macular atrophy in the dry AMD are poorly understood, in part because the currently available in vivo models of AMD could not decouple and isolate the complex biological and biophysical factors in the macular region for a detailed mechanism study, including the complement system, angiogenesis factors, extracellular matrix, etc. In the present review article, we describe the biological background of AMD and the key cells and structures in AMD, including retinal epithelium, photoreceptor, Bruch's membrane, and choriocapillaris. We also discuss pre-clinical animal models of AMD and in vivo tissue-engineered approaches, including cell suspension injection and organoid-derived cell sheet transplantation. We also discuss in vitro tissue-engineered models for AMD research. Specifically, we evaluate and compare currently available two- and three-dimensional AMD tissue-engineered models that mimic key anatomical players in AMD progression, including pathophysiological characteristics in Bruch's membrane, photoreceptor, and choriocapillaris. Finally, we discuss the limitation of current AMD models and future directions.

Sorafenib Repurposing for Ophthalmic Delivery by Lipid Nanoparticles: A Preliminary Study

Uveal melanoma is the second most common melanoma and the most common intraocular malignant tumour of the eye. Among various treatments currently studied, Sorafenib was also proposed as a promising drug, often administered with other compounds in order to avoid resistance mechanisms. Despite its promising cellular activities, the use of Sorafenib by oral administration is limited by its severe side effects and the difficulty to reach the target. The encapsulation into drug delivery systems represents an interesting strategy to overcome these limits. In this study, different lipid nanoparticulate formulations were prepared and compared in order to select the most suitable for the encapsulation of Sorafenib. In particular, two solid lipids (Softisan or Suppocire) at different concentrations were used to produce solid lipid nanoparticles, demonstrating that higher amounts were able to achieve smaller particle sizes, higher homogeneity, and longer physical stability. The selected formulations, which demonstrated to be biocompatible on Statens Seruminstitut Rabbit Cornea cells, were modified to improve their mucoadhesion, evaluating the effect of two monovalent cationic lipids with two lipophilic chains. Sorafenib encapsulation allowed obtaining a sustained and prolonged drug release, thus confirming the potential use of the developed strategy to topically administer Sorafenib in the treatment of uveal melanoma.

A dynamic nomogram for predicting diabetic macular edema in type 2 diabetes patients based on plasma cytokines

OBJECTIVE

This study investigated changes of plasma cytokines and aimed to build a dynamic nomogram for diabetic macular edema (DME) in type 2 diabetes mellitus (T2DM).

METHODS

In a pilot cohort, plasma samples were selected from 9 T2DM patients and 9 DME patients to screen for cytokine differences. The screening cytokines were then validated by enzyme-linked immunoassay in a cohort, which contained 100 DME (DME group) and 100 T2DM patients without DME (T2DM group). A dynamic nomogram for predicting DME was developed, based on the plasma cytokines.

RESULTS

In the pilot cohort, 11 plasma cytokines were significantly increased in the DME group. In the validation cohort, platelet-derived growth factor (PDGF)-BB, tissue inhibitors of metalloproteinase (TIMP)-1, angiopoietin (ANG-1), and vascular endothelial cell growth factor receptor (VEGFR)-2 were confirmed to be significantly elevated in the DME group. The dynamic nomogram demonstrated good calibration and discrimination, with an area under the receiver operating characteristic curve (AUC) of 0.88. In the test set, sensitivity, specificity, and AUC were 73.3%, 80.0%, and 0.84, respectively.

CONCLUSION

Plasma cytokines were closely associated with DME. A novel dynamic monogram including ANG-1, PDGF-BB, TIMP-1, and VEGFR2 was a novel tool for predicting DME.

Experimental Models in Neovascular Age Related Macular Degeneration

Neovascular age-related macular degeneration (vAMD), characterized by the neo-vascularization of the retro-foveolar choroid, leads to blindness within few years. This disease depends on angiogenesis mediated by the vascular endothelial growth factor A (VEGF) and to inflammation. The only available treatments consist of monthly intravitreal injections of antibodies directed against VEGF or VEGF/VEGFB/PlGF decoy receptors. Despite their relative efficacy, these drugs only delay progression to blindness and 30% of the patients are insensitive to these treatments. Hence, new therapeutic strategies are urgently needed. Experimental models of vAMD are essential to screen different innovative therapeutics. The currently used in vitro and in vivo models in ophthalmic translational research and their relevance are discussed in this review.

Blue-violet light decreases VEGFa production in an in vitro model of AMD

Blue light is an identified risk factor for age-related macular degeneration (AMD). The production of vascular endothelial growth factor (VEGF), leading to neovascularization, is a major complication of the wet form of this disease. We investigated how blue light affects VEGF expression and secretion using A2E-loaded retinal pigment epithelium (RPE) cells, a cell model of AMD. Incubation of RPE cells with A2E resulted in a significant increase in VEGF mRNA and, intracellular and secreted VEGF protein levels, but not mRNA levels of VEGFR1 or VEGFR2. Blue light exposure of A2E-loaded RPE cells resulted in a decrease in VEGF mRNA and protein levels, but an increase in VEGFR1 levels. The toxicity of 440 nm light on A2E-loaded RPE cells was enhanced by VEGF supplementation. Our results suggest that age-related A2E accumulation may result in VEGF synthesis and release. This synthesis of VEGF, which enhances blue light toxicity for the RPE cells, is itself suppressed by blue light. Anti-VEGF therapy may therefore improve RPE survival in AMD.

Increased choroidal thickness: a new feature to monitor age-related macular degeneration recurrence

PURPOSE

The main objective of this study was to assess choroidal thickness (CT) changes during an exudative recurrence of age-related macular degeneration (AMD).

METHODS

A real-life prospective non-interventional 9-month study was conducted in two centers in consecutive patients with exudative AMD between November 2016 and July 2017. CT was measured manually in both eyes based on enhanced-depth imaging spectral-domain optical coherence tomography at different follow-up visits scheduled in the morning.

RESULTS

A total of 134 patients were included. Ninety-five patients presented at least one episode, defined by a follow-up visit under controlled condition (dry retina) followed by a visit for exudative recurrence. A total of 119 episodes were analyzed. The mean CT change in the treated eye was + 8.45 ± 13.52 μm (p < 0.001) and + 5.62 ± 14.77 μm (p = 0.009) respectively in the subfoveal area and nasal area. No significant change in CT was observed in the fellow eye. No significant association between CT changes and treatment, number of intravitreal injections, and blood pressure was observed.

CONCLUSION

CT increased in case of exudative recurrence of neovascular AMD. The increase was mild but significant. Thus, CT could be used as a monitoring criterion, like the central retinal thickness, in AMD management.

Essential Role of mTOR Signaling in Human Retinal Pigment Epithelial Cell Regeneration After Laser Photocoagulation

This study assessed the role of mechanistic target of rapamycin (mTOR) pathway in the human adult retinal pigment epithelial (ARPE) cell response after laser photocoagulation (LP). The effect of mTOR inhibition on ARPE-19 cell was investigated by rapamycin treatment after LP. Cell viability and proliferation were explored using MTT and EdU assays, respectively. The expression of mTOR-related proteins and epithelial-mesenchymal transition (EMT) markers was verified by Western blot. Rapamycin retarded the LP area recovery in a dose-dependent manner by the 120 h, while LP+DMSO vehicle-treated cells completely restored the lesion zone (P ≤ 0.01). ARPE-19 cell viability is significantly lower in LP + rapamycin 80 and 160 ng/ml treated cultures compared to LP control at 120 h (P ≤ 0.001). LP control group demonstrated significantly more proliferative cells compared to untreated cells at the 72 and 120 h, whereas EdU-positive cell numbers in cultures treated with rapamycin at concentrations of 80 and 160 ng/ml were similar to baseline values (P ≤ 0.01). mTOR pathway activation is essential for regulation of the RPE cell migration and proliferation after LP. mTOR inhibition with rapamycin effectively blocks the migration and proliferation of the RPE cells. Our results demonstrate that mTOR has an important role in ARPE-19 cell as a regulator of cell behavior under stress conditions, suggesting that mTOR could be a promising therapeutic target for numerous retinal diseases.

The Effects of Anti-Vascular Endothelial Growth Factor Drugs on Retinal Pigment Epithelial Cell Culture

Objectives:

To assess the effects of anti-vascular endothelial growth factor (VEGF) drugs on retinal pigment epithelium cell culture.

Materials and Methods:

Aflibercept (0.5 mg/mL), bevacizumab (0.3125 mg/mL), and ranibizumab (0.125 mg/mL) were applied to retinal pigment epithelium cell cultures isolated from the enucleated eyes of New Zealand white rabbits. Viability, apoptosis, proliferation, and senescence of the cells were evaluated in control and drug-treated cultures at the end of 72 hours.

Results:

Cells treated with aflibercept showed increased viability and decreased apoptosis compared to the control culture and both the bevacizumab- and ranibizumab-treated groups (p<0.05). Statistically increased apoptosis and decreased viability were found in the bevacizumab and ranibizumab-treated groups compared with the control group (p<0.05). There were no statistically significant differences in cell proliferation and senescence between the groups (p>0.05).

Conclusion:

Anti-VEGF drugs did not affect senescence or proliferation of retinal pigment epithelium cells. Aflibercept was found to decrease apoptosis and increase cell viability, while ranibizumab and bevacizumab increased apoptosis and reduced cell viability in retinal pigment epithelium culture.

Intravitreal aflibercept protects photoreceptors of mice against excessive light exposure

Our previous studies found that an anti-placental growth factor (PlGF) antibody protected the retina in light-induced retinal damage model, a model of non-exudative age-related macular degeneration (AMD). Aflibercept is an inhibitor of vascular endothelial growth factor (VEGF) and PlGF. In present study, we revealed that the intravitreal injection of aflibercept lessens light-induced retinal damage, while anti-VEGF antibody has no effect on the light-exposed retina. Moreover, PlGF disrupted the tight junctions between the human retinal pigment epithelial cells in vitro, and aflibercept blocked the disruption. These data suggest that the aflibercept may be an effective treatment of non-exudative AMD.

Circulating vascular endothelial growth factor (VEGF) as predictive factor of progression-free survival in patients with advanced chordoma receiving sorafenib: an analysis from a phase II trial of the french sarcoma group (GSF/GETO)

Background

Patients with advanced chordoma are often treated with tyrosine kinase inhibitors without any predictive factor to guide decision. We report herein an ancillary analysis of the the Angionext phase II trial (NCT 00874874).

Results

From May 2011 to January 2014, 26 were sampled. The 9-month PFS rate was 72.9% (95%-CI: 45.9-87.9). During sorafenib treatment, a significant increase in PlGF (18.4 vs 43.8 pg/mL, p<0.001) was noted along with a non-significant increase in VEGF (0.7 vs 1.0 ng/mL, p=0.07). VEGF at D1 >1.04 ng/mL (HR=12.5, 95%-CI: 1.37-114, p=0.025) and VEGF at D7 >1.36 ng/mL (HR=10.7, 95%-CI: 1.16-98, p=0.037) were associated with shorter PFS. The 9-month PFS rate was 92.3% (95%-CI: 56.6-98.9) when VEGF at D1 was ≤1.04 ng/mL versus 23.3% (95%-CI: 1.0-63.2) when >1.04 ng/mL.

Patients and Methods

Chordoma patients were treated with sorafenib 800 mg/day for 9 months, unless earlier occurrence of progression or toxicities. Six biomarkers (sE-Selectin, VEGF, VEGF-C, placental growth factor (PlGF), Thrombospondin, Stem Cell Factor (SCF)) were measured at baseline (day 1: D1) and day 7 (D7).

Conclusion

High levels of VEGF was associated with poor outcome.

Odorant Receptor 51E2 Agonist β-ionone Regulates RPE Cell Migration and Proliferation

The odorant receptor 51E2 (OR51E2), which is well-characterized in prostate cancer cells and epidermal pigment cells, was identified for the first time as the most highly expressed OR in human fetal and adult retinal pigment epithelial (RPE) cells. Immunofluorescence staining and Western blot analysis revealed OR51E2 localization throughout the cytosol and in the plasma membrane. Additionally, immunohistochemical staining of diverse layers of the eye showed that the expression of OR51E2 is restricted to the pigment cells of the RPE and choroid. The results of Ca²⁺-imaging experiments demonstrate that activation of OR51E2 triggers a Ca²⁺ dependent signal pathway in RPE cells. Downstream signaling of OR51E2 involves the activation of adenylyl cyclase, ERK1/2 and AKT. The activity of these protein kinases likely accounts for the demonstrated increase in the migration and proliferation of RPE cells upon stimulation with the OR51E2 ligand β-ionone. These findings suggest that OR51E2 is involved in the regulation of RPE cell growth. Thus, OR51E2 represents a potential target for the treatment of proliferative disorders.

Foveal structure during the induction phase of anti-vascular endothelial growth factor therapy for occult choroidal neovascularization in age-related macular degeneration

Purpose

To evaluate the efficacy of monthly injections of aflibercept and ranibizumab on foveal structure after three months, for the treatment of occult choroidal neovascularization (CNV) in age-related macular degeneration (AMD).

Methods

We retrospectively studied 103 eyes with treatment-naïve neovascular AMD with occult and no classic CNV. Seventy-four of 103 eyes were treated with ranibizumab (intravitreal ranibizumab injection [IVR] group); 29 eyes were treated with aflibercept (intravitreal aflibercept injection [IAI] group). The best-corrected visual acuity and the retinal and choroidal structure at the fovea were evaluated using optical coherence tomography.

Results

The total foveal thickness, the height of serous retinal detachments, and subfoveal choroidal thickness were compared with baseline, and the incidence of retinal pigment epithelial elevation significantly decreased in the IAI group compared with the IVR group. In contrast, the thickness of the sensory retina at the fovea significantly decreased in the IVR group when compared with the IAI group. The logarithm of the minimum angle of resolution (logMAR) best-corrected visual acuity improved more significantly in the IVR group (−0.085±0.164) than in the IAI group (−0.020±0.125) at 3 months (P=0.017).

Conclusion

After intravitreal injection, aflibercept more rapidly reduced subretinal fluid and subfoveal choroidal thickness. In contrast, ranibizumab decreased the sensory retinal thickness compared with aflibercept. The responses of the retinal and choroidal tissue to these anti-VEGF agents may be different during the induction phase for eyes with occult CNV secondary to neovascular AMD.

Paeonol Inhibits Proliferation of Vascular Smooth Muscle Cells Stimulated by High Glucose via Ras-Raf-ERK1/2 Signaling Pathway in Coculture Model

Paeonol (Pae) has been previously reported to protect against atherosclerosis (AS) by inhibiting vascular smooth muscle cell (VSMC) proliferation or vascular endothelial cell (VEC) injury. But studies lack how VSMCs and VECs interact when Pae plays a role. The current study was based on a coculture model of VSMCs and VECs to investigate the protective mechanisms of Pae on atherosclerosis (AS) by determining the secretory function of VECs and proliferation of VSMCs focusing on the Ras-Raf-ERK1/2 signaling pathway. VECs were stimulated by high glucose. Our data showed that high concentration (35.5 mM) of glucose induced damage in VECs. Injury of VECs stimulated VSMC proliferation in the coculture model. Pae (120  μ M) decreased vascular endothelial growth factor (VEGF) and platelet derivative growth factor B (PDGF-B) release from VECs and inhibited overexpression of Ras, P-Raf, and P-ERK proteins in VSMCs. The results indicate that diabetes modulates the inflammatory response in VECs to stimulate VSMC proliferation and promote the development of AS. Pae was beneficial by inhibiting the inflammatory effects of VECs on VSMC proliferation. This study suggests the inhibitory mechanism of Pae due to the inhibition of VEGF and PDGF-B secretion in VECs and Ras-Raf-ERK1/2 signaling pathway in VSMCs.

EGFR-blockade with erlotinib reduces EGF and TGF-β2 expression and the actin-cytoskeleton which influences different aspects of cellular migration in lens epithelial cells

INTRODUCTION

After cataract surgery, residual lens epithelial cells migrate and proliferate within the capsular bag resulting in posterior capsule opacification (PCO). The up-regulation of TGF-β2, EGF and FGF-2 has been identified as a key factor in PCO pathogenesis leading to actin fiber assembly and alterations in the migration pattern. In this in vitro study, the influence of Erlotinib as a selective EGFR inhibitor is investigated on the cellular features indicated, which might promote a future clinical application.

METHODS

Expression of EGF, FGF-2 and TGF-β2 was measured using RT-PCR and ELISA in human lens epithelial cells (HLEC). Computational data of an in vitro time lapse microscopy assay were used for statistical analysis of single cell migration with a particular focus on cell-cell interaction; cell velocity distribution; and displacement before, during and after mitosis. The effect of Erlotinib on the actin-cytoskeleton was evaluated using Alexa Fluor 488 Phalloidin and epifluorescence microscopy.

RESULTS

EGF and TGF-β2 mRNA expression and protein levels are reduced by Erlotinib, while FGF-2 expression remained stable. Overall fluidity of cell-cell interaction is less in the presence of Erlotinib compared to the control and the velocity distribution across all cells becomes less uniform within the cell cluster. After mitosis, HLEC move significantly faster without EGFR inhibition, which can be completely blocked by Erlotinib. Furthermore, Erlotinib diminishes the amount of actin stress fibers and the stress fiber diameter.

CONCLUSION

As a novel effect of Erlotinib on HLEC, we describe the down-regulation of EGF and TGF-β2 expression, both are crucial factors for PCO development. Cellular movement displays complex alterations under EGFR inhibition, which is partly explained by actin fiber depletion. These findings further underline the role of Erlotinib in pharmacologic PCO prophylaxis.

Temsirolimus inhibits proliferation and migration in retinal pigment epithelial and endothelial cells via mTOR inhibition and decreases VEGF and PDGF expression

Due to their high prevalence, retinal vascular diseases including age related macular degeneration (AMD), retinal vein occlusions (RVO), diabetic retinopathy (DR) and diabetic macular edema have been major therapeutic targets over the last years. The pathogenesis of these diseases is complex and yet not fully understood. However, increased proliferation, migration and angiogenesis are characteristic cellular features in almost every retinal vascular disease. The introduction of vascular endothelial growth factor (VEGF) binding intravitreal treatment strategies has led to great advances in the therapy of these diseases. While the predominant part of affected patients benefits from the specific binding of VEGF by administering an anti-VEGF antibody into the vitreous cavity, a small number of non-responders exist and alternative or additional therapeutic strategies should therefore be evaluated. The mammalian target of rapamycin (mTOR) is a central signaling pathway that eventually triggers up-regulation of cellular proliferation, migration and survival and has been identified to play a key role in angiogenesis. In the present study we were able to show that both retinal pigment epithelial (RPE) cells as wells as human umbilical vein endothelial cells (HUVEC) are inhibited in proliferating and migrating after treatment with temsirolimus in non-toxic concentrations. Previous studies suggest that the production of VEGF, platelet derived growth factor (PDGF) and other important cytokines is not only triggered by hypoxia but also by mTOR itself. Our results indicate that temsirolimus decreases VEGF and PDGF expression on RNA and protein levels significantly. We therefore believe that the mTOR inhibitor temsirolimus might be a promising drug in the future and it seems worthwhile to evaluate complementary therapeutic effects with anti-VEGF drugs for patients not profiting from mono anti-VEGF therapy alone.

Trophic factors in the pathogenesis and therapy for retinal degenerative diseases

Trophic factors are endogenously secreted proteins that act in an autocrine and/or paracrine fashion to affect vital cellular processes such as proliferation, differentiation, and regeneration, thereby maintaining overall cell homeostasis. In the eye, the major contributors of these molecules are the retinal pigment epithelial (RPE) and Müller cells. The primary paracrine targets of these secreted proteins include the photoreceptors and choriocapillaris. Retinal degenerative diseases such as age-related macular degeneration and retinitis pigmentosa are characterized by aberrant function and/or eventual death of RPE cells, photoreceptors, choriocapillaris, and other retinal cells. We discuss results of in vitro and in vivo animal studies in which candidate trophic factors, either singly or in combination, were used in an attempt to ameliorate photoreceptor and/or retinal degeneration. We also examine current trophic factor therapies as they relate to the treatment of retinal degenerative diseases in clinical studies.

Decorin inhibits angiogenic potential of choroid-retinal endothelial cells by downregulating hypoxia-induced Met, Rac1, HIF-1α and VEGF expression in cocultured retinal pigment epithelial cells

Choroidal neovascularization (CNV) is one of the most common causes of severe vision loss. Decorin, a multiple receptor tyrosine kinase inhibitor, has been recently shown to play an important regulatory role in angiogenic response. This study aims to investigate whether the overexpression of decorin in retinal pigment epithelial (RPE) cells under hypoxia alters the in vitro angiogenic ability of cocultured choroid-retinal endothelial cells and to explore the possible mechanisms involved. Human RPE cells (ARPE-19) were subjected to hypoxia with or without decorin pretreatment, and RNA interference technique was used to knock down the Met gene in ARPE-19 cells. Cell viability was determined using the Cell Counting Kit-8 assay. Expression of Met, Rac1 and hypoxia-inducible factor-1 alpha (HIF-1α) was evaluated by western blot and quantitative real-time polymerase chain reaction (qRT-PCR). Vascular endothelial growth factor (VEGF) expression was evaluated by enzyme-linked immunosorbent assay (ELISA) and qRT-PCR. We then constructed a recombinant lentiviral vector carrying the decorin gene to transduce ARPE-19 cells. The overexpression of decorin in transduced RPE cells was confirmed by qRT-PCR and western blot. The transduced RPE cells were then cocultured with rhesus macaque choroid-retinal endothelial cells (RF/6A) in a transwell coculture system to observe the effects of decorin overexpression in ARPE-19 cells on the proliferation, migration and tube formation of RF/6A cells. In response to hypoxia, the VEGF concentrations in the culture supernatants increased greatly at 24 and 48 h, and this effect was inhibited significantly and nearly equally in the presence of 50-200 nM decorin. Decorin pretreatment before hypoxia exposure effectively reduced the hypoxia-induced expression of Met, Rac1, HIF-1α and VEGF in ARPE-19 cells. Transfection of small interfering RNA against Met to ARPE-19 cells also resulted in significant downregulation of Rac1, HIF-1α and VEGF under hypoxia, and this effect was similar to that noted with decorin pretreatment alone or with their combination. Results from the coculture system showed that the overexpression of decorin in ARPE-19 cells significantly inhibited the proliferation, migration and tube formation of RF/6A cells. These results indicate that Met pathway activation plays an important role in the upregulation of VEGF in RPE cells under hypoxia. Decorin may interfere with angiogenesis by downregulating hypoxia-induced Met, Rac1, HIF-1α and VEGF expression in RPE cells, which suggests a potential strategy for the inhibition of CNV.

Hyperactivation of retina by light in mice leads to photoreceptor cell death mediated by VEGF and retinal pigment epithelium permeability

Light toxicity is suspected to enhance certain retinal degenerative processes such as age-related macular degeneration. Death of photoreceptors can be induced by their exposure to the visible light, and although cellular processes within photoreceptors have been characterized extensively, the role of the retinal pigment epithelium (RPE) in this model is less well understood. We demonstrate that exposition to intense light causes the immediate breakdown of the outer blood–retinal barrier (BRB). In a molecular level, we observed the slackening of adherens junctions tying up the RPE and massive leakage of albumin into the neural retina. Retinal pigment epithelial cells normally secrete vascular endothelial growth factor (VEGF) at their basolateral side; light damage in contrast leads to VEGF increase on the apical side – that is, in the neuroretina. Blocking VEGF, by means of lentiviral gene transfer to express an anti-VEGF antibody in RPE cells, inhibits outer BRB breakdown and retinal degeneration, as illustrated by functional, behavioral and morphometric analysis. Our data show that exposure to high levels of visible light induces hyperpermeability of the RPE, likely involving VEGF signaling. The resulting retinal edema contributes to irreversible damage to photoreceptors. These data suggest that anti-VEGF compounds are of therapeutic interest when the outer BRB is altered by retinal stresses.

Silibinin inhibits VEGF secretion and age-related macular degeneration in a hypoxia-dependent manner through the PI-3 kinase/Akt/mTOR pathway

BACKGROUND AND PURPOSE

Hypoxia-mediated neovascularization plays an important role in age-related macular degeneration (AMD). There are few animal models or effective treatments for AMD. Here, we investigated the effects of the flavonoid silibinin on hypoxia-induced angiogenesis in a rat AMD model.

EXPERIMENTAL APPROACH

Retinal pigmented epithelial (RPE) cells were subjected to hypoxia in vitro and the effects of silibinin on activation of key hypoxia-induced pathways were examined by elucidating the hypoxia-inducible factor-1 alpha (HIF-1α) protein level by Western blot. A rat model of AMD was developed by intravitreal injection of VEGF in Brown Norway rats, with or without concomitant exposure of animals to hypoxia. Animals were treated with oral silibinin starting at day 7 post-VEGF injection and AMD changes were followed by fluorescein angiography on days 14 and 28 post-injection.

KEY RESULTS

Silibinin pretreatment of RPE cells increased proline hydroxylase-2 expression, inhibited HIF-1α subunit accumulation, and inhibited VEGF secretion. Silibinin-induced HIF-1α and VEGF down-regulation required suppression of hypoxia-induced phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) pathway. In the rat model of AMD, silibinin administration prevented VEGF- and VEGF plus hypoxia-induced retinal oedema and neovascularization.

CONCLUSION AND IMPLICATIONS

The effects of silibinin, both in vitro and in vivo, support its potential as a therapeutic for the prevention of neovascular AMD.

PlGF: a multitasking cytokine with disease-restricted activity

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family that also comprises VEGF-A (VEGF), VEGF-B, VEGF-C, and VEGF-D. Unlike VEGF, PlGF is dispensable for development and health but has diverse nonredundant roles in tissue ischemia, malignancy, inflammation, and multiple other diseases. Genetic and pharmacological gain-of-function and loss-of-function studies have identified molecular mechanisms of this multitasking cytokine and characterized the therapeutic potential of delivering or blocking PlGF for various disorders.

Axitinib modulates hypoxia-induced blood-retina barrier permeability and expression of growth factors

This study investigates the effects of the multikinase inhibitor axitinib on the expression of vascular endothelial growth factor (VEGF) receptors 1/2 (VEGFR-1/2) and platelet-derived growth factor (PDGF) receptor beta (PDGFR-β), hypoxia-induced increased tissue permeability, occludin, zonula occludens protein 1 (ZO-1), VEGF-A, and PDGF expression of human retinal pigment epithelial (RPE) cells and human umbilical vein endothelial cells (HUVECs). Primary human RPE cells and HUVECs were exposed to hypoxia and axitinib. Viability of cells, tissue permeability, and expression of occludin, ZO-1, VEGF, PDGF, VEGFR-1/2 and PDGFR-β, and their mRNAs, were investigated by reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, and immunohistochemistry. Treatment with axitinib reduced expression of VEGFR-1/2 and PDGFR-β. Hypoxia decreased cell viability, occludin, and ZO-1 expression and increased tissue permeability, expression, and secretion of VEGF and PDGF. Axitinib significantly reduced hypoxia-induced effects on HUVEC and RPE cells. Our in vitro results suggest that axitinib may have promising properties as a potential treatment for diabetic macular edema.