Inhibition of NAD(P)H oxidase reduces apoptosis and avascular retina in an animal model of retinopathy of prematurity

Purpose: To study the mechanisms of action of the antioxidants, n-acetylcysteine (NAC), and the nicotinamide adenine dinucleotide phosphate (NAPDH) oxidase oxidase inhibitor, apocynin, on intravitreous neovascularization (IVNV), and retinal avascularity in a rat model of retinopathy of prematurity (ROP). Methods: Newborn rats exposed to oxygen-induced retinopathy underwent intraperitoneal (IP) injections of NAC (150 mg/kg) at post-natal day (p)2, p6, p10 (early NAC-treated), or p12 through p17 (late NAC-treated), apocynin (10 mg/kg) from p12 through p17, or phosphate buffered saline (PBS; controls). Lipid hydroperoxide (LHP) was measured in early NAC-treated oxygen-induced retinopathy (OIR) at p7, p14 and p18. Pups were placed in room air at p14. At p18, retinal flat mounts were scored for IVNV and avascular/total retinal area, or retinas were assayed for cleaved caspase-3 and vascular endothelial growth factor (VEGF) protein. In non-injected OIR pups, retinas were assayed for gp91phox. Cryosections were stained with isolectin B4, cleaved caspase-3, CD68, CD31, gp91phox, neuron-glial antigen 2 (NG-2), or anti-glial fibrillary acidic protein (GFAP) and visualized with confocal microscopy. Results: LHP increased over time in retinas from OIR exposed pups in association with IVNV. Early NAC-treated retinas had significantly reduced LHP compared to PBS-control at p18 (p<0.012). However, neither early nor late treatment with NAC had an effect on IVNV or retinal avascularity. Although apocynin had no effect on IVNV, it reduced both avascular retina (p=0.017) and retinal cleaved caspase-3 determined by western blot (p=0.021). In cryosections from OIR eyes, cleaved caspase-3 positive cells co-labeled with some lectin-stained vessels, NG2 labeled cells, and with GFAP positive cells in the inner nuclear layer. We found that the intravascular expression of gp91phox co-localized mostly with CD31 and some CD68 positive cells. Conclusions: Our results do not support the antioxidant properties of NAC as effective in reducing IVNV or avascular retina in the 50/10 OIR rat model. Apocynin reduced avascularity and apoptosis in the OIR model perhaps through pathways triggered by ROS generation but upstream from LHP production. Further study and consideration may be given to apocynin or NAD(P)H oxidase inhibitors as adjunctive therapy for ROP to reduce the avascular retina

VEGF isoforms and their expression after a single episode of hypoxia or repeated fluctuations between hyperoxia and hypoxia: Relevance to clinical ROP

Purpose—Fluctuations in oxygen are associated with the development of severe retinopathy of prematurity (ROP) in humans. However, the causal relationships between oxygen variability and severe ROP remain unknown. We investigated whether isoforms of vascular endothelial growth factor (VEGF) were differentially stimulated by hypoxia and by repeated fluctuations between hypoxia and hyperoxia, and whether isoforms were differentially expressed in association with intravitreous neovascularization. We also determined whether pigment epithelium-derived factor (PEDF) was dysregulated by oxygen fluctuations perhaps contributing to a delay in normal retinal vascular development. Methods—We used the 50/10 oxygen-induced retinopathy (50/10 OIR) model that exposes newborn rat pups to repeated cycles of 24 h of 50% oxygen alternating with 24 h of 10% oxygen to cause a condition similar to human ROP. Animals were euthanized at postnatal day 2 (P2; after one cycle of 50/10% oxygen), P7 (after 3.5 cycles of 50/10% oxygen), and P14 (after seven cycles of 50/10% oxygen). Room air raised control rat pups were also exposed to a single episode of 24 h of hypoxia at P7 and P14 and assayed immediately afterwards. Retinal VEGF isoforms and PEDF were measured by RT-PCR. Total VEGF protein was measured by ELISA. Results—We found that repeated cycles of hyperoxia and hypoxia caused greater expression of VEGF protein compared to control than did a single cycle of hyperoxia and hypoxia. VEGF164 mRNA had a greater fold change over control after repeated oxygen fluctuations than after a single episode of hypoxia. However, the other isoforms, VEGF188 and VEGF120, were expressed to a similar degree regardless of whether the stimulus was a single episode of hypoxia or repeated fluctuations in oxygen. VEGF164 was the predominant isoform expressed at the time of maximal intravitreous neovascularization. Retinal PEDF expression was elevated in pups in the 50/10 OIR model compared to control at P7, immediately after 50% oxygen. PEDF expression in the experimental group was similar to control at P18, when intravitreous neovascularization occurred. Conclusions—Repeated fluctuations in oxygen results in a greater expression of the pathologic isoform, VEGF164, than does hypoxia alone. However, the other isoforms were upregulated to an equivalent degree over control by repeated fluctuations in oxygen or a single episode of hypoxia. Total VEGF protein was increased to a greater degree by repeated fluctuations in oxygen compared to a single cycle of oxygen. PEDF was increased over control early in the 50/10 OIR model and may play a role in the observed delay in retinal vascularization. These findings provide insight into the effect of repeated oxygen fluctuations on the development of severe ROP in preterm infant

Exogenous leukemia inhibitory factor (LIF) attenuates retinal vascularization reducing cell proliferation not apoptosis

To study the effect of leukemia inhibitory factor (LIF) on rat retinal vascular development, Sprague–Dawley rats at postnatal age 3 days (p3) were given intraperitoneal (IP) LIF and analysis performed at p6 (p3/6). p7 rats were given intravitreous (IV) LIF and analysis performed at p9 (p7/9). Control animals were PBS injected. At the time of analysis retinal flatmounts were prepared and stained with Griffonia lectin and activated caspase-3. The retinal peripheral avascular area was measured and number of apoptotic cells counted. In vitro, human retinal microvascular endothelial cells (RMVECs) were cultured in media containing LIF, with and without neutralizing antibody to LIF. Cells were stained with activated caspase-3 and apoptotic cells counted. Proliferation was measured by counting cell numbers, and cell cycle stage was determined using propidium iodide staining and FACS analysis. LIF injected either IP or IV had no effect on body weight or total retina area, but significantly increased the peripheral retinal avascular area. In both IP and IV injected groups there was no difference in the number of apoptotic cells between PBS-or LIF-injected groups; although in the p7/9 retinas, both injected groups had significantly more apoptotic cells than the non-injected group. In vitro, there was no effect of LIF on RMVEC apoptosis; however, cell counts were significantly lower in the LIF-treated group. Antibody to LIF restored the cell counts to untreated levels. LIF reduced the number of cells in S phase. LIF attenuates retinal vascular development in vivo through growth arrest, and not apoptosis, of endothelial cells

Reduction in endothelial tip cell filopodia corresponds to reduced intravitreous but not intraretinal vascularization in a model of ROP

To determine the effect of a vascular endothelial growth factor receptor 2 tyrosine kinase (VEGFR2) inhibitor on intravitreous neovascularization (IVNV), endothelial tip cell filopodia, and intraretinal vascularization in a rat model of retinopathy of prematurity (ROP)

Heterotypic RPE-choroidal endothelial cell contact increases choroidal endothelial cell transmigration via PI 3-kinase and Rac1

Age-related macular degeneration (AMD) is the major cause of non-preventable blindness. Severe forms of AMD involve breaching of the retinal pigment epithelial (RPE) barrier by underlying choroidal endothelial cells (CECs), followed by migration into, and subsequent neovascularization of the neurosensory retina. However, little is known about the interactions between RPE and CECs and the signaling events leading to CEC transmigration. While soluble chemotactic factors secreted from RPE can contribute to inappropriate CEC transmigration, other unidentified stimuli may play an additional role. Using a coculture model that maintains the natural structural orientation of CECs to the basal aspect of RPE, we show that “contact” with RPE and/or RPE extracellular matrix increases CEC transmigration of the RPE barrier. From a biochemical standpoint, contact between CECs and RPE results in an increase in the activity of the GTPase Rac1 within the CECs; this increase is dependent on upstream activation of PI 3-K and Akt1. To confirm a link between these signaling molecules and increased CEC transmigration, we performed transmigration assays while inhibiting both PI 3-K and Rac1 activity, and observed that both decreased CEC transmigration. We hypothesize that contact between CECs and RPE stimulates a signaling pathway involving PI 3-K, Akt1, and Rac1 that facilitates CEC transmigration across the RPE barrier, an important step in the development of neovascular AMD

Neutralizing VEGF Decreases Tortuosity and Alters Endothelial Cell Division Orientation in Arterioles and Veins in a Rat Model of ROP: Relevance to Plus Disease

To study the effects of vascular endothelial growth factor (VEGF) on endothelial nitric oxide synthetase (eNOS) and retinal vascular tortuosity and cleavage planes in a rat model of retinopathy of prematurity (ROP)

Aqueous Vascular Endothelial Growth Factor as a Predictor of Macular Thickening Following Cataract Surgery in Patients With Diabetes Mellitus

To study associations between serum and aqueous vascular endothelial growth factor (VEGF) and insulin-like growth factor 1 (IGF-1) and macular edema measured with optical coherence tomography (OCT) following phacoemulsification in diabetic patients

Triamcinolone Reduces Neovascularization, Capillary Density and IGF-1 Receptor Phosphorylation in a Model of Oxygen-Induced Retinopathy

To study the effects of intravitreous triamcinolone acetonide (TA) on neovascularization (NV), capillary density, and retinal endothelial cell (REC) viability in a model of oxygen-induced retinopathy (OIR)

CCR3 is a target for age-related macular degeneration diagnosis and therapy

Age-related macular degeneration (AMD), a leading cause of blindness worldwide, is as prevalent as cancer in industrialized nations. Most blindness in AMD results from invasion of the retina by choroidal neovascularisation (CNV). Here we show that the eosinophil/mast cell chemokine receptor CCR3 is specifically expressed in choroidal neovascular endothelial cells in humans with AMD, and that despite the expression of its ligands eotaxin-1, -2 and -3, neither eosinophils nor mast cells are present in human CNV. Genetic or pharmacological targeting of CCR3 or eotaxins inhibited injury-induced CNV in mice. CNV suppression by CCR3 blockade was due to direct inhibition of endothelial cell proliferation, and was uncoupled from inflammation because it occurred in mice lacking eosinophils or mast cells, and was independent of macrophage and neutrophil recruitment. CCR3 blockade was more effective at reducing CNV than vascular endothelial growth factor A (VEGF-A) neutralization, which is in clinical use at present, and, unlike VEGF-A blockade, is not toxic to the mouse retina. In vivo imaging with CCR3-targeting quantum dots located spontaneous CNV invisible to standard fluorescein angiography in mice before retinal invasion. CCR3 targeting might reduce vision loss due to AMD through early detection and therapeutic angioinhibition

The Role of RPE Cell-Associated VEGF189 in Choroidal Endothelial Cell Transmigration across the RPE

Contact between RPE and choroidal endothelial cells (CECs) is an important step preceding vision-threatening neovascular AMD, a leading cause of legal blindness worldwide. However, no animal model or clinical study has focused on the effects of this contact. The physiologically relevant in vitro coculture model allows study of the effects of RPE and CEC interactions and contact on signaling pathways within each cell type and on CEC transmigration across the RPE. The authors show that VEGF189, a splice variant of VEGF, is upregulated by stressors found in AMD and by contact with CECs. This upregulation triggers activation of Rac1 mediated through VEGFR2 to increase CEC migration across the RPE