The role of vascular endothelial growth factor (VEGF) in abnormal vascular changes in the adult rat eye

Suppression of choroidal neovascularization by Endostar in rats

Choroidal neovascularization (CNV) is common in various retinal and choroidal diseases, and may result in severe and irreversible loss of vision. Our previous studies suggested that Endostar, a novel recombinant endostatin, is able to inhibit the proliferation and migration of choroid‑retinal endothelial cells. To further evaluate the effect of Endostar on the formation of CNV in vivo, a rat model of laser‑induced CNV was constructed and Endostar or phosphate‑buffered saline treatment was administered intravitreally every other day. Using fluorescein angiography (FA), reduced CNV incidence and leakage grade was observed in the Endostar group. In addition, CNV area and maximal thickness were prominently reduced in the Endostar group measured by choroid flat mounts and sections. Furthermore, vascular endothelial growth factor (VEGF), hypoxia‑inducible factor 1α and chemokine C‑X‑C motif ligand 1 were markedly reduced in the Endostar group as determined by quantitative polymerase chain reaction and downregulation of VEGF was also verified by western blot analysis at the protein level. This study demonstrates that Endostar suppressed CNV in a rat model, which may be largely mediated by the downregulation of VEGF and other angiogenic molecules.

Effect of cediranib, an inhibitor of vascular endothelial growth factor receptor tyrosine kinase, in a mouse model of choroidal neovascularization

BACKGROUND

This study was conducted to evaluate the effect of cediranib, an inhibitor of vascular endothelial growth factor receptor tyrosine kinase, in a mouse model of laser-induced choroidal neovascularization.

METHODS

Choroidal neovascularization was induced in C57BL/6 mice by rupturing Bruch's membrane using laser photocoagulation. Following laser injury, the mice were divided into three groups and administered either vehicle, 1 mg/kg or 5 mg/kg of cediranib daily by oral gavage for 2 weeks. Two weeks after laser injury, the area of choroidal neovascularization lesions was measured by choroidal flat mounts using fluorescein-labelled dextran. Immunofluorescence staining with isolectin IB4 was also used to quantify the choroidal neovascularization lesions.

RESULTS

Choroidal flat mount analysis revealed that orally administered cediranib reduced the extent of choroidal neovascularization. The groups treated with 1 and 5 mg/kg/day showed 57.2 and 66.0% reduction of choroidal neovascularization lesions, respectively, compared with the control group treated with vehicle alone (P = 0.012). The size of the fluorescently labelled choroidal neovascularization complex in cediranib-treated groups was much smaller than that from vehicle-treated group (P = 0.035).

CONCLUSIONS

Cediranib inhibited laser-induced choroidal neovascularization in mice and may have therapeutic potential for patients with neovascular age-related macular degeneration.

Of mice and not humans: how reliable are animal models for evaluation of herpes CD8(+)-T cell-epitopes-based immunotherapeutic vaccine candidates?

Herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2)-specific CD8(+) T cells that reside in sensory ganglia, appear to control recurrent herpetic disease by aborting or reducing spontaneous and sporadic reactivations of latent virus. A reliable animal model is the ultimate key factor to test the efficacy of therapeutic vaccines that boost the level and the quality of sensory ganglia-resident CD8(+) T cells against spontaneous herpes reactivation from sensory neurons, yet its relevance has been often overlooked. Herpes vaccinologists are hesitant about using mouse as a model in pre-clinical development of therapeutic vaccines because they do not adequately mimic spontaneous viral shedding or recurrent symptomatic diseases, as occurs in human. Alternatives to mouse models are rabbits and guinea pigs in which reactivation arise spontaneously with clinical herpetic features relevant to human disease. However, while rabbits and guinea pigs develop spontaneous HSV reactivation and recurrent ocular and genital disease none of them can mount CD8(+) T cell responses specific to Human Leukocyte Antigen- (HLA-)restricted epitopes. In this review, we discuss the advantages and limitations of these animal models and describe a novel "humanized" HLA transgenic rabbit, which shows spontaneous HSV-1 reactivation, recurrent ocular disease and mounts CD8(+) T cell responses to HLA-restricted epitopes. Adequate investments are needed to develop reliable preclinical animal models, such as HLA class I and class II double transgenic rabbits and guinea pigs to balance the ethical and financial concerns associated with the rising number of unsuccessful clinical trials for therapeutic vaccine formulations tested in unreliable mouse models.

Effect of sorafenib on experimental choroidal neovascularization in the rat

PURPOSE

This study was designed to evaluate the effect of sorafenib administration on laser-induced experimental choroidal neovascularization (CNV) in rats.

METHODS

A total of 36 rats were divided into three groups. Sorafenib, an oral, multitargeted receptor tyrosine kinase inhibitor, was administered at a dose of 10 mg/kg per day (n = 12) or 30 mg/kg per day (n = 12) for 1 day before the laser induction of CNV. Rats continued to receive the drug for 14 days. Fluorescein angiograms were analysed for CNV dye leakage and the thickness of CNV was assessed by histology. The levels of vascular endothelial growth factor, platelet-derived growth factor, monocyte chemoattractant protein-1 and intercellular adhesion molecule-1 mRNA were measured by the use of real-time quantitative reverse-transcription polymerase chain reaction.

RESULTS

Sorafenib-treated rats had significantly less fluorescence leakage as compared with vehicle-treated rats (P < 0.05), The CNV thickness in sorafenib-treated rats was significantly reduced as compared with vehicle-treated rats in a dose-dependent manner (P = 0.00163 for 10 mg/kg and P < 0.00001 for 30 mg/kg). After sorafenib (30 mg/kg) administration, expression of the vascular endothelial growth factor and intercellular adhesion molecule-1 genes was significantly decreased (P < 0.05 and P = 0.00802).

CONCLUSION

These results suggest that sorafenib may be potentially beneficial for the treatment of CNV in human; further studies on this subject are warranted.

Geldanamycin, a HSP90 inhibitor, attenuates the hypoxia-induced vascular endothelial growth factor expression in retinal pigment epithelium cells in vitro

Hypoxia is the most common factor contributing to the pathogenesis of choroidal neovascularization, which is the major cause for blindness and occurs in proliferative diabetic retinopathy and age-related macular degeneration. The purpose of this study is to investigate the role of retinal pigment epithelial (RPE) cells in the regulation of subretinal neovascularization under hypoxia and the possible function of a heat shock protein 90 (HSP90) inhibitor, geldanamycin (GA), in the regulation of VEGF expression. An in vitro hypoxic experimental model was used to mimic the ischemic microenvironment of RPE cells. The cell growth was measured by proliferation assay and the morphological observation was documented by microscope. The gene expression of VEGF, hsp70, hsp90alpha and hsp90beta were measured using semi-quantitative RT-PCR. The VEGF release from RPE cells were detected by ELISA. No alteration in growth rate and cell morphology under 1% O(2) condition for 24h was noticed. The proangiogenic growth factor VEGF, but not bFGF, released from hypoxia-treated cells were significantly higher than those of normoxic controls. A similar tendency of VEGF(165) isoform gene expression, detected by RT-PCR, was noticed in hypoxia-treated cells. Heat shock pretreatment elevated hsp70 and VEGF(165) gene expression and augmented the hypoxia-induced VEGF gene expression and protein release. Pretreatment with GA can significantly suppress the hypoxia-induced VEGF gene expression in and peptide release from RPE cells. These in vitro findings suggest that HSP90 inhibitors could be considered as novel anti-angiogenesis agents for diseases with intraocular neovascularization.

A novel vascular endothelial growth factor receptor 2 inhibitor, SU11248, suppresses choroidal neovascularization in vivo

AIM

An oral, multitargeted receptor tyrosine kinase inhibitor, SU11248, inhibits vascular endothelial growth factor receptor 2 (VEG FR2, kinase domain receptor F1K1), platelet-derived growth factor receptor, stem cell factor receptor (Kit), and fetal liver tyrosine kinase 3. In this study, we administered SU11248 beyond the completion of an experimental choroidal neovascularization (CNV) model to determine whether CNV growth can be inhibited in vivo.

METHODS

C57B6J mice were treated with daily oral administration (40, 80, and 150 mg/kg) of SU11248 during 5 days after diode laser endophotocoagulation and subjected to angiographic examination and histological analysis.

RESULTS

Intensity of fluorescein leakage from the experimental CNV decreased significantly compared to the control eyes. Histological study also revealed that the volume of CNV membrane was significantly reduced in the SU11248-treated eyes.

CONCLUSIONS

Oral administration of this compound is potentially beneficial in treating CNV caused by age-related macular degeneration (AMD) and other causal diseases. Considering the tolerance the clinical studies for malignant tumors previously demonstrated, further studies to evaluate the clinical efficacy of the drug for AMD might be indicated.

Localisation of SDF-1 and its receptor CXCR4 in retina and choroid of aged human eyes and in eyes with age related macular degeneration

AIM

To examine the immunolocalisation of stromal cell derived factor 1 (SDF-1) and its receptor CXCR4 in aged control human donor eyes and eyes with age related macular degeneration (AMD).

METHODS

Postmortem eyes from eight aged control donors (mean age 79.8 years) and from 12 donors with AMD (mean age 83.9 years) were cryopreserved and sectioned through the macular region. SDF-1 and CXCR4 were localised using streptavidin alkaline phosphatase immunohistochemistry and then sections were bleached. Three independent masked observers scored the immunohistochemical reaction product.

RESULTS

In aged control retinas, SDF-1 immunoreactivity was most intense in inner photoreceptor matrix (IPM). CXCR4 showed a similar pattern of immunostaining, but was more prominent in inner segments of photoreceptors. In aged control and AMD choroid, SDF-1 and CXCR4 localisations were most prominent in retinal pigment epithelial (RPE) cells and choroidal stroma. However, the intensity for SDF-1 was significantly reduced in RPE (p < 0.0001) and choroidal stroma (p < 0.05) in late AMD eyes. SDF-1 and CXCR4 immunoreactivities were weak or nearly absent in disciform scars with choroidal neovascularisation (CNV). Circulating cells, presumably leucocytes, were most intensely positive for CXCR4.

CONCLUSIONS

These results show that changes in distribution and relative levels of SDF-1/CXCR4 were not evident in early AMD. This suggests that SDF-1/CXCR4 may not contribute to the formation of CNV in AMD, in that CXCR4+ cells were not incorporated into neovascularisation. However, the examples of CNV studied were within disciform scars, so the authors cannot comment on the role of SDF-1/CXCR4 in the early stages of CNV formation.

A new animal model of choroidal neovascularization

PURPOSE

The purpose of this study was to evaluate the ability of different methods to induce choroidal neovascularization (CNV) in the domestic pig.

METHODS

A total of 26 Danish landrace pigs was used. A sample of 22 eyes in 12 pigs underwent retinal photocoagulation with a xenon lamp, six eyes in four pigs underwent retinal photocoagulation with a diode laser, and mechanical rupture of Bruch's membrane (BM) was induced in 12 pigs following surgical debridement of the retinal pigment epithelium without damage to the neuroretina.

RESULTS

All 12 pigs (100%) in the group with mechanical rupture of BM developed CNV. The induced membranes were morphologically similar to CNV membranes in humans. Induced CNV was found in 13 of 22 (54%) xenon lamp-treated animals and in five of six (83%) diode laser-treated animals. The CNV in these groups was small and the morphology of the induced lesions was dominated by retinal gliosis and retinal neovascularization, probably due to a marked destruction of the neuroretina.

CONCLUSIONS

Surgical debridement of the retinal pigment epithelium followed by mechanical rupture of BM is a reproducible method of producing CNV in the domestic pig, whereas photocoagulation gives rise to glially derived subretinal fibrovascular membranes and primarily retinal neovascularization.

Neointimal hyperplasia and vascular endothelial growth factor expression are increased in normoglycemic, insulin resistant, obese fatty rats

OBJECTIVE

Insulin resistance is associated with a constellation of factors that enhance the artherosclerotic process. Vessel injury results in the formation of a markedly increased neointima in type 2 diabetes. Increased neointimal hyperplasia (NH) and vascular endothelial growth factor (VEGF) expression may lead to restenosis post angioplasty. We studied NH and VEGF expression in an obese, insulin resistant, but normoglycemic rat model, after carotid balloon injury.

METHODS AND RESULTS

Diabetic rats (ZDF, n=10), normoglycemic, insulin-resistant rats (ZDF-normoglycemic, n=6) as well as Zucker fatty rats (FZ, n=6), and lean Zucker rats (LZ, n=6), all 13-16 weeks old, were subjected to right carotid injury by an angioplasty catheter introduced via the femoral artery. Three weeks later the rats were sacrificed and serum and carotids obtained. The intima-media ratio (I/M) was then calculated. ZDF-normoglycemic, FZ and ZDF-diabetic rats were all hyperinsulinemic and hypertriglyceridemic when compared to LZ rats. ZDF diabetic rats were hyperglycemic while FZ, ZDF-normoglycemic and LZ rats were normoglycemic. The I/M ratio for ZDF and FZ rats were significantly greater than for LZ rats. The VEGF expression was significantly greater in ZDF and FZ rats than LZ rats.

CONCLUSIONS

In conclusion, insulin resistance increases neointimal hyperplasia and VEGF expression even with normoglycemia, after carotid angioplasty in rats.

Identification of Chlamydia pneumoniae within human choroidal neovascular membranes secondary to age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness in the United States, and increasing evidence suggests that it is an inflammatory disease. The prokaryotic obligate intracellular pathogen Chlamydia pneumoniae is emerging as a novel risk factor in cardiovascular disease, and recent sero-epidemiological data suggest that C. pneumoniae infection is also associated with AMD. In this study, we examined choroidal neovascular membrane (CNV) tissue from patients with neovascular AMD for the presence of C. pneumoniae and determined whether the pathogen can dysregulate the function of key cell types in ways that can cause neovascular AMD. Nine CNV removed from patients with neovascular AMD were examined for the presence of C. pneumoniae by immunohistochemistry (IHC) and polymerase chain reaction (PCR); in addition, we performed PCR on nine non-AMD eyes, and IHC on five non-AMD CNV, seven non-AMD eyes, and one internal limiting membrane specimen. Finally, human monocyte-derived macrophages and retinal pigment epithelial (RPE) cells were exposed to C. pneumoniae and assayed in vitro for the production of pro-angiogenic immunomodulators (VEGF, IL-8, and MCP-1). C. pneumoniae was detected in four of nine AMD CNV by IHC and two of nine AMD CNV by PCR, induced VEGF production by human macrophages, and increased production of IL-8 and MCP-1 by RPE cells. In contrast, none of the 22 non-AMD specimens showed evidence for C. pneumoniae. These data indicate that a pathogen capable of inducing chronic inflammation and pro-angiogenic cytokines can be detected in some AMD CNV, and suggest that infection may contribute to the pathogenesis of AMD.

The relative contributions of each subset of ocular infiltrated cells in experimental choroidal neovascularisation

AIM

Choroidal neovascularisation (CNV) is a major cause of blindness in adults. The aim of this study was to investigate the role of infiltrating cells in the development of experimental CNV.

METHODS

CNV was induced in C57BL/6 (B6) mice by laser photocoagulation (PC). After PC, the numbers of each subset of infiltrated cells were analysed by flow cytometry at multiple time points. Each subset (except for macrophages) was depleted by the specific antibodies in vivo. Thereafter, the area of CNV was compared between the control B6 mice and the specific antibody treated mice 7 days after PC. The CNV formation in neutrophil depleted CC chemokine receptor-2 (CCR2) knockout mice was also examined to minimise the effects of macrophages.

RESULTS

In the early phase of CNV formation, a large number of neutrophils and macrophages infiltrated to the eyes. Natural killer (NK) cells and T lymphocytes were barely detected while no B lymphocytes were detected. The CNV areas did not significantly change compared between the control B6 mice and the specific antibody treated mice. However, the neutrophil depleted CCR2KO mice resulted in a reduction of CNV.

CONCLUSION

Although lymphocytes and NK cells had little effect on CNV formation, neutrophils partially contributed to CNV in the absence of macrophages.

Novel mechanism for age-related macular degeneration: an equilibrium shift between the angiogenesis factors VEGF and PEDF

We investigated gene expression profiles of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) in differentiated and non-differentiated retinal pigment epithelial (RPE) cells during oxidative stress. Human RPE cells were grown in culture on laminin-coated flasks to obtain differentiated features. Cells cultured on plastic were used as non-differentiated controls. After confluence, hydrogen peroxide (H2O2) was added for 48 h, then, total RNA was extracted and used for RT-PCR and Northern blot analysis. Medium conditioned by RPE was used for ELISA, Western blotting, and in vitro angiogenesis assay. As a result, differentiated RPE cells expressed significantly higher levels of VEGF protein, as compared to their non-differentiated counterparts. The expression pattern remained consistent even after cellular exposure to H2O2. Conversely, while elevated levels of PEDF transcript and protein were seen in differentiated RPE cells, compared to non-differentiated cells, a marked decrease at both PEDF mRNA and protein levels was seen after treatment with H2O2. Moreover, this decrease in PEDF expression was dosage dependent. In in vitro angiogenesis assay, conditioned medium from differentiated human RPE cells after exposure to H2O2 showed a dramatic increase in tubular formation and migratory activity of microvascular endothelial cells. These data suggest that, in physiological conditions, a critical balance between PEDF and VEGF exists, and PEDF may counteract the angiogenic potential of VEGF. Under oxidative stress, PEDF decreases disrupting this balance. This equilibrium shift may be significant in promoting a pathological condition of RPE cells and contributing to choroidal neovascularization in age-related macular degeneration.