Effect of COX inhibitors on VEGF-induced retinal vascular leakage and experimental corneal and choroidal neovascularization

Clinical Outcomes of Topical Bevacizumab for the Treatment of Corneal Neovascularization

Background and objective In corneal neovascularization, the peri-corneal vascular structure grows into a normally avascular cornea. This is due to an imbalance between the angiogenic and anti-angiogenic factors that sustain corneal transparency. There are various etiologies of this condition, and they can be divided into infective or non-infective causes, such as inflammation, trauma, or surgical causes. Corneal neovascularization has been shown to improve with the current treatments using steroids and anti-vascular endothelial growth factors. This study aimed to evaluate the effectiveness of topical bevacizumab as an anti-angiogenic agent in patients with corneal neovascularization. Methods This retrospective study included patients who suffered corneal neovascularization of various etiologies and completed six months of topical bevacizumab therapy between 2020 and 2022 at the Universiti Kebangsaan Malaysia Medical Centre. Results A total of 16 patients received treatment with topical bevacizumab over the three-year study period. Based on specified inclusion and exclusion criteria, 12 patients were eligible for inclusion in this study. Eight patients (66%) showed improvement in terms of either 'clock hours' of improvement, morphology, or regression of corneal neovascularization. All infective causes of corneal neovascularization showed improvement on completion of bevacizumab compared to other causes. Conclusion Topical bevacizumab can be one of the treatment choices for corneal neovascularization. As the outcome varies depending on the severity and chronicity of the condition, the attending ophthalmologist should treat each case differently. Although topical bevacizumab is more effective in mild and moderate cases, the indications for its use in chronic cases remain debatable as the results are unfavorable in such cases.

Topical application of TAK1 inhibitor encapsulated by gelatin particle alleviates corneal neovascularization

Rationale: Corneal neovascularization (CoNV) is a severe complication of various types of corneal diseases, that leads to permanent visual impairment. Current treatments for CoNV, such as steroids or anti-vascular endothelial growth factor agents, are argued over their therapeutic efficacy and adverse effects. Here, we demonstrate that transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) plays an important role in the pathogenesis of CoNV. Methods: Angiogenic activities were assessed in ex vivo and in vitro models subjected to TAK1 inhibition by 5Z-7-oxozeaenol, a selective inhibitor of TAK1. RNA-Seq was used to examine pathways that could be potentially affected by TAK1 inhibition. A gelatin-nanoparticles-encapsulated 5Z-7-oxozeaenol was developed as the eyedrop to treat CoNV in a rodent model. Results: We showed that 5Z-7-oxozeaenol reduced angiogenic processes through impeding cell proliferation. Transcriptome analysis suggested 5Z-7-oxozeaenol principally suppresses cell cycle and DNA replication, thereby restraining cell proliferation. In addition, inhibition of TAK1 by 5Z-7-oxozeaenol blocked TNFα-mediated NFκB signalling, and its downstream genes related to angiogenesis and inflammation. 5Z-7-oxozeaenol also ameliorated pro-angiogenic activity, including endothelial migration and tube formation. Furthermore, topical administration of the gelatin-nanoparticles-encapsulated 5Z-7-oxozeaenol led to significantly greater suppression of CoNV in a mouse model compared to the free form of 5Z-7-oxozeaenol, likely due to extended retention of 5Z-7-oxozeaenol in the cornea. Conclusion: Our study shows the potential of TAK1 as a therapeutic target for pathological angiogenesis, and the gelatin nanoparticle coupled with 5Z-7-oxozeaenol as a promising new eyedrop administration model in treatment of CoNV.

Deterioration of wound healing and intense suppression of MMP-9 mRNA expression after short-term administration of different topical glucocorticoids or NSAIDs in an avian model of corneal lesions

Background

Corneal lesions are considered among important ophthalmic conditions in avian patients. Short-term outcome of using anti-inflammatory agents in corneal lesions of birds are not well-described.

Aims

The study evaluates effects of different anti-inflammatory agents on healing of alkali burn-induced corneal lesions in layer hens as an avian model.

Methods

Adult layers were randomly allocated into 7 groups (n=15) as follows: 1. Negative (normal) control (NC), and 2. Positive control (PC) with an experimentally induced-corneal lesion, 3-7. Birds with corneal lesions that were treated with dexamethasone, fluorometholone, prednisolone, ketorolac, or diclofenac eye-drops every 6 hours (QID) for 5 consecutive days.

Results

At the end of the experiment, proper healing was observed in PC group based on lesion area, while treated groups showed statistically larger lesion sizes as compared to PC birds (P<0.05). Although no significant difference was observed among groups, birds treated with ketorolac, diclofenac or fluorometholone had higher histopathological scores for most of the assayed parameters than other groups. Levels of tumor necrosis factor-α (TNF-α) and vascular endothelial growth factor (VEGF) in corneal tissue of different groups were statistically the same. The mRNA expression of matrix metalloproteinase-9 (MMP-9) was increased 2.5 folds in PC group as compared to NC birds. However, birds treated with anti-inflammatory agents showed no detectable expression of MMP-9 mRNA.

Conclusion

Five days of topical administration of non-steroidal anti-inflammatory agents (NSAIDs) or glucocorticoids (GCs) is associated with suppression of MMP-9 mRNA expression in corneal tissue and detrimental effects on wound healing in layers with alkali burn-induced corneal ulcers.

Nonsteroidal anti-inflammatory drugs for retinal neurodegenerative diseases

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most common prescription drugs for inflammation, and topical NSAIDs are often used in ophthalmology to reduce pain, photophobia, inflammation, and edema. In recent years, many published reports have found that NSAIDs play an important role in the treatment of retinal neurodegenerative diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), glaucoma, pathological myopia, and retinitis pigmentosa (RP). The aim of the current review is to provide an overview of the role of various NSAIDs in the treatment of retinal neurodegenerative diseases and the corresponding mechanisms of action. This review highlighted that the topical application of NSAIDs for the treatment of retinal degenerative diseases has been studied to a remarkable extent and that its beneficial effects in many diseases have been proven. In the future, prospective studies with large study populations are required to extend these effects to clinical settings.

Prostaglandin E2 promotes pathological retinal neovascularisation via EP4R-EGFR-Gab1-AKT signaling pathway

Proliferative retinopathies, such as proliferative diabetic retinopathy (PDR) and retinopathy of prematurity (ROP) are major causes of visual impairment and blindness in industrialized countries. Prostaglandin E2 (PGE2) is implicated in cellular proliferation and migration via E-prostanoid receptor (EP4R). The aim of this study was to investigate the role of PGE2/EP4R signaling in the promotion of retinal neovascularisation. In a streptozotocin (STZ)-induced diabetic model and an oxygen-induced retinopathy (OIR) model, rats received an intravitreal injection of PGE2, cay10598 (an EP4R agonist) or AH23848 (an EP4R antagonist). Optical coherence tomography, retinal histology and biochemical markers were assessed. Treatment with PGE2 or cay10598 accelerated pathological retinal angiogenesis in STZ and OIR-induced rat retina, which was ameliorated in rats pretreated with AH23848. Serum VEGF-A was upregulated in the PGE2-treated diabetic rats vs non-treated diabetic rats and significantly downregulated in AH23848-treated diabetic rats. PGE2 or cay10598 treatment also significantly accelerated endothelial tip-cell formation in new-born rat retina. In addition, AH23848 treatment attenuated PGE2-or cay10598-induced proliferation and migration by repressing the EGF receptor (EGFR)/Growth factor receptor bound protein 2-associated binder protein 1 (Gab1)/Akt/NF-κB/VEGF-A signaling network in human retinal microvascular endothelial cells (hRMECs). PGE2/EP4R signaling network is thus a potential therapeutic target for pathological intraocular angiogenesis.

Pharmacological Potential of Small Molecules for Treating Corneal Neovascularization

Under healthy conditions, the cornea is an avascular structure which allows for transparency and optimal visual acuity. Its avascular nature is maintained by a balance of proangiogenic and antiangiogenic factors. An imbalance of these factors can result in abnormal blood vessel proliferation into the cornea. This corneal neovascularization (CoNV) can stem from a variety of insults including hypoxia and ocular surface inflammation caused by trauma, infection, chemical burns, and immunological diseases. CoNV threatens corneal transparency, resulting in permanent vision loss. Mainstay treatments of CoNV have partial efficacy and associated side effects, revealing the need for novel treatments. Numerous natural products and synthetic small molecules have shown potential in preclinical studies in vivo as antiangiogenic therapies for CoNV. Such small molecules include synthetic inhibitors of the vascular endothelial growth factor (VEGF) receptor and other tyrosine kinases, plus repurposed antimicrobials, as well as natural source-derived flavonoid and non-flavonoid phytochemicals, immunosuppressants, vitamins, and histone deacetylase inhibitors. They induce antiangiogenic and anti-inflammatory effects through inhibition of VEGF, NF-κB, and other growth factor receptor pathways. Here, we review the potential of small molecules, both synthetics and natural products, targeting these and other molecular mechanisms, as antiangiogenic agents in the treatment of CoNV.

Sex differences in corneal neovascularization in response to superficial corneal cautery in the rat

Sex-based differences in susceptibility have been reported for a number of neovascular ocular diseases. We quantified corneal neovascularization, induced by superficial silver nitrate cautery, in male and female inbred albino Sprague-Dawley, inbred albino Fischer 344, outbred pigmented Hooded Wistar and inbred pigmented Dark Agouti rats of a range of ages. Corneal neovascular area was quantified on haematoxylin-stained corneal flatmounts by image analysis. Pro-and anti-angiogenic gene expression was measured early in the neovascular response by quantitative real-time polymerase chain reaction. Androgen and estrogen receptor expression was assessed by immunohistochemistry. Male rats from all strains, with or without ocular pigmentation, exhibited significantly greater corneal neovascular area than females: Sprague-Dawley males 43±12% (n = 8), females 25±5% (n = 12), p = 0.001; Fischer 344 males 38±10% (n = 12) females 27±8% (n = 8) p = 0.043; Hooded Wistar males 32±6% (n = 8) females 22±5% (n = 12) p = 0.002; Dark Agouti males 37±11% (n = 9) females 26±7% (n = 9) p = 0.015. Corneal vascular endothelial cells expressed neither androgen nor estrogen receptor. The expression in cornea post-cautery of Cox-2, Vegf-a and Vegf-r2 was significantly higher in males compared with females and Vegf-r1 was significantly lower in the cornea of males compared to females, p<0.001 for each comparison. These data suggest that male corneas are primed for angiogenesis through a signalling nexus involving Cox-2, Vegf-a, and Vegf receptors 1 and 2. Our findings re-enforce that pre-clinical animal models of human diseases should account for sex-based differences in their design and highlight the need for well characterized and reproducible pre-clinical studies that include both male and female animals.

Prevention of corneal neovascularization by subconjunctival injection of avastin® loaded thermosensitive hydrogels in rabbit model

The antibody avastin® (Ava) has been clinically to treat various intraocular neovascular diseases, but suffering from the rapid clearance and short shelf-life of Ava in the requirement of frequent administration. In the present study, we reports the sustained release of Ava from a thermosensitive hydrogel based on poly(ethylene glycol)-poly(ɛ-caprolactone)-poly(ethylene glycol) (PECE) copolymer for the control of corneal neovascularization in rabbit model. Ava were physically mixed with PECE aqueous solution at 4 °C, and resulting Ava-PECE solution showed a sol-gel transition at physiological temperature (37 °C). In vitro release study indicated that Ava-PECE hydrogel provided a sustained release of Ava up to 28 days and the drug release behavior could be finely modulated by the change of PECE concentration. A single subconjunctival injection of PECE hydrogel hardly caused the change of intraocular pressure and corneal endothelial morphology during the entire study period. Intraocular pharmacokinetic analysis suggested that the Ava-PECE hydrogel provided a relatively higher Ava concentration in cornea over Ava solution up to 14 days. In addition, anti-angiogenic effects of the Ava-PECE hydrogel in a suture-induced corneal neovascularization rabbit model indicated that the Ava-PECE hydrogel treatment exhibited superior anti-angiogenic efficacy over Ava solution treatment by decreasing the area ratio of neovascularization on 17 days. Overall, the proposed Ava-PECE hydrogel acting a sustained drug delivery system might be a promising vehicle for the treatment of corneal neovascularization.

[Current treatments for corneal neovascularization]

The extension of blood vessels into the normally avascular stroma defines corneal neovascularization. Though this phenomenon, pathophysiological and clinical features are well characterized, therapeutic modalities have been hindered by a lack of safe, efficacious and non-controversial treatments. In this literature review, we focus on available therapeutic options in light of recent evidence provided by animal and clinical studies. First, this review will focus on pharmacological treatments that target angiogenesis. The low cost and market availability of bevacizumab make it the first anti-angiogenic therapy choice, and it has demonstrable efficacy in reducing corneal neovascularization when administered topically or subconjunctivally. However, novel anti-angiogenic molecules targeting the intracellular pathways of angiogenesis (siRNA, antisense oligonucleotides) provide a promising alternative. Laser therapy (direct photocoagulation or photo-dynamic therapy) and fine needle diathermy also find a place in the treatment of stabilized corneal neovascularization alone or in association with anti-angiogenic therapy. Additionally, ocular surface reconstruction using amniotic membrane graft or limbal stem cell transplantation is essential when corneal neovascularization is secondary to primary or acquired limbal deficiency.

Presumed primary ocular lymphangiosarcoma with metastasis in a miniature horse

A 7-year-old, 153.0-kg American Miniature mare presented for evaluation of keratoconjunctivitis of the right eye (OD). A superior palpebral conjunctival mass and stromal keratitis were diagnosed. The incisional biopsy diagnosis was a presumptive corneal hemangiosarcoma. Transpalpebral enucleation was performed, and histopathologic evaluation confirmed angiosarcoma of the conjunctiva, cornea, and extraocular muscles. The horse developed progressive epistaxis and orbital swelling following surgery. A systemic workup was performed 3 months after enucleation, revealing regrowth within the orbit and marked cranial cervical lymphomegaly, suggestive of metastasis. Humane euthanasia was performed, and necropsy confirmed a locally invasive periorbital tumor with metastasis to the submandibular tissue, submandibular lymph node, and thoracic inlet. Histopathologic evaluation of necropsy specimens revealed polygonal to spindle neoplastic cells lining neoplastic vascular channels lacking erythrocytes. Immunohistochemically, the neoplastic cells labeled strongly positive for PROX-1, vimentin, CD-31, VEGF, weakly positive for factor VIII-related antigen, and negative for collagen IV. Based on the clinical, histological, and immunohistochemical features of this tumor, a primary ocular lymphangiosarcoma with metastasis was diagnosed.

Ocular delivery of macromolecules

Biopharmaceuticals are making increasing impact on medicine, including treatment of indications in the eye. Macromolecular drugs are typically given by physician-administered invasive delivery methods, because non-invasive ocular delivery methods, such as eye drops, and systemic delivery, have low bioavailability and/or poor ocular targeting. There is a need to improve delivery of biopharmaceuticals to enable less-invasive delivery routes, less-frequent dosing through controlled-release drug delivery and improved drug targeting within the eye to increase efficacy and reduce side effects. This review discusses the barriers to drug delivery via various ophthalmic routes of administration in the context of macromolecule delivery and discusses efforts to develop controlled-release systems for delivery of biopharmaceuticals to the eye. The growing number of macromolecular therapies in the eye needs improved drug delivery methods that increase drug efficacy, safety and patient compliance.

Effect of topical epigallocatechin gallate on corneal neovascularization in rabbits

PURPOSE

The aim of this study was to evaluate the efficacy of topical application of epigallocatechin gallate (EGCG) for the treatment of corneal neovascularization in a rabbit model.

METHODS

Corneal neovascularization was induced in 12 rabbits by placing a black silk suture in the corneal stroma (24 eyes) for a week. After suturing, 1 randomly chosen eye of the 12 rabbits was treated with topical EGCG at 2 different concentrations: 0.01% (group 1) and 0.1% (group 2), whereas the contralateral eyes were treated with sterilized balanced salt solution as the control. All eye drops were applied for 2 weeks after suturing. The suture materials were removed from all eyes on day 7. The surface area of corneal neovascularization was measured and analyzed in all eyes on days 7 and 14. On day 14, all eyes were extracted to measure the concentrations of vascular endothelial growth factor (VEGF) messenger RNA and cyclooxygenase-2 (COX-2) protein.

RESULTS

The surface area of induced corneal neovascularization was significantly smaller only in group 2 compared with that of the control group on days 7 and 14 (P < 0.001). The change in surface area of corneal neovascularization after removal of the suture material was not significantly different between all 3 groups. VEGF messenger RNA levels were significantly lower in group 2 than in the control group (P < 0.001). The concentration of COX-2 was significantly lower in group 2 than in the control group (P = 0.043), but no significant difference was observed between group 1 and the control group.

CONCLUSIONS

Topical administration of EGCG effectively inhibits corneal neovascularization in rabbits. This inhibitory effect is probably related to the suppression of VEGF and COX-2 meditated angiogenesis.

Inhibitory effects of regorafenib, a multiple tyrosine kinase inhibitor, on corneal neovascularization

AIM

To evaluate the inhibitory effects of regorafenib (BAY 73-4506), a multikinase inhibitor, on corneal neovascularization (NV).

METHODS

Thirty adult male Sprague-Dawley rats weighing 250-300 g, were used. Corneal NV was induced by NaOH in the left eyes of each rat. Following the establishment of alkali burn, the animals were randomized into five groups according to topical treatment. Group 1 (n = 6) received 0.9% NaCl, Group 2 (n = 6) received dimethyl sulfoxide, Group 3 (n = 6) received regorafenib 1 mg/mL, Group 4 (n =6) received bevacizumab 5 mg/mL and Group 5 (n = 6) received 0.1% dexamethasone phosphate. On the 7d, the corneal surface covered with neovascular vessels was measured on photographs as the percentage of the cornea's total area using computer-imaging analysis. The corneas obtained from rats were semiquantitatively evaluated for caspase-3 and vascular endothelial growth factor by immunostaining.

RESULTS

A statistically significant difference in the percent area of corneal NV was found among the groups (P <0.001). Although the Group 5 had the smallest percent area of corneal NV, there was no difference among Groups 3, 4 and 5 (P >0.005). There was a statistically significant difference among the groups in apoptotic cell density (P = 0.002). The staining intensity of vascular endothelial growth factor in the epithelial and endothelial layers of cornea was significantly different among the groups (P <0.05). The staining intensity of epithelial and endothelial vascular endothelial growth factor was significantly weaker in Groups 3, 4 and 5 than in Groups 1 and 2.

CONCLUSION

Topical administration of regorafenib 1 mg/mL is partly effective for preventing alkali-induced corneal NV in rats.

Vascular endothelial growth factor modulates the function of the retinal pigment epithelium in vivo

PURPOSE

Retinal edema, the accumulation of extracellular fluid in the retina is usually attributed to inner blood retina barrier (BRB) leakage. Vascular endothelial growth factor plays an important role in this process. The effects of VEGF on the outer BRB, the RPE, however, have received limited attention. Here, we present a methodology to assess how VEGF modulates the integrity of the RPE barrier in vivo.

METHODS

Control subretinal blebs (1-5 μL) and blebs containing VEGF (1-100 μg/mL), placental growth factor (PlGF; 100 μg/mL), or albumin (100-1000 μg/mL) were injected into New Zealand White or Dutch Belted rabbits with IOP maintained at 10, 15, or 20 mm Hg. One-hour intravitreal pretreatment with ZM323881 (10 μM/L) was used to inhibit the VEGF response. Fluid resorption was followed by optical coherence tomography for 1 hour. Retinal pigment epithelium leakage was assessed by fluorescein angiography.

RESULTS

Increasing IOP resulted in an elevated rate of bleb resorption, while increasing albumin concentration in the bleb decreased the rate of resorption. Vascular endothelial growth factor, but not PlGF, caused a significant, concentration-dependent decrease in the rate of fluid resorption, which was reversed by ZM323881. Compared with albumin-filled blebs, VEGF-filled blebs showed accelerated early-phase leakage from the choroid.

CONCLUSIONS

Consistent with a localized modulation of RPE function, VEGF induced a significant reduction in fluid resorption and an increase in hydraulic conductivity. Our results establish VEGF as a major cytokine regulating RPE barrier properties in vivo and indicate that the RPE is a principal factor in the pathogenesis of retinal edema.

Preparation of naringenin/ β-cyclodextrin complex and its more potent alleviative effect on choroidal neovascularization in rats

Choroidal neovascularization (CNV) is characterized by abnormal blood vessels growing from the choroid. Current remedies for CNV have not shown favorable therapeutic efficacy. It is urgent to identify and develop more safe and potent anti-CNV agents via multiple technologies. We previously showed that the natural product naringenin attenuated CNV. However, naringenin has poor water solubility and low bioavailability. Here, we prepared the β-cyclodextrin (β-CD) complex of naringenin and characterized it using infrared spectra and X-ray diffraction analyses. Determination of content and solubility in the complex showed that naringenin accounted for 20.53% in the complex and its solubility was increased by more than 10-fold. Using a laser-induced CNV model in rats we demonstrated that naringenin/β-CD complex more significantly reduced CNV area than naringenin alone in rats. Furthermore, naringenin and its β-CD complex significantly inhibited the mRNA and protein expression of VEGF, COX-2, PI3K, p38MAPK, MMP-2, and MMP-9 in retina and choroid tissues. Naringenin/β-CD complex showed more significant inhibitory effect on VEGF and COX-2 expression than naringenin. These results collectively indicated that naringenin/β-CD complex could be a promising therapeutic option for CNV and that the beneficial effects could be linked to the anti-inflammatory properties of naringenin.

Progression of macular atrophy after PDT combined with the COX-2 inhibitor Nabumetone in the treatment of neovascular ARMD

AIM

To evaluate photodynamic therapy (PDT) combined with the preferential the cyclooxygenase-2 (COX-2) inhibitor, nabumetone in the treatment of the neovascular age-related macular degeneration (ARMD).

METHODS

A prospective, double-blind, randomized study on 60 patients with subfoveal CNV secondary to ARMD without any previous treatment. Patients were divided into a nabumetone or placebo group. The main endpoints were the change of best-corrected visual acuity (BCVA), central macular thickness (CRT) and number of required PDT treatments.

RESULTS

In the nabumetone group, 27 patients (90%) and 28 (93%) in the placebo group completed the follow-up of 12 months. In the nabumetone group, the mean CRT decreased from 332 μm (SD 68 μm) to 220 μm (SD 46 μm). In the placebo group, CRT decreased from 331 μm (SD 72 μm) to 254 μm (SD 61 μm). The mean BCVA was 0.68 log MAR (SD 0.22 log MAR) in the nabumetone group and 0.62 log MAR (SD 0.23 log MAR) in the placebo group at baseline. This stabilised in the placebo group to 0.66 log MAR (SD 0.33) but deteriorated in the nabumetone group to 0.86 log MAR (SD 0.41 log MAR). There was a significant reduction in the number of required PDTs in the nabumetone group, but significant progression of the RPE atrophy area.

CONCLUSION

Combined PDT with oral intake of the COX-2 inhibitor, nabumetone reduced the number of required PDT retreatments, but worsening BCVA caused by macular atrophy progression. Therefore the combination of the PDT with the nabumetone is not recommended.

Treatments for corneal neovascularization: a review

Corneal neovascularization (CNV) may be a physiological response to various stimuli, but a chronic and persistent upregulation of neoangiogenesis can result in pathological CNV. Pathological blood vessels are immature and lack structural integrity, predisposing the cornea to lipid exudation, inflammation, and scarring. CNV can therefore become a potentially blinding condition. In this review, we frame CNV in an epidemiological perspective, consider risk factors for CNV, provide an overview of CNV pathogenesis, and consider the impact of CNV on corneal transplantation. We consider treatments that are of largely historical interest, before reviewing contemporary medical and surgical treatments. Within medical treatments, we report on steroids, nonsteroidal anti-inflammatory agents, antivascular endothelial growth factor agents, and cyclosporine. Within surgical treatments, we report on the use of lasers, photodynamic therapy, superficial keratectomy, and diathermy/cautery-based treatments.

Inhibitory effects of SU5416, a selective vascular endothelial growth factor receptor tyrosine kinase inhibitor, on experimental corneal neovascularization

PURPOSE

Treatment of neovascularization in ocular diseases with vascular endothelial growth factor (VEGF) inhibition shows promising results. SU5416 is a low-molecular-weight tyrosine kinase inhibitor. It selectively inhibits the membrane-bound tyrosine kinase activity of VEGF-2 receptor (Flk-1/KDR) and blocks the intracellular signaling process. The aim of this study was to evaluate the effect of SU5416 on corneal neovascularization.

METHODS

Corneas were cauterized with silver nitrate/potassium nitrate sticks in 20 eyes of 20 BALB/C mice. In the study group (n = 10), SU5416 (25 mg/kg) dissolved in dimethyl sulfoxide was given as an intraperitoneal injection in a single daily dose for 7 days. The other group of 10 mice given intraperitoneal dimethyl sulfoxide alone served as a control group. After 7 days, corneal neovascularization was evaluated using photographs captured by fluorescein angiography. Colored photographs were taken by a biomicroscope with a digital camera. Data were expressed as mean neovascular length and mean number of new vessels for each animal. The values were computed and compared between the groups.

RESULTS

The mean burn stimulus intensities were not different between the groups. In the study group, the mean length of the vessels and the mean number of vessels were 0.49 ± 0.05 and 11.20 ± 1.69 mm, respectively. In the control group, the mean length of the vessels and the mean number of the vessels were 0.89 ± 0.11 and 17.80 ± 1.03 mm, respectively. There is a statistically significant difference in the mean length and the mean number of new vessels between the study and control groups (p < 0.001).

CONCLUSION

Selective inhibition of VEGFR-2 (Flk-1/KDR) tyrosine kinase with SU5416 was shown to have an inhibitory effect on corneal neovascularization in this animal model. VEGFR-2 (Flk-1/KDR) tyrosine kinase inhibition may represent a different pathway for treatment of the neovascularization process in ocular pathologies. Fluorescein angiography photographs of new vessels on the cornea may provide a better evaluation of neovascularization than colored images in animal models.

Improved assessment of laser-induced choroidal neovascularization

The primary objective of this study was to develop and evaluate new methods of analyzing laser-induced choroidal neovascularization (CNV), in order to make recommendations for improving the reporting of experimental CNV in the literature. Six laser burns of sufficient power to rupture Bruch's membrane were concentrically placed in each eye of 18 adult Norway rats. Eyes received intravitreal injections of either triamcinolone acetonide, ketorolac, or balanced salt solution (BSS). Fluorescein angiography (FA) was performed 2 and 3 weeks after injection, followed by choroidal flat mount preparation. Vascular leakage on FAs and vascular budding on choroidal mounts were quantified by measuring either the cross-sectional area of each CNV lesion contained within the best-fitting polygon using Adobe Photoshop (Lasso Technique or Quick Selection Technique), or the area of bright pixels within a lesion using Image-Pro Plus. On choroidal mounts, the Lasso Technique and Image-Pro Plus detected a significant difference in lesion size between either ketorolac or triamcinolone when compared to BSS, while the Quick Selection Technique did not (Lasso Technique, 0.78 and 0.64; Image-Pro Plus, 0.77 and 0.65). On FA, the Lasso Technique and Quick Selection Technique detected a significant difference in lesion size between either ketorolac or triamcinolone when compared to BSS, while Image-Pro Plus did not (Lasso Tool, 0.81 and 0.54; Quick Selection Tool, 0.76 and 0.57). Choroidal mounts and FA are both valuable for imaging experimental CNV. Adobe Photoshop and Image-Pro Plus are both able to detect subtle differences in CNV lesion size, when images are not manipulated. The combination of choroidal mounts and FA provides a more comprehensive assessment of CNV anatomy and physiology.

Subconjunctival bevacizumab for corneal neovascularization

PURPOSE

This work aimed to study and evaluate the effect of subconjunctival bevacizumab injection in patients with corneal neovascularization (CNV) resulting from different ocular surface disorders.

METHODS

Ten eyes with CNV caused by different ocular surface disorders were studied. All eyes had both major and minor vessel CNV caused by factors such as healed corneal ulcers, long-standing chronic inflammatory diseases and corneal ischaemia (caused by contact lenses). All eyes received a single subconjunctival injection of 2.5mg (0.1ml) bevacizumab. Morphological changes in the major and minor vessels were evaluated using slit-lamp biomicroscopy and corneal photography.

RESULTS

Conspicuous recession of the minor vessels of CNV was observed in all eyes at 2 weeks post-injection. The extent of CNV of the major vessels was significantly decreased at 2 weeks post-injection. The level of CNV continued to decrease noticeably for 3 months and then stabilized for the remainder of the 6-month follow-up period. Parameters used for evaluation included the total area of CNV, which amounted to 14.0 ± 5.4% of the corneal surface pre-injection, compared with 9.4 ± 3.9% post-injection (p < 0.01), reflecting a mean decrease in CNV of 33 ± 8%, and the extent of neovascularization, which decreased from 4.3 ± 1.5 clock hours pre-injection to 2.4 ± 1.1 clock hours post-injection (p <0.01). During the 6-month follow-up, none of the 10 eyes showed any complication that could be related to subconjunctival bevacizumab injection.

CONCLUSIONS

Bevacizumab can be used safely and effectively for CNV resulting from different ocular surface disorders. It represents an effective treatment for minor vessel neovascularization caused by long-standing chronic inflammation (e.g. trachoma) or long-standing corneal ischaemia (e.g. contact lenses), as well as for major vessel neovascularization resulting from different causes. Bevacizumab was well tolerated over the 6-month follow-up period.

(-)-Epigallocatechin 3-gallate (EGCG) at the ocular surface inhibits corneal neovascularization

Corneal neovascularization is often accompanied by inflammatory response and loss of their immune privilege which leads to significant visual impairment and worsens the prognosis of a subsequent penetrating keratoplasty. Several types of treatment are currently used. However, there are some associated limitations and complications. The consumption of (-)-epigallocatechin 3-gallate (EGCG) has been studied extensively as a potential treatment for a variety of carcinogenic and degenerative diseases due to its ability to suppress a variety of inflammatory and angiogenic factors such as NF-κB, IL-1β, COX2, VEGF, and matrix metalloproteinases. These factors are involved in the development of corneal neovascularization. The safety of long-term EGCG administration as well as the drug's high solubility in water urge further investigation of the therapeutic potential of this drug. Therefore, we propose that the administration of EGCG to the ocular surface represents a new chemopreventive alternative to suppress the corneal neovascularization induced by inflammation.

Genetic deletion of COX-2 diminishes VEGF production in mouse retinal Müller cells

Non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit COX activity, reduce the production of retinal VEGF and neovascularization in relevant models of ocular disease. We hypothesized that COX-2 mediates VEGF production in retinal Müller cells, one of its primary sources in retinal neovascular disease. The purpose of this study was to determine the role of COX-2 and its products in VEGF expression and secretion. These studies have more clearly defined the role of COX-2 and COX-2-derived prostanoids in retinal angiogenesis. Müller cells derived from wild-type and COX-2 null mice were exposed to hypoxia for 0-24 h. COX-2 protein and activity were assessed by western blot analysis and GC-MS, respectively. VEGF production was assessed by ELISA. Wild-type mouse Müller cells were treated with vehicle (0.1% DMSO), 10 microM PGE(2), or PGE(2) + 5 microM H-89 (a PKA inhibitor), for 12 h. VEGF production was assessed by ELISA. Hypoxia significantly increased COX-2 protein (p < 0.05) and activity (p < 0.05), and VEGF production (p < 0.0003). COX-2 null Müller cells produced significantly less VEGF in response to hypoxia (p < 0.05). Of the prostanoids, PGE(2) was significantly increased by hypoxia (p < 0.02). Exogenous PGE(2) significantly increased VEGF production by Müller cells (p < 0.0039), and this effect was inhibited by H-89 (p < 0.055). These data demonstrate that hypoxia induces COX-2, prostanoid production, and VEGF synthesis in Müller cells, and that VEGF production is at least partially COX-2-dependent. Our study suggests that PGE(2), signaling through the EP(2) and/or EP(4) receptor and PKA, mediates the VEGF response of Müller cells.

The cornea of Guinea pig: structural and functional studies

OBJECTIVE

To describe the functional and structural characteristics of the cornea in healthy Guinea pigs.

ANIMALS STUDIED

Healthy male and female pigmented and albino Guinea pigs (Caviaporcellus) aged 3-5 months old were used.

PROCEDURES

The animals' corneas underwent different in vivo studies including: slit-lamp biomicroscopy, fluorescein staining (FS), break-up time test (BUT), confocal microscopy and pachymetry. The corneas were also studied histopathologically with light microscopy, immunohistochemistry and transmission electron microscopy.

RESULTS

No significant differences were found between pigmented and albino animals, male and female, OD and OS in any study performed. The differences on corneal thickness values were not significant among central (227.85 +/- 14.09 microm) and upper and temporal peripheral regions (226.60 +/- 12.50 and 225.70 +/- 14.40 microm, respectively). All histological studies performed permitted identification and precise description of the different corneal structures in Guinea pigs: the stratified epithelium (45.52 +/- 5.26 microm), Bowman's layer (2.23 +/- 0.38 microm), stroma (163.69 +/- 4.90 microm), Descemet's membrane (3.96 +/- 0.46 microm) and the endothelium (5.09 +/- 0.71 microm). Combining results from all eyes mean and SD from corneal BUT values was 4.98 +/- 1.67 s. Corneas often showed discrete superficial erosions being the FS positive in both eyes from all the animals.

CONCLUSION

This study provides a detailed in vivo and postfixed histological description of the Guinea pig's cornea and information about the physiological tests.

Role of cytosolic phospholipase A(2) in retinal neovascularization

PURPOSE

To identify and characterize the role of cytosolic phospholipase A(2) (cPLA(2)) in retinal angiogenesis using relevant cell-based assays and a rodent model of retinopathy of prematurity.

METHODS

The phosphorylation states of cPLA(2) and p38 MAP kinase and the expression of COX-2 were assessed by Western blot analysis in rat Müller cells. The activities of PLA(2) enzymes in rat retinal lysates were assessed using a commercially available assay. Prostaglandin E(2) (PGE(2)) and VEGF levels in Müller cell-conditioned medium and in retinal tissue samples were measured by ELISA. Rat retinal microvascular endothelial cell proliferation was measured using a BrdU assay. Efficacy of the cPLA(2) inhibitor CAY10502 was tested using the rat model of oxygen-induced retinopathy (OIR) in which neovascularization (NV) was assessed by computer-assisted image analysis.

RESULTS

In Müller cells, hypoxia increased the phosphorylation of cPLA(2) and p38 MAP kinase by 4-fold and 3-fold respectively. The cPLA(2) inhibitor CAY10502 decreased hypoxia-induced PGE(2) and VEGF levels in Müller cell-conditioned medium by 68.6% (P < 0.001) and 46.6% (P < 0.001), respectively. Retinal cPLA(2) activity peaked 1 day after oxygen exposure in OIR rats. CAY10502 (250 nM) decreased OIR-induced retinal PGE(2) and VEGF levels by 69% (P < 0.001) and 40.2% (P < 0.01), respectively. Intravitreal injection of 100 nM CAY10502 decreased retinal NV by 53.1% (P < 0.0001).

CONCLUSIONS

cPLA(2) liberates arachidonic acid, the substrate for prostaglandin (PG) production by the cyclooxygenase enzymes. PGs can exert a proangiogenic influence by inducing VEGF production and by stimulating angiogenic behaviors in vascular endothelial cells. Inhibition of cPLA(2) inhibits the production of proangiogenic PGs. Thus, cPLA(2) inhibition has a significant influence on pathologic retinal angiogenesis.

Pathophysiology of cyclooxygenase inhibition in animal models

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid into prostaglandins (PGs), which play a significant role in health and disease in the gastrointestinal tract (GI) and in the renal, skeletal, and ocular systems. COX-1 is constitutively expressed and found in most normal tissues, whereas COX-2 can be expressed at low levels in normal tissues and is highly induced by pro-inflammatory mediators. Inhibitors of COX activity include: (1) conventional nonselective, nonsteroidal anti-inflammatory drugs (ns-NSAIDs) and (2) COX-2 selective nonsteroidal anti-inflammatory drugs (COX-2 s-NSAIDs). Inhibition of COX-1 often elicits GI toxicity in animals and humans. Therefore, COX-2 s-NSAIDs were developed to provide a selective COX-2 agent, while minimizing the attendant COX-1-mediated GI toxicities. Rats and dogs overpredict COX inhibition for renal effects such as renal handling of electrolytes in humans. COX inhibitors are shown to have both beneficial and detrimental effects, such as on healing of ligament or tendon tears, on the skeletal system in animal models. Certain ophthalmic conditions such as glaucoma and keratitis are associated with increased COX-2 expression, suggesting a potential role in their pathophysiology.

Strategies for blocking angiogenesis in diabetic retinopathy: from basic science to clinical practice

Proliferative diabetic retinopathy (PDR) demands both more effective and less expensive biologically based treatments. Our understanding of the pathophysiology of the disease is increasing as new biochemical pathways are identified. Most reports emphasize proangiogenic stimuli, with the natural inhibitory elements receiving little attention. There are two therapeutic strategies for blocking retinal angiogenesis in PDR: systemic drug administration (protein kinase C inhibitors and somatostatin analogs) or local therapies (anti-vascular endothelial growth factor strategies, anti-inflammatory agents, gene therapy and stem cell therapy). This review mainly focuses on the role of local therapies, especially intravitreous delivery, in the management of PDR. The potential for adverse effect are also discussed. The availability of these new strategies or the combination of them will not only be beneficial in treating PDR but may also result in a shift towards treating earlier stages of diabetic retinopathy, thus easing the burden of this devastating disease.

The effects of the subconjunctival injection of bevacizumab (Avastin®) on angiogenesis in the rat cornea

The purpose of this study was to evaluate the effects of the use of the subconjunctival injection of bevacizumab (Avastin®) on angiogenesis in the rat cornea. Corneas of 20 Wistar male rats were cauterized with silver nitrate crystal. Animals were divided in four groups: control group (GC) that received subconjunctivally 0.02 ml of 0.9% saline solution on the day of the lesion; group GO that received subconjunctivally 0.02 ml of bevacizumab just after the lesion; group G3 that received bevacizumab on day 3 and group G5 that received bevacizumab on day 5 after lesion. Animals were euthanized on day 7. The newly formed vessels were quantified after China Ink perfusion and photographs were obtained and analyzed in a computerized system (Image Pro-Plus®). In the control group, neovascularization covered 53.56% ± 15.11 (mean ± SD) of the corneal surface, compared with 35.57% ± 18.80 (mean ± SD) in the G0 group, 30.60%±11.82 (mean±SD) in the G3 and 35.86%±0.07 (mean±SD) in the G5. The results showed an inhibition of angiogenesis when the control group was compared with all treated groups. These results suggest that subconjunctival injection of bevacizumab is able to inhibit corneal angiogenesis independently of the day of treatment.

Modulation of corneal vascularization

Avascularity of normal cornea is a result of homeostasis between anti-angiogenic and pro-angiogenic stimuli. Disruption of this delicate balance during corneal wound healing can lead to pathological corneal vascularization. Several unique characteristics in the ocular surface epithelia modulate corneal avascularity. Normal cornea contains heparan sulfate to prevent the release of potent angiogenic cytokines, such as basic fibroblast growth factor (bFGF) from the Bowman's layer. Potent angiostatic factors, such as endostatin and angiostatin, can be produced from degradation of corneal extracelluar matrix. In contrast, conjunctiva contains angiogenic cytokines, such as bFGF and vascular endothelial growth factor. In addition to regulating release of angiogenic and angiostatic cytokines, matrix metalloproteinases (MMPs) and other proteolytic enzymes can modulate corneal vascularization via matrix degradation to allow endothelial migration and tissue remodeling. When the cornea becomes vascularized, inflammatory cells and mediators gain uninhibited access to the cornea, thus rendering immune sensitization and increased risk of corneal graft rejection. Novel therapies targeting angiogenic cytokines or MMPs have been shown to suppress corneal vascularization effectively in animal models, and may have therapeutic potential for clinical use.

Emmetropization and schematic eye models in developing pigmented guinea pigs

A model of the axial change in ocular parameters of the guinea pig eye from 2 to 825 days of age was developed and a corresponding paraxial schematic eye model applicable from 2 to 100 days of age was constructed. Axial distances increased logarithmically over time except for the lens in which growth was more complex. Over the first 30 days, ocular elongation was approximately linear: ocular length increased by 37 microm/day, the majority due lens expansion. The choroid and sclera thickened with age, while the retina thinned in proportion to the increased ocular size, and the model suggests that there is no small eye artefact for white light retinoscopy. Refractive error just after birth was +4.8D but halved within the first week. Emmetropization occurred within the first month of life similar to that in other species when aligned at the point of sexual maturity and scaled by the time taken to reach adulthood. The power of the eye was 227D at 2 days of age and reduced by 19.7D by 100 days due to a 22% decrease in the power of the cornea. The posterior nodal distance (PND) was 4.7 mm at 30 days of age, with a maximum rate of change of 13 microm/day during the first week. The ratio of PND to axial length declined until at least 100 days of age, well after emmetropia was reached. This suggests that the maintenance of emmetropia is not sustained through proportional axial growth, but involves some active mechanism beyond simple scaling. The model predicts that 1D of myopia requires an elongation of between 23 and 32 microm, depending upon age, suggesting that a resolution of at least 50 microm is required in methods used to determine the significance of ocular length changes in guinea pig models of refractive development. Retinal magnification averaged 80 microm/degree, and the maximum potential brightness of the retinal image was high, which together with a ratio of lens power to corneal power of 1.7-2.0 suggests that the guinea pig eye is adapted for nocturnal conditions.

Unique Homologous siRNA Blocks Hypoxia-Induced VEGF Upregulation in Human Corneal Cells and Inhibits and Regresses Murine Corneal Neovascularization

PURPOSE

To evaluate the results of amniotic membrane transplantation (AMT) for ocular surface reconstruction in chemical and thermal injuries.

METHODS

Retrospective review of case records of patients who had undergone AMT for chemical injuries (January 1998 to May 2001).

RESULTS

Seventy two eyes of 69 patients were studied of which 24 were acute cases (median-2 days, range, 1-20 days) and 48 were chronic cases (median-12.4 months, range, 1.02-95.8 months). Mean age was 22.4 years (SD +/- 13.34 years) and average follow up duration was 7.8 months (SD +/- 7.1). Main clinical findings were symblephara (52.8%), corneal vascularization (51.3%), conjunctivalization (45.8%), Limbal ischemia (45.8%), Limbal stem cell deficiency (55.5%) and epithelial defect (48.6%). 18 cases were due to acid injuries (5 acute, 13 chronic), 52 were due to alkali (18 acute and 34 chronic) and 2 cases were due to thermal burns (1 each acute and chronic). Overall success rate was 87.5% in acute cases and 72.9% in chronic cases. Indication-wise success rates were 94.3% for epithelial defect healing, 88.2% for symptomatic relief, 59.7% for ocular surface reconstruction, and 55% for improving limbal stem cell function. Success was not achieved in any outcome measure in 1/24 (4.2%) in acute group and 6/48 (12.5%) in chronic group.

CONCLUSION

AMT helps in ocular surface reconstruction, promotes rapid epithelial healing and partially restores limbal stem cell function. It can be considered as an effective modality for the ocular surface restoration in chemical and thermal injuries in selected cases. Success rates in acute and chronic cases are comparable.

Induced angiogenesis under cerebral ischemia by cyclooxygenase 2 and hypoxia-inducible factor naked DNA in a rat indirect-bypass model

We recently reported that hypoxic stress induces the expression of HIF-1alpha, HIF-2alpha, cyclooxygenases-2 (COX-2) and VEGF in vivo. In this study, we investigated whether HIF-1alpha, HIF-2alpha, or COX-2 naked DNA induced angiogenesis in a cerebral ischemic model in vivo. We utilized a rat encephalo-myo-synangiosis (EMS) model and inoculated naked DNA into the brain surface. We analyzed whether DNA induced angiogenic factors and neovascularization. New blood vessel formation was detected by anti-Factor VIII staining. A histological section treated with HIF-2alpha or COX-2 DNA showed an increased expression of VEGF with angiogenesis, in comparison to the control DNA. The HIF-1alpha, HIF-2alpha, and COX-2 are able to promote significant angiogenesis development. These results suggest the feasibility of a novel approach for therapeutic angiogenesis of cerebral ischemia in which neovascularization may be indirectly achieved using a transcriptional and cytokine's regulatory strategy.

A2E selectively induces cox-2 in ARPE-19 and human neural cells

PURPOSE

To investigate the expression of cyclooxygenase (COX)-1, -2, and -3 RNA and protein in retinal pigment epithelial (ARPE-19) cells and in human neural (HN) cells exposed to the stress-inducing cytokines IL-1beta and TNF-a, the oxidizing peroxide H(2)O(2), the combination of TNF-alpha + H(2)O(2), and the lipofuscin fluorophore A2E.

METHODS

Three-week-old ARPE-19 and HN cells were incubated with IL-1beta (10 ng/ml), TNF-alpha (10 ng/ml), H(2)O(2) (0.6 microM), TNF-alpha + H(2)O(2) (10 ng/ml and 0.6 microM), or A2E (10 microM) for 8 hr, after which total RNA and whole cellular proteins were isolated. Cyclooxygenase-1, -2, and -3 RNA and protein levels were quantified using Northern and Western immunoassay.

RESULTS

IL-1beta-, H(2)O(2)-, TNF-alpha-, TNF-alpha + H(2)O(2)-, or A2E-stressed ARPE-19 or HN cells displayed no significant upregulation in COX-1 or COX-3 RNA message abundance; however, significant upregulation was observed in COX-2 RNA message and protein abundance. A2E treatment of HN cells resulted in modest increases in COX-3 protein, an effect that was not observed in ARPE-19 cells.

CONCLUSIONS

COX-2 RNA levels were induced in cytokine-, peroxide-, and A2E-stressed ARPE-19 and HN cells. Lack of induction of COX-3 RNA message by A2E, coupled with increases in COX-3 protein under identical treatment conditions, suggest that significant post-transcriptional or post-translational controls may regulate COX-3 gene expression in HN cells. Stress-induced upregulation of COX-2 gene expression in ARPE-19 and HN cells may play a mechanistic role in promoting proinflammatory and/or pro-oxidative pathology in these tissues.

Cyclooxygenase inhibition in early onset of tumor growth and related angiogenesis evaluated in EP1 and EP3 knockout tumor-bearing mice

It is well established that prostanoids are essential for local inflammation including cell proliferation and apoptosis. Accordingly, prostaglandin E2 (PGE(2)) is a critical factor in wound healing, tumor invasiveness and progression. Therefore, the aim of the present work was to evaluate effects by PGE(2) on tumor vascular density at early onset of tumor growth where hypoxia is limited. Wild-type mice (C57Bl, C3H/HeN) bearing either MCG-101 tumors or a malignant melanoma (K1735-M2) with either high or insignificant PGE(2) production and subsequently different in sensitivity to cyclooxygenase (COX) inhibition were used. Tumor angiogenesis was estimated by intravital microscopy and immune histochemical analysis in wild type and EP(1) or EP(3) subtype receptor knockout mice (C57Bl). Both MCG-101 and K1735-M2 tumor cells stimulated early outgrowth of tumor vessels in proportion to intrinsic growth rate of tumor cells. Indomethacin had no effects on tumor growth or tumor related vascular area in K1735-M2 bearing mice. By contrast, indomethacin decreased tumor cell proliferation and increased apoptosis in MCG-101 tumors with subsequent adaptation in tumor vascular density. Effects of indomethacin on early growth of MCG-101 tumors were not related to tumor content of bFGF protein, while our earlier studies on long-term tumor growth have shown decreased mRNA levels of bFGF during indomethacin treatment. Early onset of tumor growth was significantly promoted in EP(3)- but not in EP(1)-knockouts, although long-term tumor growth is attenuated in EP(1)-knockouts as reported elsewhere. Our results demonstrate that tumor production of PGE(2) promotes primarily net growth of tumor cells with subsequent adaptations in development of the tumor vasculature. Therefore, it is likely that angiogenesis is not a limiting step at the early onset of tumor growth.

Rationale for combination therapies for choroidal neovascularization

PURPOSE

To provide a conceptual framework for the development and use of combination therapies for choroidal neovascularization secondary to age-related macular degeneration.

DESIGN

Literature review, integration of data, and creation of hypothesis.

METHODS

An assessment of angiogenesis, cancer therapy, and inflammation was performed as they may pertain to choroidal neovascularization. A conceptual framework was created in which therapies for choroidal neovascularization could be evaluated alone or in combination.

RESULTS

Angiogenesis occurs because cells produce angiogenic stimuli to encourage blood vessels to develop. This growth of vessels involves an orchestrated interaction among many mediators offering opportunity to modulate or inhibit the entire process. A two-component model for choroidal neovascularization is proposed. The vascular component of choroidal neovascularization is comprised of vascular endothelial cells, endothelial cell precursors, and pericytes. The extravascular component, which by histopathology appears to be both the source of angiogenic stimuli and often the largest component volumetrically, is comprised of inflammatory, glial and retinal pigment epithelial cells, and fibroblasts. Tissue damage can be caused by either component. Each component can be targeted through as variety of monotherapies. Combination therapies offer the possibility of attacking one component in more than one way or by attacking both components simultaneously.

CONCLUSIONS

The two-component model of choroidal neovascularization can be used to evaluate the mechanism of action and possible interactions of these agents in a conceptual framework. Extension of these ideas can help guide development of new treatment agents and approaches.

Zystoides Makulaödem bei Uveitis

Cystoid macular edema (CME) is the most frequent cause of visual deterioration in uveitis patients. Intraocular inflammation disturbs the blood-retina barrier and leads to retinal edema. The basis of successful treatment is the anti-inflammatory and immunosuppressive therapy of uveitis. Restoration of the blood-retina barrier is mediated by corticosteroids and nonsteroidal anti-inflammatory agents. Resorption of extracellular fluid is improved by systemic carboanhydrase inhibitors. Despite aggressive therapy loss of visual acuity is frequent. Therefore, early diagnosis of CME and initiation of treatment, even if visual acuity is not yet impeded, is mandatory.

Corticosteroids inhibit VEGF-induced vascular leakage in a rabbit model of blood-retinal and blood-aqueous barrier breakdown

PURPOSE

Recent clinical studies show that a single intravitreal injection of the corticosteroid triamcinolone acetonide (TAA) may reduce edematous retinal swelling and improve visual acuity in patients with diabetic macular edema (DME). In addition, clinical and experimental studies strongly suggest that blood-retinal barrier breakdown in diabetes is induced by vascular endothelial growth factor (VEGF). These results suggest that corticosteroids may modulate VEGF-mediated responses in vivo. To test this hypothesis directly, the current study evaluated the effects of TAA and dexamethasone (DEX) in a newly developed rabbit model of VEGF-induced blood-retinal barrier and blood-aqueous (iris) barrier breakdown.

METHODS

VEGF165 or vehicle was injected intravitreally in female Dutch Belt rabbits, and scanning ocular fluorophotometry was used to non-invasively measure fluorescein leakage from retinal and iris vasculature. VEGF-induced retinal vasculopathy was further assessed with fundus imaging, fluorescein angiography, and ocular coherence tomography. For pharmacologic studies, rabbits were treated with either DEX (2 mg kg(-1) daily, s.c.), TAA (2 or 4 mg, intravitreal), indomethacin (20 mg kg(-1) daily, s.c.), or vehicle (s.c. or intravitreal). Human umbilical vein endothelial cells (HUVEC) were loaded with the fluorescent Ca2+ indicator dye fluo-4 and treated with dexamethasone (0.1-10 microM) or vehicle for either 2 or 24 hr prior to stimulation with 10 ng ml(-1) VEGF165.

RESULTS

VEGF injected intravitreally induced a time and dose-dependent breakdown of the blood-retinal and blood-aqueous barriers. Maximal vascular leakage was measured at 48 hr after intravitreal injection with a dose of 500 ng VEGF. Other effects of VEGF included prominent retinal vasodilation, vessel tortuousity, fluorescein leakage from retinal vessels, and inner retinal edema. These VEGF-mediated responses are transient and approach baseline by 1 week. VEGF-induced blood-retinal and blood-aqueous barrier breakdown was completely blocked by the corticosteroid DEX administered systemically for 3 days. In contrast, the non-steroidal anti-inflammatory drug, indomethacin, had no effect. In a separate study with VEGF injected intravitreally at six different time points over 5 months, a single intravitreal 2 mg dose of TAA completely blocked VEGF-induced retinal and iris leakage for 45 days. VEGF/VEGF receptor-2-mediated Ca2+ mobilization in endothelial cells was not affected by 2 or 24 hr pretreatment with dexamethasone.

CONCLUSION

These results indicate that one mechanism by which corticosteroids block blood-ocular barrier breakdown and edema is via their modulation of signaling or effector proteins downstream of the VEGF receptor.